Mingledorff's Support Site

Documentation & Installation: Is It Important?

Wed, 08 Jul 2026 14:59:44 GMT

Disclaimer: The technical statements, information and recommendations contained herein are believed to be accurate as of the date hereof, but Mingledorff’s does not make representations or warranties, express or implied, as to its accuracy, its completeness, or the results to be obtained. The information is being provided for informational purposes only and is intended for use by persons having adequate skill and expertise regarding the proper selection, use and application of the products and recommendations and at their own risk and discretion.

Coming back to work after an extended weekend of 4th of July there’s paperwork handed to you for the emergency installation of a system in an elderly person’s home. It’s to replace the existing system with a more efficient slim duct indoor unit paired with a ductless mini-split condenser.

You try to be as clean as possible not to leave dirty boot prints, the carpet is already stained and dirty, but you don’t want to contribute to the problem. This keeps the customer for next time, if not for life, and they notice this.

To stick with keeping things clean, you clean up the workspace while you let the system run for testing. Garbage is all cleaned up including the paperwork and any unneeded accessories for the installation. No one reads the paperwork anyway with the use of apps on phones these days, right? Right? WRONG!

Fast forward 6 months. The customer calls that their home isn’t heating and your company stands by their work. They send out a service technician to investigate free of charge. The system is new, nothing “SHOULD” be wrong.

The service technician’s phone is dead after running service calls all day. This leaves the technician without a fallback for error codes indications, troubleshooting trees, and wiring diagrams for the system. The technician calls their local Mingledorff’s Technical Support team for help. They must walk through the entire system using the exact manuals “someone” threw away.

After some time, it’s determined that the thermostat, wiring, or Indoor unit’s board is the root cause. Technical Support asks if they have the original wireless remote and a “candy bar” IR receiver on site. Without the remote or the IR receiver there isn’t a way to fully diagnose the system or manually get it into operation to test it. This becomes a guessing game of throwing parts at a new system to see what works. A snowball effect stemming from day 1 at install.

Leaving the documentation and accessories on the jobsite in the original bag can lead to less time spent diagnosing a system and could also be the tipping point of whether a system can manually limp along.

How this should have gone:

With the proper tools left from the install on site, the technician was able to wire in the IR Receiver to see there was a communication error code between the indoor unit and the thermostat. They were then able to unwire the wall thermostat and test it using the wireless remote and the IR module. The cause was then limited down to the wire or wall thermostat. Technician was able to ohm out the wire and found a picture frame was hung recently over the thermostat and had damaged the wire within the wall. Until new wire could be run the thermostat was left unwired and the system set to run automatically using the manual button on the IR module. The system will maintain its set point without a wired remote attached using the return air sensor built into the unit.

The process took less than 30 mins to check and get back running rather than the hours the prior scenario took to come to the exact same outcome. Customers were just happy to have their heat back on, even if they couldn’t control it for now. This leads to better customer relationships and efficiency of time spent on service calls.

Please leave manuals and accessory items with the install rather than throwing them away. Your service technician and Mingledorff’s Technical Support team will thank you greatly.

Equipment Verification Technician • Southeast Region

Anthony Coker

June 10, 2026

Documentation & Installation: Is It Important?

Taking NATE Online

Wed, 08 Jul 2026 14:39:44 GMT

We have recently begun teaching our NATE classes online using zoom format. This article will hopefully clear up some of any tech’s fears about online review and testing.

To begin with our NATE classes are advertised in our newsletter and on heatcool.com.

Pick the class you would like to take, whether it is core or heat pumps. Upon registration, you will be sent an acceptance acknowledgement along with core and heat pump study guides.

In a few days, the instructor will send you a welcome letter along with the study guides once again. Please be aware if your company signs you up with the company email, and not your personal email, all correspondence will be sent to that email. Please be aware if you are taking the class so you can receive all correspondence for the class along with all study materials.

The NATE class and exam will be taught via the zoom format. Please get familiar with the zoom format either with your manager or searching at your convenience to simplify the class-on-class day. It is a relatively easy program to navigate once you get the zoom program downloaded.

The instructor will send you a zoom invitation one to two days before the class and exam date. Be looking at your emails and aware of the zoom invitation email.

Please respond back to the instructor you have received the correspondence and can navigate via zoom.

The instructor will log in at 7:30 am on the day of the exam, to take care of glitches, etc. You may log in any time after 7:30 also. The class will begin at 8:00 am. We will break for lunch around 11:00 am and have a couple of breaks during the day. The exam should begin right after lunch. You should be completed in 1 to 2 hours. Remember all times are based on Eastern Standard Time. If you are in Cent ral Standard Time, please log in 1 hour earlier.

The exams are timed. The core exam is given 1 and a half hours. The heat pump exam is 2 and one half hours.

On the day of testing after the review period is over, you will receive an email from noreply-assessments@meazurelearning.com . This email will contain your individualized password to access your test. Please add this email to your contacts so that it is not lost to spam or company firewalls. You will need to minimize zoom and log in to this website to take the exam. The exam will be recorded by the instructor to minimize someone attempting to help the tech taking the exam. The instructor will ask for the student’s ID before test time. Tech will need to fill out mandatory name, address, and other vital information before beginning the exam.

You will have access to dropdowns of formulas on each exam. You can move forwards or backwards to check and recheck your answers.

Once you have completed, you will need to check “I am completed” and this will grade your exam. You will know immediately your score, whether you pass or fail.

The key is to review the study guides several times before the exam. This, along with your tech experience, should be enough to be successful in passing the NATE exams.

Please contact me at klivingston@mingledorffs.com , or call or text me at 470-214-4374 if you have any questions about the review and exam.

We hope this article may clear up any questions about NATE online classes and testing.

Once again, thank you for choosing Mingledorff’s for your training.

Frequently Asked Questions:

Q: Where do I take online classes?

A: You may take the class and exam at the office, or at your residence. You need to be sure and have good internet connections. Your location needs to be quiet so the tech can concentrate.

Q: Can I use an IPAD or phone to take the class and exam?

A: NATE can’t support and IPAD or phone should there be a glitch or loss of signal. NATE recommends using a laptop or computer with camera.

Q: Can I take other NATE exams online as well?

A: We will be offering other NATE online topics in the future.

Q: How much is the class and exam?

A: Currently $200.00. This is subject to change.

Q: Can we share the laptop or computer with other techs?

A: No the class is limited to one tech per computer

Q: How do I receive the certification once I pass the exams?

A: You will receive an email from NATE with your number and a way to print out your certificate.

Technical Services Manager North Georgia District

Anthony Coker

June 10, 2026

Taking NATE Online

Crossover and Zoning

Mon, 29 Jun 2026 14:24:15 GMT

Carrier has approved the use of Crossover equipment with zoning applications. The instructions for this will be released in several phases during 2026. Release dates for the different phases of instructions are subject to change.

First phase:

Instructs using a residential (non-Crossover) fan coil with a 37MURA or 37MUHA outdoor unit and ZONECC4ZCN01 zone controller. (May 6, 2026)

Second phase:

Instructs using a 45MUAA or 45MUHA matched with a 37MURA or 37MUHA, communicating on S1/S2. (May 21, 2026)

Third phase:

Instructs using a residential furnace and coil with a 37MURA or 37MUHA outdoor unit in a dual fuel application. (May 30, 2026)

*See product bulletin 101-26-13 (Carrier) or BY-103-26-13 (Bryant) for complete instructions.

Important things to consider for zoning when using Crossover equipment:

1. Static pressure. The blowers provide a constant air volume based on the mode of operation. The 45MUAA fan coils can handle up to .8” static, above which CFM performance falls off dramatically. The 45MUHA 18-36K are rated up to 1” static. 45MUHA 48-60K are rated at .8”. 

2. Bypass. Because of the constant air volume motor, the blower is likely to hunt if static pressure changes significantly while running. It is also necessary to use the dump zone method vs bypassing supply air directly into the return. When using the standard supply-to-return bypass method, the T1 (return air) thermistor will be deceived any time the bypass damper opens due to direct supply air on the sensor. See below for an example of a dump zone design.

Technical Services Manager North Georgia District

Anthony Coker

June 10, 2026

Taking NATE Online

3. The Algorithm. Capacity request (CR) and target evaporator setpoint (TES) are at the core of logic driving the inverter frequency. This is a very important difference from a standard or Infinity/Evolution zone system. CR is calculated from indoor temperature vs setpoint. TES is based on mode of operation (heat or cool) and Y1 vs Y2 demand. But how does the logic determine what these temps are?

When the outdoor unit is matched to a non-communicating fan coil, the CR and TES are derived from a refrigerant pressure transducer (reading suction in cooling or discharge in heating) combined with a thermistor (reading dedicated suction temperature). From these components, it determines TES and CR, building a memory of the sensor readings when the system thermals on and off (setpoint).

When the outdoor unit communicates with the indoor unit, CR is derived from the T1 thermistor and learned setpoints from building a memory of the T1 temperature when the system thermals on and off. TES is monitored from the T2 (Indoor coil).

The 45MUAA and 45MUHA fan coils also have logic for TES based on T2A and T2B thermistors (indoor coil refrigerant entering and leaving temperatures) which direct the EEV to open or close as needed during the cooling cycle.

Other factors in the algorithm for inverter frequency are outdoor ambient, outdoor coil, compressor discharge, and IPM temperatures.

Be aware Carrier has not validated any third-party zoning for use with the Crossover equipment. The instructions will be revised and re-issued at times. Always refer to the most up-to-date literature which can be found on HVACPartners.

Addendum (6/23/26):

Carrier’s compliance with CVP (Control Verification Procedure) requires that the Crossover outdoor units be wired for communication only. It will be necessary to add a 24-volt interface (KSAIC0701230) with any non-communicating indoor unit, and that when a Crossover fan coil is used, it must be wired for communication.
*The built-in interface on the Crossover outdoor unit will remain for emergency use only.

References:

Product Bulletin: 101-26-13
Product Bulletin: BY-103-26-13
CA-Crossover-Zoning
BR-Crossover-Zoning
37MURA-02SI.pdf
37MUHA-02SI.pdf
45MUAA-02SI.fm
45MUHA-03SI.fm
ZONE4CN-02SISP.pdf

How HVAC Technicians Can Stay Hydrated During the Summer

Wed, 10 Jun 2026 15:19:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

How HVAC Technicians Can Stay Hydrated During the Summer

HVAC technicians often work in attics, rooftops, mechanical rooms, and outdoor environments where temperatures can become dangerously high. Proper hydration helps maintain energy, concentration, and safety throughout the workday.

1. Start Hydrating Before Work

Begin drinking water before your shift starts. Waiting until you feel thirsty means you may already be mildly dehydrated.

2. Drink Water Regularly

Take small, frequent drinks throughout the day rather than consuming large amounts at once. A good goal is to drink water every 15–20 minutes when working in hot conditions.

3. Replace Lost Electrolytes

Heavy sweating causes the loss of electrolytes such as sodium and potassium. During long periods of heat exposure, consider electrolyte drinks or electrolyte tablets in addition to water.

4. Monitor Urine Color

A simple way to check hydration is urine color:

Pale yellow = well hydrated
Dark yellow or amber = drink more fluids

5. Avoid Excessive Caffeine and Energy Drinks

Large amounts of coffee, energy drinks, and sugary beverages can contribute to dehydration and may increase heart rate during strenuous work in hot environments.

6. Eat Hydrating Foods

Include foods with high water content, such as:

Watermelon
Oranges
Grapes
Cucumbers
Lettuce

7. Use Insulated Water Bottles

Keep water cool by carrying an insulated bottle or cooler. Cold water is often more appealing and encourages frequent drinking.

8. Take Cooling Breaks

Whenever possible, rest in shaded or air-conditioned areas. Cooling down reduces sweat loss and helps your body recover.

9. Know the Signs of Heat Stress

Watch for:

Excessive thirst
Dizziness
Headache
Fatigue
Muscle cramps
Nausea
Confusion

If these symptoms occur, stop work, move to a cool location, and rehydrate immediately.

10. Follow a Hydration Plan

For technicians working in extreme heat:

Drink water before work.
Continue drinking regularly throughout the day.
Use electrolyte replacement during heavy sweating.
Rehydrate after work to replace fluids lost during the shift.

Proper hydration is not only a comfort issue it’s a critical safety practice that helps HVAC technicians maintain productivity, reduce fatigue, and prevent heat-related illnesses during the summer months.

June 10, 2026

No “Os” in Commercial Heat Pumps

Wed, 10 Jun 2026 14:35:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

No “Os” in Commercial Heat Pumps

Have you ever installed or started up a commercial heat pump? Did you notice there is not an “O” terminal on the units?

Commercial heat pumps do not operate like the residential heat pumps in regard to controls. I have taken several calls in the last few weeks where the heat pump was not working correctly and doing strange stuff. I always ask the tech how the thermostat is configured and I always get the same answer “Iits setup for heat pump.” This is the wrong way to do this. There is no “O” terminal anywhere on the units because we do not use an”O” terminal, we are not energizing the reversing valve with “O.”

All the logic is done through the defrost board. When you energize 24v to Y1 it knows to run in cooling, and when you energize 24v to W1 it knows to run in heat pump heating.

When you install and set up the thermostat you configure it for conventional heat, basically telling it that it is a straight cool unit with heat using Y1, Y2 for cooling and W1 for heating. Do this and you wont have any problems.

I do recommend the Pro1 T855 for the commercial heat pumps so you can set up the minimum run time for 5 minutes to prevent a nuisance fault code 3 on the CADM. Please see my article on fault code 3 HERE.

All of this info is found in the install manuals that come with the unit. Below are some helpful reference images.

June 10, 2026

Simplified Wiring Guide for R, Y1, Y2 Terminals

Wed, 10 Jun 2026 11:48:43 GMT

Anthony Coker

Technical Services Manager North Georgia District

Simplified Wiring Guide for R, Y1, Y2 Terminals

Y1 Terminal

UCB THERMOSTAT Y1 TERMINAL

UCB ECON Pin1 Blue to

PL6 Pin2 Blue Loop Plug

PL6-R Pin2 Blue Loop Plug

PL6-R Pin5 Blue Loop Plug

PL6 Pin5 Gray Loop Plug

UCB ECON Pin2 Gray

UCB REHEAT/HP Pin1 Gray

REHEAT CONTROL Pin6 Gray

REHEAT CONTROL Pin5 Gray*

UCB REHEAT/HP Pin2 Gray*

UCB COMP Pin2 and

UCB to LPS1 to

UCB HPS1 to

UCB Comp Pin3 to

FTP to

COFS to

CC Compressor Contactor

Y1 Terminal (You now have Y1)

The next series will show W1, W2 and Reheat! In various configurations, like UCB, CTB etc…

The link to wiring diagram above shows color paths for colors above and two diagrams one for Siemens economizer and Honeywell (Jade) W7220 control on the other diagram.

R Terminal

24VAC TRANSFORMER1

UCB Main Pin1

UCB Unit Shutdown Smoke Shutdown A 24VAC OUT

UCB Unit Shutdown Smoke Shutdown B

UCB Unit Shutdown Remote Shutdown A

UCB Unit Shutdown Remote Shutdown B

UCB PMR 24V A

UCB PMR Cont B

UCB Main Pin7

LSM

UCB Main Pin8

R Terminal (You Now have R)

Y2 Terminal

UCB THERMOSTAT Y2 TERMINAL

UCB ECON Pin4 Yellow to

PL6 Pin8 Yellow Loop Plug

PL6-r Pin8 Yellow Loop Plug

PL6-R PIn9 Yellow Loop Plug

PL6 Pin9 Orange Loop Plug

UCB ECON Pin3

UCB REHEAT/HP Pin3 Orange

REHEAT CONTROL Pin11 Orange

REHEAT CONTROL Pin10 Orange*

UCB REHEAT/HP Pin4 Orange*

UCB COMP Pin1

LDR (LOADER)

Y2 Terminal(You now have Y2)

Tip: click the images to open an enlarged view in another tab. Close the tab to return to the article.

June 10, 2026

Schematic examples of the Safety Chain for RTU’s – Part 3

Mon, 18 May 2026 16:58:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Schematic examples of the Safety Chain for RTU’s – Part 3

On the first Tech-Tip we went over the R looper wire which went through Pins 7 and 8 on UCB Main like below as well as the LSM.

In the second Tech Tip of this series, we went over examples of the UCB going to a (VFD) Variable Frequency Drive.

In this one, we will discuss Commercial Air Handlers / 40RL R454B 07-12 Dissipation and EcoBlue.

June 10, 2026

Example 1: Commercial Air Handler / 40RL R454B 07-12 Dissipation and EcoBlue

Details for Example 1:

IDBC 24vac from transformer goes to UCB Main Pin 1

Smoke Shutdown A

Smoke Shutdown B

Remote Shutdown A

Remote Shutdown B

Phase Monitor (PMR) A(24v)

Phase Monitor (PMR) B(CONT)

Main Pin 7

PL12 Pin 1

PL1 Pin 8

PL1 Pin 11

PL12 Pin 2

RDB J1 Pin 5 Through R4 to

RDB J1 Pin 4

Main Pin 8

Now to look at a CTB board same concept but different pins.

Note: the dark lines represent boards and controls. Notice the dark line around the IGC board as well as the dark lines around the CTB or Control Terminal Board.

You now have R!

On the picture above:

R Safety Circuit for CTB. CTB uses (Pin10 – Pin11)

Transformer

CTB Contl Board Pin9

CTB Smoke Shutdown A

CTB Smoke Shutdown B

CTB Remote Shutdown A

CTB Remote Shutdown B

CTB Phase Monitor A (24v)

CTB Phase Monitor B (Cont)

CTB Contl Board Pin11

CTB IFM OL A

CTB IFM OL B

CTB Contl Board Pin10

CTB R

COMMERCIAL DEFROST BOARD

24vac from Transformer to ground

Note: Jumper should be on R and W1

CTB W1

CTB Reheat/HP Pin4

Defrost Board P2 Pin7

P3 Pin10

FPT Entering

FPT Leaving

CTB Reheat/HP Pin6

CTB CLO1/COMP1 Pin4

CTB CLO1/COMP1 Pin5

CTB LPS1 Entering

CTB LPS1 Leaving

CTB HPS2 Entering

CTB HPS2 Leaving

CTB CLO1/COMP1 Pin6

Contactor 24vac side.

Now you have voltage on R!

You now have W1!

COMMERCIAL IGC BOARD (Y1 CIRCUIT WALKTHROUGH)

CTB Y1

Note: Jumper should be on R and Y1

CTB Y1

CTB Econ Pin1

CTB PL6 Pin2

CTB Pl6R Pin2

CTB Pl6R Pin5

CTB Pl6 Pin 5

CTB Econ Pin2

CTB Reheat Pin6

CTB CLO1/COMP1 Pin4

CTB CLO1/COMP1 Pin5

CTB LPS1 Entering

CTB LPS! Leaving

CTB LPS2 Entering

CTB LPS2 Leaving

CTB CLO1/COMP1 Pin6

Contactor 24vac side.

Wiring Diagram for Commercial Defrost Board

You now have Y1!

Diagram for: COMMERCIAL IGC BOARD (Y1 CIRCUIT WALKTHROUGH)

You now have R!

Example 2: Commercial Air Handler / 40RL R454B Dissipation With VFD

Details for Example 1:

IDBC 24vac from transformer

UCB Main Pin 1

UCB Smoke Shutdown A

UCB Smoke Shutdown B

UCB Remote Shutdown A

UCB Remote Shutdown B

UCB Phase Monitor (PMR) A(24v)

UCB Phase Monitor (PMR) B(CONT)

UCB Main Pin 7

PL12 Pin 1

PL1 Pin 8

VFD Drive ACH180 use 6/ACH580 use 25. RO1 Relay Output 1 Source (NO Power off)( NC Power on)

VFD Drive ACH180 use 7/ACH580 use 27. RO1 Relay Output 1 Source

PL1 Pin 11

PL12 Pin 2

RDB J1 Pin 5 Through R4 to

RDB J1 Pin 4

UCB Main Pin 8

Tip: click the images to open an enlarged view in another tab. Close the tab to return to the article.

Updates for Carrier/Bryant Smart Thermostats

Mon, 18 May 2026 16:02:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Updates for Carrier/Bryant Smart Thermostats

Are you selling, installing, serving or using the new Carrier or Bryant smart thermostat?

Carrier and Bryant have pushed a software update and you will need to do a factory reset on the thermostats. The update should have taken place with no interruptions to the system and how it operates.

When you go out to see your existing customer with the smart thermostat go ahead and make it part of your maintenance routine and perform a factory reset. Use the Carrier/Bryant service tech to reprogram the smart thermostat and recheck all the lockout factory defaults.

I personally use the smart thermostat and I did not notice any problems when it updated, I did perform the (FR) factory rest and reconfigured the thermostat. All relevant update info can be found on HVACPartners. Follow the reset instructions provided for a seamless update. You can see detailed scenarios below that offer update guidance.

June 10, 2026

This article is only in reference to models: TSTATCCEWF-01 & TSTATBBEWF-01.

Benefits of Using Megohmmeters for Troubleshooting

Mon, 18 May 2026 14:47:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Benefits of Using Megohmmeters for Troubleshooting

A megohmmeter (often called a “Megger,” after the well-known brand Megger) is a specialized instrument used to measure very high electrical resistance, especially insulation resistance in cables, motors, transformers, and electrical systems.

Benefits of Using Megohmmeters for Troubleshooting

1. Detects Insulation Breakdown Early

Megohmmeters can identify weakening insulation before it completely fails. This helps prevent:

Electrical shorts
Ground faults
Equipment damage
Unexpected downtime

For example, moisture, dirt, heat, or aging insulation may slowly reduce resistance over time. A megohmmeter reveals these issues early.

2. Improves Safety

Poor insulation can expose workers to:

Electric shock
Arc flash hazards
Fire risks

By verifying insulation integrity, technicians can ensure circuits and equipment are safe before energizing them.

3. Helps Locate Hidden Faults

Standard multimeters may not detect high-resistance leakage paths. Megohmmeters apply a higher DC test voltage, making it easier to find:

Damaged cable insulation
Moisture intrusion
Contamination
Cracked motor windings

This is especially useful in industrial troubleshooting.

4. Reduces Equipment Downtime

Routine insulation testing allows maintenance teams to identify problems before catastrophic failure occurs. Predictive maintenance reduces:

Emergency repairs
Production interruptions
Replacement costs

5. Verifies Repairs and Installations

After repairing or installing electrical equipment, megohmmeters confirm insulation quality before the system is placed into service.

Common applications include:

Motors
Generators
Switchgear
Transformers
Power cables

6. Supports Preventive Maintenance Programs

Trending insulation resistance readings over time helps technicians monitor equipment condition.

If resistance values gradually decrease, maintenance can be scheduled before failure happens.

7. More Accurate for High Resistance Measurements

A standard ohmmeter is not designed for measuring insulation in the megohm or gigohm range. Megohmmeters provide:

Higher test voltages
Greater measurement range
Better accuracy for insulation testing

Typical Troubleshooting Uses

Technicians commonly use megohmmeters to troubleshoot:

Motor winding insulation failures
Underground cable faults
Moisture in electrical panels
Transformer insulation degradation
Industrial machine leakage currents

Important Safety Note :

Megohmmeters generate high DC voltages (commonly 250 V, 500 V, 1000 V, or higher). Equipment should be:

De-energized
Properly isolated
Discharged after testing

Always follow electrical safety procedures and manufacturer recommendations.

The Negative Side of Using a Megohmmeter

A megohmmeter, often called a “megger,” is a valuable tool used to test insulation resistance in motors, cables, transformers, and electrical equipment. While it helps identify insulation problems and prevent electrical failures, improper use of a megohmmeter can create several disadvantages and risks.

1. Can Damage Sensitive Equipment

Megohmmeters apply high DC voltage during testing, commonly ranging from 250V to 5,000V or higher. This voltage can damage:

Electronic circuits
Variable frequency drives (VFDs)
PLCs and control boards
Sensors and communication devices

If sensitive components are not disconnected before testing, the equipment may fail or become unreliable.

2. Safety Hazards to Technicians

Using a megohmmeter incorrectly can expose workers to electric shock. Because the instrument generates high voltage, there is a risk of:

Electrical burns
Arc flash incidents
Shock from charged cables or motors

Proper lockout/tagout procedures and personal protective equipment (PPE) are necessary before testing.

3. Incorrect Readings from Improper Testing

Megger readings can be misleading if the test is performed incorrectly. Factors that affect readings include:

Moisture
Temperature
Dirty insulation
Improper grounding
Testing equipment while still connected in the circuit

False readings may lead to unnecessary repairs or overlooked failures.

4. Requires Equipment Shutdown

Most insulation resistance testing must be performed with the equipment de-energized. This means:

Production downtime
Maintenance interruptions
Delays in operations

In industrial facilities, shutting down major systems can be costly and time-consuming.

5. Can Weaken Old Insulation

Applying high test voltage to aged or deteriorated insulation may further weaken it. In some cases, the insulation may fail during the test itself. Older motors and cables are especially vulnerable.

6. Limited Diagnostic Information

A megohmmeter only measures insulation resistance. It does not identify:

Exact fault locations
Mechanical problems
Loose electrical connections
Load-related issues

Additional testing methods are often required for a complete diagnosis.

7. Requires Skilled Interpretation

Reading megohmmeter results is not always simple. Technicians must understand:

Acceptable resistance values
Polarization index (PI)
Dielectric absorption ratio (DAR)
Equipment manufacturer standards

Without proper training, test results may be misunderstood.

Conclusion

Megohmmeters are important tools for preventive maintenance and insulation testing, but they also have disadvantages. High test voltage can damage sensitive equipment, create safety hazards, and produce misleading results if used improperly. Proper procedures, training, and equipment isolation are essential to ensure safe and accurate megger testing.

June 10, 2026

The Importance of Maintaining Vacuum Pumps With Oil Changes

Wed, 15 Apr 2026 14:53:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

The Importance of Maintaining Vacuum Pumps With Oil Changes

Maintaining vacuum pump oil and changing it regularly is very important—especially in HVAC work. Here’s why it matters and what happens if you don’t.

Why vacuum pump oil changes are important:

1. Removes moisture from systems

The main job of a vacuum pump is to pull moisture and air out of a refrigeration system.
Dirty oil becomes saturated with water and can’t remove moisture effectively.

2. Maintains deep vacuum performance

Clean oil helps the pump reach lower microns faster.
Contaminated oil prevents pulling a proper vacuum, leading to system problems later.

3. Protects internal components

Oil lubricates seals, vanes, and bearings.
Dirty oil causes excess wear, overheating, and shorter pump life.

4. Prevents contamination

Old oil contains acids, debris, and refrigerant residue.
These contaminants circulate inside the pump and reduce efficiency.

5. Speeds up evacuation time

Fresh oil allows the pump to work faster, saving time on installations and repairs.

What happens if you don’t change the oil?

Cannot pull below 500 microns
Moisture stays in the system
Compressor failure risk increases
Pump overheats
Pump life shortens
Multiple oil changes required later anyway

Best practices:

Change oil after every major evacuation
Change oil when it looks cloudy or milky
Warm up pump before draining for better removal
Use manufacturer-recommended vacuum pump oil
Keep extra oil in your truck

Quick Visual Check Guide:

June 10, 2026

Clear oil = Good

• Dark / burnt = Contamination

• Cloudy / Milky = Moisture present

Regular oil changes help you pull deeper vacuums, protect compressors, and extend pump life — all critical for quality HVAC work.

Spring Cleaning: The Importance of Spring Maintenance

Mon, 13 Apr 2026 16:17:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Spring Cleaning: The Importance of Spring Maintenance

It is very important this time of year for spring maintenance for the air conditioning system.Proper annual maintenance will help the life of the system and efficiency of the system as well as find potential problems helping prevent breakdowns.

You can use the check list below for your Spring Maintenance routine.

Let’s start with the indoor unit. Change filters, clean out drain lines, and check all electrical connections by taking volt readings and amp readings on the blower motor. Then, inspect the evaporator coil and make sure it is clean.

Moving to the outdoor unit, it is very important to check and verify proper operation and cleanliness of the coil. Check the line voltage going to the unit as well as all electrical connections. Check the contactor and capacitor and be sure to check amp draw of the compressor and outdoor fan motor.

Lastly, always check the charge of the system. Check the pressure on both liquid and suction and the superheat and subcool of the system. If you want to clean the unit, start by cleaning any dirt and leaves from the inside of the unit. Clean the conditioner coil with a good, recommended coil cleaner and water solution and rinse with fresh water.

June 10, 2026

Schematic examples of the Safety Chain for RTU’s – Part 2

Thu, 09 Apr 2026 19:59:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Schematic examples of the Safety Chain for RTU’s – Part 2

On the picture above you have VFD Drive Terminals.

RO1 Relay Output 1 Source which is either

(NO) = Normally Open which is Power off or

(NC) = Normally Closed which is Power on.

All of this is inside the VFD drive. Now we will leave the VFD drive and head back to the UCB Main Plug to complete our circuit.

Now check voltages from these pins to ground.

VFD Drive ACH180: use 7 which is the RO1 Relay Output 1 Source in the VFD Drive.
PL1 Pin 11
PL12 Pin2
UCB Main Pin8

Now you have voltage on R!

On the first Tech-Tip we went over the R looper wire which went through Pins 7 and 8 on UCB Main like below as well as the LSM.

In this Tech Tip, we will go over Pins 7 and 8 again with the red looper wire as well as go over the one with the UCB going to a (VFD) Variable Frequency Drive.

Note: The yellow letters are between Pin 7 and 8 on UCB Main!

Note: Check all voltages to ground.

Example: 24VAC Transformer Secondary to ground. Then UCB Main at Pin1 to ground then

Smoke Shutdown A to ground etc, etc…

If you have voltages all the way to Pin8 on UCB Main then you will have Voltage on R terminal.

Tip: click the images to open an enlarged view in another tab. Close the tab to return to the article.

June 10, 2026

Example 1: 48FC 04-07 RED LOOPER WIRE

Details for Example 1:

24vac from transformer
UCB Main Pin 1
UCB Smoke Shutdown A
UCB Smoke Shutdown B
UCB Remote Shutdown A
UCB Remote Shutdown B
UCB Phase Monitor (PMR) A(24v)
UCB PMR B(CONT)
Main Pin 7
Just a RED wire in a loop from UCB Main Pin 7 to Pin 8
UCB Main Pin 8

You now have R!

24vac from transformer
UCB Main Pin 1
Smoke Shutdown A
Smoke Shutdown B
Remote Shutdown A
Remote Shutdown B
Phase Monitor (PMR) A(24v)
PMR B(CONT)

Example 2: Commercial Air Handler/ 40RU 410A with VFD

NOTE: Everything with yellow letters is between Pin 7 and 8 on UCB Main in this example

UCB Main Pin 7
PL12 Pin1
PL1 Pin8

ACS320 Drive, which has orange boxes around it in the photo below.

The ACH180 is the yellow boxes which will use Terminal 6 that will be the drive that we use for this example.

The ACH550 and the ACH580 will be the blue boxes which will use Terminal 25. I just want to make sure you see how they have written the numbers.

Schematic examples of the Safety Chain for RTU’s – Part 1

Mon, 09 Mar 2026 20:32:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Schematic examples of the Safety Chain for RTU’s – Part 1

In this series of Tech-Tips articles, we will be going over some of the wiring diagrams and their paths for simplifying troubleshooting.

Examples in this series will be: R, G, Y1, Y2, W1, W2 through various boards as well as types of fans being used like Direct Drive, VFD or Ecoblue, as well the (RDB) Refrigerant Dissipation Board.

Each measurement will be taken from the testing point to ground after verifying you have voltage to common. Then, you move on to the next test point and verify each one until you find where you are losing your voltage.

The 1st example is a UCB board which has a looper wire on pins 7 and 8.

You now have “R!”

Remember to check all voltages to ground.

Example: 24VAC to ground at Pin 1 on UCB Main, then Smoke Shutdown A to ground etc, etc… If you have voltages all the way to Pin 8 on UCB Main then you will have Voltage on R terminal.

The 2nd example has a (LSM) Limit Switch Manual in it. Both are the R circuit. The next few Tech-Tips will have various wiring diagrams with different locations on Pins 7 and 8 as well as other paths we will cover individually.

Tip: click the images to open an enlarged view in another tab. Close the tab to return to the article.

June 10, 2026

Example 1: 48FC 04-07 RED LOOPER WIRE

Details for Example 1:

24vac from transformer
UCB Main Pin 1
Smoke Shutdown A
Smoke Shutdown B
Remote Shutdown A
Remote Shutdown B
Phase Monitor (PMR)
A(24v)
PMR B(CONT)
Main Pin 7
Just a RED wire in a loop from Pin 7-8
Main Pin 8
R

24vac from transformer
UCB Main Pin 1
Smoke Shutdown A
Smoke Shutdown B
Remote Shutdown A
Remote Shutdown B
Phase Monitor (PMR) A(24v)
PMR B(CONT)
Main Pin 7
LSM Input
LSM Output
Main Pin 8
R

Example 2: Ecoblue with LSM

You now have “R!”

The Danger of Carbon Monoxide

Mon, 09 Mar 2026 17:04:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

The Danger of Carbon Monoxide

Carbon Monoxide is a colorless, odorless, tasteless gas that can be extremely dangerous and even deadly. Because you cannot see or smell it, people often don’t realize they’re being exposed until symptoms appear.

Why Carbon Monoxide Is Dangerous

Blocks oxygen in the blood : CO binds to hemoglobin much more strongly than oxygen, preventing oxygen from reaching vital organs.
Starves the brain and heart of oxygen : This can quickly cause unconsciousness, brain damage, or death.
Hard to detect : Since it has no smell or color, people may be exposed without warning.

Common Sources in Homes

Carbon monoxide is produced when fuels burn incompletely. Common sources include:

Gas stoves and ovens
Furnaces and boilers
Fireplaces and wood stoves
Gas or charcoal grills used indoors
Running cars in garages
Portable generators
Gas water heaters

Symptoms of Carbon Monoxide Poisoning

Early symptoms often feel like the flu:

Headache
Dizziness
Nausea or vomiting
Weakness
Shortness of breath
Confusion

More severe exposure can cause:

Chest pain
Loss of consciousness
Seizures
Death

Who Is Most at Risk?

Children
Elderly people
Pregnant women
Pets (often show symptoms earlier)

How to Prevent Carbon Monoxide Poisoning

Install CO detectors on every level of your home.
Never run a car in a closed garage.
Do not use generators or grills indoors.
Have heating systems and chimneys checked yearly.
Keep generators at least 20 feet away from doors and windows.

What To Do If You Suspect Exposure

Get outside into fresh air immediately.
Call emergency services.
Seek medical attention.

Even small amounts over time can be dangerous, so prevention and detection are very important.

June 10, 2026

Diagnosing and Fixing Fault Code 44 on FE4 or FE5 Infinity Evolution Fan Coils

Mon, 09 Mar 2026 16:10:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Diagnosing and Fixing Fault Code 44 on FE4 or FE5 Infinity Evolution Fan Coils

Have you ever had a fault code 44 on a FE4 or FE5 infinity or evolution fan coil? Do you know what it means?

The explanation is actually very simple. Fault code 44 indicates a blower motor communication fault. This means the fan coil control board is unable to communicate with the blower motor.

When this code appears, the issue will always be related to one of three components:

The fan coil control board
The wiring harness
The blower motor

How do we trouble shoot this fault code? This article offers a simple series of troubleshooting options to help determine what may have gone wrong.

First confirm you are getting high voltage to the motor 208/230VAC. Check continuity on the wiring harness from the board to the motor.

Next check for 12VDC coming from the board to the motor. Check for 12vdc on wires 1 and 4 at the board, the best thing to do — because it is hard to back pin the plug — is the remove the plug from board and check directly at the board.

If you have 12VDC at the board the motor is bad. If you do not have 12vdc at the board the board is bad.

This information can be found in the installation manual and the service manual. If you have any troubleshooting questions, you can contact the Mingledorff’s Tech Service team with questions. Below are images from the service manual and the Mingledorff’s training guide that may help during the troubleshooting process.

June 10, 2026

It’s important to keep HVAC Tools Calibrated

Wed, 11 Feb 2026 16:14:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

It’s important to keep HVAC Tools Calibrated

Here’s why it matters in the real world:

Accurate diagnostics – Gauges, thermometers, manometers, and refrigerant scales that are even slightly off can lead you to misdiagnose a system. That’s how good units get blamed for bad reading.
System efficiency – Incorrect measurements can mean improper refrigerant charge, airflow, or combustion settings, which kills efficiency and drives energy costs.
Equipment protection – Overcharging, undercharging, or misadjusting based on bad data can shorten compressor life and damage components.
Safety – Combustion analyzers, gas leak detectors, and pressure tools need to be spot-on to catch dangerous conditions like CO or gas leaks.
Code compliance & liability – Many manufacturers, inspectors, and warranties assume calibrated instruments. Bad reading can put the tech (and company) on the hook.
Professional credibility – Customers trust numbers. Consistent, accurate readings make you look sharp and confident instead of “guess-and-check.”
Best practice:
Calibrate on a schedule (often annually, sometimes more for heavily used tools)
Check zero and baseline readings regularly
Store tools properly—drops, heat, and moisture mess with accuracy fast

In short: uncalibrated tools -bad decisions with confidence. Calibrated tools keep systems efficient, customers safe, and callbacks low.

Keeping HVAC tools calibrated is a big deal; it’s one of those behind-the-scenes things that quietly makes or breaks a job. Here’s why it really matters:

1. Accuracy-Doing the Job Right

HVAC work depends on precise measurements—temperature, pressure, airflow, voltage, refrigerant charge; you name it. If your gauges or meters are off, even a little, you can:

Over- or under-charge a system
Misdiagnose problems
Set controls incorrectly

That leads to poor system performance and unhappy customers.

2. Efficiency and Energy Savings

Uncalibrated tools can trick you into thinking a system is running fine when it’s wasting energy. Proper calibration helps you:

Tune systems to manufacture specs
Improve efficiency
Lower energy bills for clients

And honestly, customers notice when their bills drop.

3. Preventing Equipment Damage

Wrong readings can cause serious harm, like excessive compressor wear or improper airflow that stresses components. Calibrated tools help protect:

Compressors
Motors
Heat exchangers
Refrigeration systems

Fixing a mistake is way more expensive than calibrating a tool.

4. Safety First

HVAC techs deal with electricity, pressure, and sometimes combustible gases. Inaccurate instruments can put you at risk by:

Misreading voltage or current
Failing to detect dangerous pressure levels
Overlooking gas leaks

Calibration isn’t just professional; it’s personal safety.

5. Compliance and Professional Standards

Many manufacturers, codes, and regulations expect calibrated instruments. Staying on top of calibration:

Helps meet industry standards
Protects your license or certification
Build trust with inspectors and clients

6. Professional Reputation

Nothing kills credibility faster than repeated callbacks. Calibrated tools help you:

Get it right the first time
Reduce rework
Look sharp and competent

Bottom line: calibrated tools mean accurate work, safer jobs, better efficiency, and fewer headaches. It’s one of those habits that separates a decent tech from a great one.

June 10, 2026

...and not just for the “by-the-book reasons

The new Carrier 27VPA9

Wed, 11 Feb 2026 15:38:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

The new Carrier 27VPA9

This new unit is a noncommunicating variable 5 speed performance line heat pump with InteliSense technology, 19 seer2. Sizes range from 2, 3, 4 and 5 ton all the units are 35″ square. This heat pump will pair great with the FT5 fan coil and the new carrier smart thermostat, all of these are InteliSense capable units. Like all our Carrier and Bryant units, it does use R-454b puron advanced.

The heat pump is a cross between the 2 stage performance and the old 18 seer1 5 stage units with a little 23 seer2 mixed in with it. What we know so far about the unit is it wires up just like a regular 2 stage unit using Y1 and Y2 for staging, compressor speeds are based on outdoor temperature and demand from Y1 and Y2. Ie., in cooling mode if it is cooler outside and a call for Y1 is given, it will run lower compressor speeds. If it is hotter out and a call for Y1 and Y2 is given it will run higher compressor speeds and the same for heating mode based on outdoor temps and demand.

Open up the service panel and it will look some what familiar with a PCM and a VFD inside. This is where its mixed in with the old 5 speed and a 23 seer2 unit. Again this will wire up like normal 2 stage unit. The unit has 8 DIP switches for setting up testing and trouble shooting the unit. The PCM has a 5X7 matrix display to show fault codes and running info. The fault codes look a lot like the 23 seer2 units with a main code and a sub code. The unit has thermistors and pressure transducers on board just like it’s big brother Infinity unit for testing and trouble shooting the unit. You will have to log into the portal to see this info.

All of this info can be found in the installation manual and product data manual. Please refer to the slideshow below for guides on acronyms used in this article, diagnostic codes, and more.

June 10, 2026

This article is only in reference to models: TSTATCCEWF-01 & TSTATBBEWF-01.

Wiring of a VFD Fan Board at the J1 and J2 Plugs to VFD drive and to CTRL board

Wed, 11 Feb 2026 15:37:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Wiring of a VFD Fan Board at the J1 and J2 Plugs to VFD drive and to CTRL board

When you get a new VFD drive and want to install it and you see that the other one was already taken out by someone else and you are not familiar with the wiring of the drive then this will help you get the basic wiring out of the way for the specific drives listed below. By doing this you will prolong the life of the motors and equipment by using the VFD drive vs bypassing the drive which we do not recommend!

If for any reason you decide to bypass the drive, then you must follow Carriers temporary bypass instructions on Figure 4 and 5 of this article. The purpose of the bypass instructions is to avoid damaging the motors that do not have internal motor protection inside them.

NOTE: Use CTRL Button on keyboard plus your mouse wheel to increase or decrease image sizes on the Figures below.

If you notice on Figure 1 is a graphic to give you an idea of what is happening inside the board. The 24vac signal from the Control Board determines if it is a G/Y1 for low speed at 40hz or Y2/W for High speed at 60hz.

When the 24vac (AC) signal comes into the J1 Plug from the Control Board or CTB, it energizes the relays on the board to allow the 24vdc (DC) voltage that is generated by the VFD drive to allow the voltage through the pink wire on 24DVC on the J2 plug and then goes through the yellow wire which is Low or the white wire which is High on the relays as pictured in Figure 1, which then determines which speed the drive will run at. The settings of the drive then determine the speeds setup for it to run. In this case we used 40hz for Low speed and 60hz for High speed. If the drive is wired incorrectly then you will have issues with it working properly.

The next photo shows locations of where the wires go and the terminal numbers per drive you are using. But for this example we are staying with the ACH180 Drive.

June 10, 2026

Figure 1

The picture below shows you that the ACH180 Drive 24vdc pink wire goes on Terminal 21.

If it was an ACS320 Drive then it would go on Terminal 9.

In Figure 3 below, it shows the blue connection terminal block on the drive on the right.

Figure 3

View of an actual ACH180 Drive to see the color terminals

Troubleshooting Codes 25-XX

Tue, 13 Jan 2026 19:53:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Troubleshooting Codes 25-XX

Have you worked on the new 20, 21, and 23 SEER2 units and encountered a fault code 25-XX (for example, 25-61)?

Fault code 25 indicates an invalid model plug. On the newer units, however, it can mean more than just a missing model plug. “Invalid model” may indicate that the unit does not recognize what it is, or that it believes it is a different capacity or type than it actually is—for example, a 3-ton AC being identified as a 5-ton heat pump. This fault will be displayed on the PCM (Primary Control Module), which is the main control board for the unit.

The fault consists of a main code (25) and a subcode (such as 61). Common model-related fault codes include 25-24, 25-61, 25-62, and 25-63.

These new units do not require or use model plugs from the factory. They are programmed at the factory with the correct model and serial number. A model plug is only needed if you are replacing a PCM or if the board has lost its programming.

June 10, 2026

So what if you don’t have a model plug? Here’s a useful trick.

In the Technical Service Group, we have seen both brand-new units that didn’t recognize themselves out of the box and existing units that lost their model information, but the technician does not have a model plug on hand. In this case, you can use the DIP switches to reidentify the unit.

With power on, turn DIP switch number 4 on. The PCM will detect the size of the VFD and begin scrolling available unit sizes on the 5×7 dot matrix display. For example, on a 3-ton heat pump, it will scroll “36K AC” and then “36K HP.” When “36K HP” appears, turn DIP switch number 4 off and power-cycle the unit. This will lock in the correct BTU and type of unit.

When power is restored, the display will show “36K HP” for approximately two minutes, confirming the setting has locked in.

For any questions regarding this process, you can refer to the unit’s Service Manual, or contact the Technical Services Group for further guidance.

Below is an example of the guidance you may find in the service manual.

The Importance of Reading the Installation Manual Before Installing HVAC Equipment

Tue, 13 Jan 2026 19:52:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

The Importance of Reading the Installation Manual Before Installing HVAC Equipment

Installing heating, ventilation, and air conditioning (HVAC) systems require precision, knowledge, and attention to detail. While many technicians rely on experience and training, one crucial step that is sometimes overlooked is reading the manufacturer’s installation manual. The manual is not just a formality, it is an essential guide that ensures safety, efficiency, and system longevity.

Ensuring Proper Installation

Each HVAC system is designed with specific requirements for electrical connections, refrigerant lines, airflow, clearances, and mounting. Even systems from the same manufacturer can have variations between models. The installation manual provides step-by-step instructions tailored to that particular unit, ensuring components are installed correctly. Skipping or misinterpreting these instructions can lead to performance issues, mechanical failures, or warranty voids

Protecting Warranty Coverage

Manufacturers’ warranties often depend on proper installation according to their specifications. If a technician installs the unit incorrectly or fails to follow prescribed procedures, any resulting damage may not be covered under warranty. Reading and following the manual helps protect both the installer and the customer from costly repairs or replacements later on.

Ensuring Safety

HVAC systems involve high voltage electricity, refrigerants under pressure, and combustion in some cases. Improper installation can cause electrical hazards, gas leaks, or poor ventilation—all of which pose serious safety risks. The manual provides critical safety warnings, wiring diagrams, and start-up procedures designed to prevent accidents and ensure compliance with local codes and safety standards.

Maximizing System Efficiency

Manufacturers design their equipment to operate at peak efficiency when installed correctly. Incorrect refrigerant charge, poor duct connections, or improper sensor placement can reduce system performance and increase energy consumption. Following the installation manual ensures the system operates as intended, saving energy and improving comfort for the end user.

Reducing Callbacks and Maintenance Issues

A rushed or improperly installed HVAC system can lead to frequent service calls, customer dissatisfaction, and lost time for the technician. Reading the manual and following best practices during installation helps prevent common mistakes—such as incorrect airflow direction or improper drain line setup—that can lead to system malfunctions.

Staying Current with New Technologies

Modern HVAC systems often include advanced electronics, smart thermostats, variable-speed motors, and complex control systems. These technologies evolve quickly, and even experienced technicians can miss updates if they skip the manual. Reading the latest installation guide ensures familiarity with new features, programming steps, and troubleshooting methods.

Reading the installation manual is not just a recommendation, it’s a professional responsibility. It ensures that HVAC equipment is installed safely, performs efficiently, and complies with warranty and code requirements. Whether you’re a seasoned installer or a new technician, taking the time to read and understand the manual is one of the simplest yet most effective ways to guarantee quality workmanship and customer satisfaction.

June 10, 2026

Diagnosing and Correcting a Heat Pump That Will Not Enter Defrost

Tue, 13 Jan 2026 19:40:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Diagnosing and Correcting a Heat Pump That Will Not Enter Defrost

Imagine that you receive a call from a customer stating that their heat is not working.

Upon inspection you find that the heat pump is not going into defrost mode. You cannot initiate defrost mode by jumping speed up terminals. The outdoor fan continuously runs. You notice that the outdoor coil ices up and never goes into defrost mode. There is no voltage on T1 to Common or Ground. What could be happening?

An Example of a Properly Wired Contactor Vs and Improperly Wired One

June 10, 2026

The voltage comes from the Y terminal and goes through a few safeties then the voltage goes to the T1 terminal. Please refer to the connection diagram above.

If power is on the T1 terminal, then it should be capable of going into forced defrost or able to run normally by the timer and defrost thermostat.

When there is no power on the T1 Terminal the outdoor fan runs continuously. With no power on T1, it will not allow the defrost process to happen which, in turn, would energize the relay and change the NC set of contacts to “NO” thus shutting down the outdoor fan.

Typically, the reason this happens is because it is mis-wired at the contactor. The brown wire should be on one side of the contactor by itself. The rest should go on the other side.

The two images below shows a board with the T1 terminal on it so you can see the locations of this specific board. In the picture on the right, you can see it is mis-wired. The blue needs to be on the other side of the contactor coil.

When the 24vac is on T1 and there is a call for defrost then it can energize the relay to shut off the fan.

If you have further questions or need assistance troubleshooting, refer to the units service manual or contact Mingledorff’s Technical Service team.

ICP Furnace Showing 80% Limit Fault

Mon, 08 Dec 2025 15:52:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

ICP Furnace Showing 80% Limit Fault

Most gas furnaces have several safety limits, main limits, roll-outs, 80%’s will have a DSS (Daft Safety Switch) These safety switches are look at by the CPU on the main control board all the times.

An ignition fault is a common fault with a furnace from time to time. It could be caused by several things. An ICP 80% furnace will try to light a total of four times before the furnace locks itself out on a Code 6.

This fault can happen during the beginning of a trial heating call or after the furnace lights if it loses flame sensing. If a furnace loses a proven flame before the blower cycles on, the blower will run for the selected off-delay time set on the control board.

These are the things that need to be checked if you have this fault.

First: check that the green/yellow wire on the gas valve is connected to the sheet metal cabinet to ensure there is a good ground to the control board and gas valve. Make sure the gas shutoff is turned completely on, and also verify the gas valve is turned on.

Next: check the gas inlet and manifold pressure. A furnace with low pressure will have problems lighting from time to time due to under-firing and can light if other gas appliances are not on at the same time. Low inlet pressure can also be caused by the gas line not being large enough to supply the furnace with gas. Check your line size to ensure you have a properly sized line.

After that, the flame sensor is also an item that will need to be checked. Specifically, the microamps. A normal reading will be between 4.0 and 6.0 microamps. If there is oxide buildup on the flame sensor, clean it with fine steel wool.

Lastly, check the crossovers to ensure adequate flame crossover on the burners. This will cause the flame not to reach the flame sensor.

For more information check the installation manual that is supplied with the product as some models will also have a troubleshooting manual.

Sources, Links & Media:

HVAC Partner Installation Manual.

June 10, 2026

Indoor TXV Failure in Heat Mode

Mon, 08 Dec 2025 14:49:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Indoor TXV Failure in Heat Mode

This article is in reference to Residential Heat Pumps.

Everyone in the HVAC industry knows that the indoor TXV does not do anything in the heat mode, right? -or does it do something? Let us discuss it!

June 10, 2026

If this bypassing check valve fails, then the refrigerant will slow down/ or stop in the indoor coil. Diagnosing this uses the liquid line pressure.

Typically, there are two ways the bypassing check valve fails in Heat Mode:

Completely shut.
This causes the head pressure (large vapor pipe) on the unit to rise and trip the high pressure switch open and/or the low-pressure switch will open because the unit will be trying to pump down.
True suction may be pulling down like a pump down.
If you put a gauge on the liquid line (small pipe), then you would see the pressure is extremely low and mimicking the suction pressure.
Sometimes there is a temperature drop across the indoor TXV.
Liquid line at the outdoor unit will be colder than the indoor temperature.
Partial shut. This is a little harder to notice and diagnose.

This will cause the outdoor metering device (piston or TXV) to freeze up and typically misdiagnosed: either as restricted or the unit being low on charge.
The suction pressure will be extremely low for the conditions outside.
The discharge will be higher than normal for the indoor conditions.
There will be a temperature difference across the indoor TXV.
Liquid line at the outdoor unit will be colder than the indoor temperature.
If you put a gauge on the liquid line, you would see the pressures favoring or being close to the suction pressures need to be.

So, what SHOULD your liquid line pressures be in heat mode?

The liquid line pressures in heat mode should favor or be near (ish) the head pressure. As you know, the head pressure is variable depending on indoor and outdoor temperatures. Unfortunately, there is no statistical data provided by any manufacturer for what the liquid line pressures should be in heat mode. However, we do know what they should not be. They should not be pulling down and looking like suction pressures nor anywhere close to those pressures. The liquid line TEMPURATURE should not be colder than the indoor dry bulb temperature of the home.

Remember, if the bypassing check valve in the TXV is doing its job, it should freely flow refrigerant right through the valve with no temperature drop across it.

In the Heat Mode, the reversing valve reverses the refrigerant flow through the system. Now, the indoor coil is the condenser, and the outdoor coil is the Evaporator. This means the outdoor coil is COLD due to a metering device like a piston or TXV, and the indoor coil is going to be HOT. Since the refrigerant is flowing backwards it comes right out the discharge of the compressor and goes to the indoor coil with HOT gas. This gas passes through the indoor coil nonstop without using a piston nor TXV and gives up heat to the air in the home; when heat is removed from this gas, it turns into a warm liquid.

In the description laid out in the paragraph above, you see that the indoor TXV has no job in the Heat Mode, so you think. It does have a job though; its job is to “bypass.” There is a bypassing check valve built into Heat Pump TXV’s. If this bypassing check valve fails, then the TXV cannot do its “bypassing” job.

What would this failure look like, or how would this look like on a system?

Compressors Problems & Troubleshooting

Mon, 08 Dec 2025 14:18:00 GMT

Anthony Coker

Technical Services Manager Southeast District

Compressors Problems & Troubleshooting

Compressors are the heart of the refrigeration system. It creates the pressure difference to move the refrigerant through the system. Compressor checks are normally not done unless when troubleshooting the unit. Since compressors are expensive and their replacement can be time consuming, you need to be sure it is bad before replacing it. There are certain ways to identify compressor problems and measure the compressor windings and identify unmarked terminals.

Shorted Dual Run Capacitor

June 10, 2026

Also, low incoming supply voltage to the compressor which can be caused from poor contacts on a contactor. The run or start capacitor to the compressor could be open or weak allowing the appearance of a seized-up compressor.

Compressor testing is needed to determine what is wrong and what may have caused the problem. There are some compressor symptoms that appear to be a compressor failure but are caused by another part on the system. Above is a brief example of compressor problems and how to check windings on a good compressor. There are a lot more system related problems that, if not corrected, can cause mechanical and electrical failure of a compressor.

Sources:

HVAC Servicing Procedures

Pictures from XOI & Internet Images

One example would be a seized compressor. The compressor draws locked rotor amps and hums for several seconds and the internal overload opens up. This can be caused by a mechanical or electrical problem within the compressor or by an external electrical problem. The unequaled refrigerant pressures can cause a compressor to pull lock rotor amps and appear to be seized.

The scenarios above give the appearance of a seized compressor but are not and are repairable without replacing the compressor. If the mechanical workings of the compressor fail or brake causing a sized up compressor the compressor will have to be replaced.

Another example would be low or no capacity. Compressors have valves, rings and plates that seal between the high – pressure and low – pressure sides of the system and the compressor. If either is damaged, correct operating pressures can never be developed. This condition can be checked two ways, one using pressure gauges and an amp meter. Using the pressure gauges, you would notice that the suction pressure is excessively high and the discharge pressure is excessively low, the compressor most likely has an internal problem that allows pressure to leak past the high and low sides of the compressor. Using the amp meter, you would notice a considerably lower than normal amp draws. The compressor would have to be replaced.

Checking Compressor Windings

If you have ever had a single-phase compressor that the terminals were not marked there is a fairly simple way to too identify which terminal is Common (C), Start (S), and Run (R). First follow all safety precautions, make sure power is off and if the compressor is in a pressurized system, do not place the meter probes directly on the compressor terminals. If the terminals are damaged and the system is pressurized, disturbing them to take readings could cause them to blow out, causing injury. Second remove the three compressor wires from all components. Then using your meter measure across the three compressor leads to find the two terminals that have the highest resistance reading. The remaining terminal is the Common (C) winding terminal. Next put one of your meter leads on common that was just found and the other lead on one of the other two remaining terminals to find the next highest resistance measurement. This is the Start (S) winding terminal. The last remaining terminal is the Run (R) winding terminal.

Terminals C to R have the lowest resistance.
Terminals C to S have the next highest resistance.
Terminals R to S have the highest resistance.
Resistance from C to S + Resistance from C to R = Resistance R to S.
Example: C to S is (3.0) and C to R is (0.5) and R to S is (3.5) so, (3.0 + 0.5) = 3.5

R-454B & R-410A Refrigerants: Are They The Same?

Wed, 19 Nov 2025 15:02:00 GMT

Anthony Coker

Technical Services Manager Southeast District

R-454B & R-410A Refrigerants: Are They The Same?

You have probably gone to classes, listened to podcast or read articles about the phase out of R-410A, and the replacement refrigerant R-454B that will be in a lot of new equipment. R-454B is not the only replacement refrigerant, as some manufactures will use other refrigerants in their equipment. In this article R410-A & R454-B will be the two refrigerants that will be compared.

Let’s look at what is in the make up of the two refrigerants. R-454B is a blend of 68.9% R-32 & 31.1% of R-1234yf. R-32 is used in small to large equipment that heat and cool. R-1234yf is used in some of the new cars being manufactured. R-410A is a blend of 50% R-32 & 50% R-125. R-125 is used in fire extinguishers, which helps reduce the flammability of the R-32 it is mixed with. Just because R-410A has a gas that helps reduce its flammability does not mean it can’t be ignited. Scientist have a procedure for testing the flammability of refrigerants. They use a glass flask of electrodes and they interduce air and the refrigerant into the flask. Once the refrigerant is ignited, it has to stay in a 90-degree V-shape marked on the flask. Then the refrigerant is classified as being flammable or not flammable. Class 1 is not flammable and Class 2 is flammable. But R-454B did not fall into the Class 2 flammable category. The flame spread was a lot slower and fell just outside of the 90-degree testing range, so a new class was developed for it and it is Class 2L (Lower Flammability). There are also letters that classify the toxicity of the refrigerant. A is for lower toxicity and B is for higher toxicity. R-454B is an A2L lower flammability refrigerant and R-410A is an A1 Non-Flammable refrigerant.

Operating Pressure vs. Saturated Temperatures

June 10, 2026

Because the refrigerants are blended with other refrigerants, you have to look at the glide or different points that the two refrigerants change state while in the equipment. R-410A had a temperature glide close to 1 degree and R-454B temperature glide is a little over 2 degrees. Because of this very small difference, it is ok to top off the refrigerant charge if the unit is a little low. R-410A had little to no capacity loss by doing this. R-454B, depending on the amount lost and added over time, could see a slight capacity loss. Below is a chart showing removing 50% of the charge 5 times and adding it back 5 times. There is a slight loss in capacity.

Another difference between the two refrigerants is it’s GWP (Global Warming Potential). The EPA (Environmental Protection Agency) has set the base GWP at 700, R-410A’s GWP is 2088 and R-454B has a GWP of 466, which is significantly lower. Some other differences are the pressures and temperatures. Below is a chart showing pressures verses saturated temperatures

There are differences in the two refrigerants, but there is not a big difference. One difference is the GWP, R-410A is 78% higher than R-454B. There is not a great difference between the pressures and temperatures. But R-454B is a lower flammability refrigerant and will need safety devices added to an HVAC system incase there is a refrigerant leak. There will be different metering devices in the equipment also. R-410A and R-454B can not be used as a substitute for one another.

Sources:

Chemours

Dr. Chuck Allgood with Chemours

Classes of Refrigerant

Flam Spread in the testing flask

R-410A

R-454B

Speedy Maintenance: Split Heat Pump Fall Check Sheet

Wed, 19 Nov 2025 15:00:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Speedy Maintenance: Split Heat Pump Fall Check Sheet

June 10, 2026

1. Arrival

Upon arrival greet customer
Change filter.
Turn the thermostat off AND RECORD SETTINGS.

2. Indoor Unit

Locate air handler.
Turn power off.
Check capacitor. (if available)
Clean indoor coil.
Flush drain line
Inspect blower wheel scoops.
Inspect for burnt/loose wires.
Turn power on.
Verify amount of electric heat (KW) & proper amperage draw for that amount.

3. Outdoor Unit

Locate condensing unit.
Turn power off.
Check capacitor. (if available)
Inspect contactor points.
Inspect for burnt/loose wires.
Clean outdoor coil.
Turn power on.
Turn unit on.
Typically, in cooling mode when above 70f outside.
In heating mode when below 70f outside.
Tests defrost cycle.
Either short defrost pins or use ice water on defrost sensor.
Let unit RUN: 15 MINUTES MINIMUM.
While waiting on units to stabilize, clean up and start Records/ Invoicing.
Check refrigerant pressures.
Record Delta T.

4. Facing Customer for repairs (skip if no repairs needed)

Talk to and discuss problems with the customer.
Have prices ready.
Make repairs if needed.
Verify unit operation after repairs.

5. Records/ Invoicing

When filling out invoice records, write down the following:
model/serial numbers of all units checked.
outdoor/indoor temperatures.
Delta T.
refrigerant type, refrigerant pressures.
Including subcool and superheat.(if in cool mode)
Amount of strip heat checked.
MAKE NOTE IF CUSTOMER DECLINES ANY RECOMMENDED REPAIRS.
Notes on invoices are a good CYA policy.

6. Completion/ Signature

Return thermostat to previous mode and setpoint unless customer States otherwise.
Get the invoice signed and collect payment.

Today’s article is a guideline to help new technicians develop a speedy routine while doing fall maintenance on heat pumps. We designed this guide to help make the best use of your time while there. If followed, it will accommodate things such as preventing kneeling in water while checking the outdoor electrical, giving plenty time for the evaporator coil-cleaner to drain, and utilizing the stabilization time, leaving disconnects off, plus more. This guide is one of the best sequences to deliver speedy maintenance while providing a top-tier inspection and cleaning.

Why am I getting a 25 Fault Code?

Wed, 19 Nov 2025 14:56:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

Why am I getting a 25 Fault Code?

When a Bryant furnace displays Error Code 25, it indicates that the control board has detected a configuration mismatch between the furnace model and the settings or components used to identify it. This fault commonly arises from issues with the model plug (PL4), incorrect DIP-switch configurations, or incompatibility in replacement control boards or firmware versions. Although the alert can appear serious, it is typically related to identification or setup errors rather than a mechanical failure. The following article provides a detailed explanation of the possible causes of Code 25 and outlines systematic troubleshooting steps to accurately diagnose and resolve the issue.

What Does Code 25 Mean?

1. Model Plug (PL4) Missing or Incorrect

Bryant furnace control boards use a model plug (sometimes called PL4) — it’s a small jumper/resistor configuration that tells the control board what model of furnace it’s connected to.
If the model plug is missing, or if what’s installed doesn’t match the furnace model, you’ll get this code.
In some cases, if the furnace was repaired and the control board replaced, the new board may not have the correct plug installed.

2. DIP Switch Settings Incorrect

There are dip switches on the control board (sometimes labeled SW1). Certain switches (notably SW1-1 and SW1-6) are used for service/testing, and if they’re left “ON” in normal operation, it can trigger this error.
Sometimes both switches are ON when they shouldn’t be, which causes a configuration error.

3. Wrong Control Board or Firmware Version

If a replacement control board was installed, but it’s not the correct type (or doesn’t have the right software/firmware), it can “think” it’s controlling a different model than what’s actually installed.
For example, manuals mention needing a modulating furnace control with a certain software version (e.g., V17 or later) or you’ll get this fault.

4. Model Plug Changed While Powered

In some Bryant/VFD systems, if the model plug value changes while the system is powered, the board flags a “model plug changed” error.
The system may reject the change, or go into a lockout if the plug doesn’t match expected values.

June 10, 2026

What to Do (Troubleshooting Steps)

Here are some recommended steps to try and resolve Code 25:

1. Power Down Safely

Turn off power to the furnace before touching the control board — safety first.

2. Check the Model Plug (PL4)

Locate the PL4 “personality” plug on the control board.
Make sure it’s physically present and seated correctly. Some technicians say to remove it and re-insert it to ensure a good connection.
Confirm the plug matches your exact furnace model. If you have documentation/manual for your furnace, you can cross-reference the correct model plug.

3. Inspect / Reset DIP Switches

Look at the SW1 bank of dip switches. Turn SW1-1 and SW1-6 OFF (if they’re on), unless they’re specifically needed for a test mode.
After adjusting, power the furnace back on and see if the error clears.

4. Reset the Control Board

After making corrections, remove power again, wait a moment, then restore power. This can force the board to re-read the model plug and the switch settings.
If the code “25-24” or similar (model changed) was triggered, sometimes removing and reinstalling the plug + power cycling clears the code.

5. Replace the Control Board (if needed)

If everything looks correct (plug in place, switches correct) but the error persists, it may be a faulty control board: either a bad connection/solder, or the board isn’t recognizing the plug.
Make sure any replacement board is correct for your furnace model and has the right firmware/software.

As you can see, there are only a limited number of issues that will trigger a Code 25 fault, and most of them relate directly to how the control board identifies the furnace model. Ensuring that the model plug is present and that its resistance value matches the specifications for your furnace is one of the most important steps in resolving this error. Keep in mind that on newer furnace designs, the traditional physical model plug may no longer be used; instead, the model information may be programmed directly into the control board. Because of this, verifying that the correct board and firmware version are installed becomes even more critical. By confirming these key components and settings, most Code 25 faults can be diagnosed and corrected efficiently.

How to Program an NFC Control Board

Wed, 15 Oct 2025 14:43:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

How to Program an NFC Control Board

When replacing a control board equipped with Near Field Communication (NFC) capabilities, it’s critical to ensure that the new board is correctly programmed before attempting to operate the furnace. Each model is designed to operate with a specific Model Program Number, which defines the configuration and control logic for that unit. Programming the new control board with the correct program is essential for safe and proper furnace function.

Failure to program the board, or programming it with the wrong Model Program Number, can result in improper operation, system faults, or even damage to the furnace components. Always refer to the Model Program Number listed on the furnace rating plate, typically found on or near the burner compartment door. This number is unique to the furnace model and ensures compatibility between the control board and the rest of the system.

This article will walk you through the necessary steps to program a new NFC-enabled control board accurately using a simple step-by step guide.

The board can be programmed before it’s installed in the unit or after you have installed it. It is important to note that if you are choosing to program the board after installation, you must make sure that it is disconnected from power prior to beginning the programming process.

You will program the board using the Open Service APP. Below, you will find the QR codes for both the Carrier and Bryant versions. If you are on mobile, you may click the QR code to be taken to the app store. Once downloaded, you will be prompted to sing in. If you don’t have an HVAC Partners ID, you may continue as a guest.

June 10, 2026

This guide should help you program your new furnace board. remember, the board may be out of the furnace or already installed, but it must be disconnected from the power source. Should you have any questions, please do not hesitate to contact the Technical Services Team for further guidance.

Once your board is programmed, you may adjust the blower speed while the furnace is running. For guidance adjusting the blower motor speed, reference our previous article titled: “ How to Change the Blower Speed on an 820TB Furnace with a HKFZ NFC Furnace Board. “

Bryant Open Service App

Carrier Open Service App

1. After you log into the app, you will connect to the furnace.

2. Choose “Replace Control Board”

3. Enter the serial number of the furnace and press “continue.”

4. The Model number should show alone with serial number at top of screen.

5. After entering this information, you will be ready to scan the information into board using the NFC compatibility feature. Hold you phone level to the board, near the phone’s antenna.

Note: iPhone antennas are near the top edge of the phone.

OS antennas are near the middle of the phone.

The power to the board MUST be off during this time.

5. Once the process is complete, a check mark will appear on you screen. If this does not appear, begin these steps again.

Diagnosing a Broken Common Wire to the Outdoor Unit

Tue, 14 Oct 2025 18:08:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Diagnosing a Broken Common Wire to the Outdoor Unit

If you were to remove or break the common wire to a device, such as an outdoor unit what would happen?

June 10, 2026

When looking at most control schematics, notice that the “return wire”, otherwise known as Common, is also connected to ground at the transformer. If this common wire from the indoor to outdoor unit is broken, the electrical current cannot make a full connection which results in an incomplete path for the voltage/amps. When checking for voltage on (Y, O, and Common) to ground, your meter is showing Voltage “Potential” to ground. This is due to the connection of the Common wire at the transformer to ground. Under normal circumstances, if the common wire were not broken, a reading of Ø Zero VAC would be read from common to ground. This proves that common and ground are tied together at the indoor transformer, and function as one single connection. This too can be said if the common wire at the outdoor unit were to be connected to ground, as it would then complete the electrical path through the ground circuit. Bear in mind this is not for a permanent repair but merely just for testing.

Remember, checking for voltage AC to ground is not the same as checking AC to Common. Always check to common, not ground.

This article is in reference to residential HVAC equipment but can apply elsewhere.

You would think that a broken wire to an outdoor unit would be easy to find, right? Well, it all depends how you troubleshoot and how you analyze the results of your troubleshooting.

HVAC technicians know that it takes two (24VAC) wires to energize standard HVAC Parts (contactors, T-stats, relays, etc.). In layman’s terms: one wire is a “power wire” which is “sending” voltage to a device; while the other wire is the “return wire” AKA: “Common Wire” that completes the loop back to the power source [the transformer].

Great question! If a thermostat were to connect R to Y and R to O, then 24VAC should be sent to the outdoor unit. As 24vac on Y comes into the unit, it will pass through all the safety switches and land on the contactor; at the same time 24vac on the O wire will be sent out and fed to the reversing valve coil. If the common wire is broken from the indoor unit to the outdoor unit, then these devices will not do anything. They will sit there looking and acting deenergized.

Let’s run through a simple cooling scenario. Typical heat pump HVAC systems supply 24 VAC signals to Y for the main call and O in cooling mode to engage the reversing valve.

As a technician, when you check the contactor and reversing-valve coil wires for VAC to ground, you will have 24vac. If you check your common wire at the outdoor unit to ground, you will also have 24vac. STRANGE, right?

Why is this? Why would the Y and O wires have 24VAC, AND the common wire have 24VAC when these devices are deenergized?

Puron Advanced (R-454B) Refrigerant Dissipation Board Flash Code 13

Tue, 14 Oct 2025 17:59:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Puron Advanced (R-454B) Refrigerant Dissipation Board Flash Code 13

June 10, 2026

With the changing of the new refrigerant, new controls have been added for safety incase of a refrigerant leak, the Refrigerant Dissipation Board (RDB). This board has 13 flash codes but number 13 is the one that is going to be discussed. Different main control boards will connect to the RDB differently. The equipment that uses a Unit Control Board (UCB) will be discussed in this information. Some of the units are the 40RLA commercial fan coils and 50FEQ RTU units, these are just a couple that use the UCB board with the dissipation controls.

UCB

RDB

The flash code 13 description is the ( Fire / Smoke Override / G input signal is lost. Indicates another unit safety will override dissipation ). What actually happens is the RDB looses 24 volts to the board on connection 6 where the J1 connector plugs onto the RDB. There are several things that can cause the loss of 24v to this connection on the RDB. The 24v that leaves the transformer and travels into the UCB board through the main connector will go through the smoke detector, phase monitor, fan limit switch and safety relay built into the Eco Blue motor or the safety switch on the VFD drive on larger units. This path is also known as the safety chain circuit, if any of these controls interrupt the path of the 24v it will kill 24v to the UCB and not allow the unit operate and trigger the flash code 13.

If you get a call to a commercial job and the thermostat is blank and the RDB is displaying the 13-flash code. Look for any safety device that could have interrupted the 24v path that sends the 24v to the RDB connection 6 in the J1 connector. Also remember that the safety circuit in the Eco Blue motors and VFD drive is only closed when they have power.

Sources:

40RLA/S/Q 07-12, Installation, Start-up & Service Instructions / 3-2025

40RLA/Q/S*14-30, Installation, Start-up & Service Instructions / 3-2025

50FEQ*04-07, Installation Instructions / 11-2024

50FEQ*17-28, Installation Instructions / 7-2024

How to Change the Blower Speed on an 820TB Furnace with a HK42FZ112 NFC Board

Mon, 29 Sep 2025 15:27:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

How to Change the Blower Speed on an 820TB Furnace with a HK42FZ112 NFC Board

This article covers how to change the blower speed on furnaces equipped with the new NFC board HK42FZ112. After reading, you will understand the key features of the board and how to adjust the blower speed to meet your performance needs.

This furnace has a control board with a 3-digit LCD display. It boasts push-button navigation to simplify adjusting operation parameters, making diagnostics and service much easier when you are in the field. The control board must have power to use the display and push-button options. It comes pre-programmed by the factory with a Model Program Number, which is specific to each model. The operation settings are adjusted using the service app.

Follow these steps to access the menu that will allow you to rest your blower speed.

June 10, 2026

1. Press the “Menu” button on the control board. The LCD screen will display abbreviated codes. You can toggle through them by pressing the Menu button repeatedly. Below is the list of pre-programmed codes on the 820TB.

2. This is the Menu you will use to adjust the blower speed on any entry-tier furnace. “Flt” will be displayed on the LCD screen the first time you press it.

3. Press the Menu button two more times. Now, the display should show “CL”. This is where you have the option to adjust your parameters for cooling speed.

4. To adjust the blower motor speed, press the “Next Option” button. This will show the speed the motor is set to. To change the speed, press the “Next Option” button again. Keep doing this until you get to the speed at which you want the blower motor to run. Once the fan speed is selected, press the “Next Option” button to confirm. The display will show the confirmed settings. If any further adjustments are needed, press “Next Option” until desired settings are input.

Control Board Replacement

If the control board must be replaced, the new board must be programmed with the correct Model Program Number before the furnace will operate. Do NOT program the control board with a Model Program Number that is different than what is specified on the rating plate.

The control board may be programmed by either of these approved methods:

Use the supported mobile app to flash the model program onto the board using Near Field Communication (NFC). Scan the QR code on page 1 of the 820TB manual for more information and a link to download the mobile app.
Use the correct Super Plug (available from distributor / replacement component) for the control board to copy the correct model program onto the new board. Further details and instructions for these programming methods are provided with the replacement control board.

In conclusion, adjusting the blower speed on the 820TB furnace equipped with the HK42FZ112 control board is a straightforward process thanks to its intuitive LCD display, push-button interface, and NFC-enabled capabilities. By following the outlined steps, technicians can easily access and change the cooling speed settings to meet system requirements or customer preferences. Additionally, understanding the correct procedure for programming a replacement control board ensures proper operation and prevents configuration errors. With the use of the service app or the appropriate Super Plug, the 820TB blower system remains both versatile and service-friendly in the field.

Missing Serial Numbers on Infinity/Evolution User Interfaces

Mon, 29 Sep 2025 15:13:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Missing Serial Numbers on Infinity/Evolution User Interfaces

Reference this image if you are following the "unlocked" procedure option.

June 10, 2026

Have you ever noticed that (inside the software) some User Interfaces (UI) have serial numbers listed, and some don’t? Why is that and where are they? This article will show you exactly where to find those missing serial numbers on both locked and unlocked screens.

For starters, where can serial numbers be found?

Typically , the Model/Serial numbers of communicating systems can be found in the UI in two locations: 1 in the unlocked screens and 1 in the hidden service screens.

For the unlocked method, follow this path= Menu < WHITE hat* < Model Serial Numbers.
For the hidden method, follow this path= Menu < GREEN hat < Service Information < Model Serial Numbers.

*If you do not know how to make the white hat turn green, please refer to the UI install manual for this information*

When communication equipment is made, the original control boards (in them from the factory) have a model and serial number loaded into them. This way, when you install the equipment, you can see the model and serial numbers for all the equipment through the UI. However, only the original factory board can contain the serial number! If the original board is removed, then a “Service Board” would have to be installed in its place.

Service Boards, they look identical to the original board. These boards drive the equipment 100% the same as the original; the only thing different is they do not have a serial number encrypted into the software. When these boards are installed, they will rely on being told what their model number is by: model plug, selection of a model number on the screen, or use of a dip switch. This is all dependent on which and what type of unit the board is going on.

So, to sum all this up: If you look in the UI and a serial number is not listed for a unit, this means that it is not the original control board in it because it has been changed.

Reference this image if you are following the "locked" procedure option.

Setting the Electronic Model Plug on The Primary Control Module (PCM)

Fri, 26 Sep 2025 12:47:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Setting the Electronic Model Plug on The Primary Control Module (PCM)

June 10, 2026

The Primary Control Module (PCM) controls various functions of the outdoor unit. These functions are determined by the inputs the PCM receives and outputs it sends out. When this board fails and needs to be replaced the board needs to know what tonnage unit it is going into. The Carrier Green Speeds and Bryant Extreme variable speed units use these PCM boards that need the model plug configuration. Some models are the 27VNA HP’s, 26VNA A/C’s, 191VNA A/C’s, & the 290VNA HP’s models.

The PCM has been pre-programmed at the factory with an electronic model plug. This electronic model plug removes the need for a physical model plug to be installed into the PCM. The electronic model plug configuration establishes the, tonnage and type of unit. If the PCM has to be replaced or the model configuration is unknown, there are several ways to set the model configuration. The Infinity or Connex wall control, the Service Tech App, or the PCM dip switches can be used to configure the PCM.

To set the model configuration, you will have to enter the Menu Mode by setting the DIP switch #4 to ON at the PCM board. When DIP switch #4 is set to ON, a list of compatible PCM Model values will scroll across the marquee depending on the VFD model detected. When the desired PCM model shows on the marquee, turn DIP switch #4 to OFF. Here is an example, if a 5 Ton VFD model is detected; the list of compatible PCM models would be 60K-AC, 60K-HP, and NOCFG. To set the PCM’s model flip the DIP switch #4 on the PCM to OFF when the desired tonnage is being scrolled across the marquee. When a model is selected by setting DIP switch #4 OFF, the selected model is displayed on the 5×7 display for 2 minutes. A power cycle is then required for the model configuration to be established in the PCM memory.

Sources:

Infinity® Series Variable Speed Air Conditioner and Heat Pump with Greenspeed® Intelligence Using Puron Advance™ (R-454B) Refrigerant Service Manual / Edition Date: 05/25

The above is physical model plugs that can be ordered if needed to plug directly on to the PCM board.

An electronically set model configuration will take effect immediately. The PCM remembers the most recent valid model configuration detected at power-up, regardless of that configuration coming from an electronic or physical model plug. Model configuration is stored in the PCM’s memory so power cycles will not erase this information. A physical model plug at power-up takes precedence over a model configuration stored in memory. If a new valid model plug value is detected at power-up, the model configuration memory will be updated to that new value.

Just remember that when replacing the control boards that the physical model plug is not there and it will need to be programed from the PCM board, or Bryant/Carrier Tech APP, wall control, or a physical model plug.

How to Wire and Check a Dissipation Board

Mon, 18 Aug 2025 14:36:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

How to Wire and Check a Dissipation Board

In our last article, Understanding Active Dissipation , we covered the basic reasons why a system may have a refrigerant leak and how the board will operate during dissipation mode due to that leak. This month we will take a deeper look at how to properly wire {install} and troubleshoot the sensor itself on the FJ fan coils.

June 10, 2026

Next is the Dissipation Sensor. The sensor is a 4 pin 5vdc sensor with an 8ft harness. The sensor will be factory mounted in all fan coils and SPPs. The sensor will be located in the case coil boxing. If a cased coil is being installed, the sensor is NOT factory installed but does come included. Please be sure to check all packing materials to ensure the sensor and harness aren’t accidentally discarded.

Troubleshooting the harness connections is simple using the picture below to check for the proper 5VDC signal.

To be able to accurately troubleshoot anything, you must know where to start. The dissipation board pictured above, resides between the main board and the thermostat. This allows the dissipation system to actively control the unit during a dissipation sequence. This occurs starting at the wiring for the 8-pin plug on the dissipation board.

In the picture below is the proper wiring setup and color codes for each pin.

Note on communicating units: wires 3-7 will not be used. Only wires 1, 2 and 8 will be connected.

Dissipation error code table:

This information should help with wiring and checking your dissipation board and sensor. Depending on the equipment, wiring may differ depending on the options being installed. Check both installation and service manuals for the equipment you are working with to verify proper wiring and functionality of the dissipation safety system.

Should you have any questions, please feel free to reach out to your local Mingledorff’s for help.

Defrost in Cool Mode

Mon, 18 Aug 2025 14:02:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Defrost in Cool Mode

June 10, 2026

Beware of the defrost cycle in the cooling mode!

Sounds bizarre right? It is more common than you may think, in fact you may have already seen it without knowing so.

What does it look like?

The unit will be running in cool mode.
The outdoor fan will turn off.
The unit will continue to run the compressor IN COOL MODE
Yes, it will stay in cool mode the entire time, NOT heat mode.
If you check, the heat strips circuit (W) will have 24vac.
The compressor will run until it turns off on the high-pressure switch (if equipped)
The compressor will continue to repeatedly trip on high pressure (if equipped) until it runs hot and opens on internal overload.
After 10 minutes, the outdoor fan will come back on
When the compressor cools down, it will crank back up.

So, what causes this strange phenomenon? Please see the wire tracing below for reference.

On these units, the R (24vac) wire comes into the control board of the unit, it comes right back out of the control board to feed the outdoor coil defrost thermostat (DFT). These DFT thermostats contain contacts that should remain OPEN if the coil temperature is above ~65F. When the DFT closes its internal contacts, it returns R (24vac) to the control board to power the logic center.

Once the logic center has power, it starts monitoring the compressor run time. When the time has elapsed for the defrost timer (30, 60, 90 minutes), the defrost control board will initiate the defrost cycle. If the DFT fails in the closed position, then the defrost cycle will max out at 10 minutes and then continue back in the normal cool mode.

How do you troubleshoot this?

If you witness this or suspect this issue, all you need to do is:

1. remove the defrost thermostat (DFT) wires from the control board.

It is a white plug with two pink wires (see image below)
If the unit is actively in Defrost Mode, doing this will immediately terminate the defrost cycle.

2. use an ohm meter to ohm the two pink wires at the white plug.

ensure to make good connections to the wires.

3. If the coil is warmer than ~65F AND your meter shows resistance:

The DFT is bad.
Your meter should show OL (Open Line).
Replace the failed DFT.

This article is in reference to typical Carrier, Bryant, Payne, and WeatherMaker Heat Pumps.

Handling Refrigerant & Other Gases Safely

Mon, 18 Aug 2025 13:33:00 GMT

Anthony Coker

Technical Services Manager Southeast District

Handling Refrigerant & Other Gases Safely

June 10, 2026

Refrigerants and other gases used in the HVAC industry need to be respected and handled safely. The information given here is general in nature and not to be used as a substitution for the manufacturer’s instructions. This time we will cover safety around refrigerant and pressurized gases that are used in the HVAC industry. As a reminder, gloves and safety glasses need to be worn while working with these gases and refrigerants.

Refrigerants come in different containers, depending on the pressure rating of the refrigerant. Low-pressure refrigerants come in steel drums. Medium and high-pressure refrigerants come in returnable or disposable metal containers. Different refrigerants exert different pressure on the container depending on the temperature it is exposed to. For example, a refrigerant container exposed to cold temperatures will have a lower pressure inside the container, and will have higher pressure inside the container when exposed to hotter temperatures. So, never heat a refrigerant container with an open flame or any type of heater to raise the pressure in the container. If the container needs to be warmed up, place it in a conditioned area where temps are above where it was stored, or it can be warmed gradually and evenly with warm water not exceeding 125 degrees. The refrigerants in these containers are liquefied compressed gasses, and if missed handled or over heated, the container can burst, causing damage, injury, or death.

The liquid in the containers, when exposed to the skin, can cause frostbite or burns. Also, if released in a not so well-ventilated area do to equipment failure or miss handling of the refrigerants, could cause suffocation. Refrigerant vapor is heaver than air, invisible, with little to no odor, so equipment rooms with no ventilation or low places where equipment could be, may have areas where invisible gas is settling.

Make sure you read the labels on the refrigerant container as they will have safety and warning information about the product. You can also obtain technical bulletins and material safety data sheets from the manufacturers that would include information for your health and safety, also the flammability, and toxicity of the refrigerant.

Other pressurized gases in the HVAC industry are nitrogen, oxygen, acetylene, and LP. These gases are compressed and put in to medium to high pressure cylinders. Nitrogen and oxygen cylinders are pressurized at 2,000 psi. Acetylene, Liquid petroleum (LP), or butane are pressurized around 250 psi.

Oxygen should never be used to pressurize an HVAC system due to an explosion hazard with oil and oxygen. Oxygen can cause an ignition without a spark when it comes in contact with oil or grease. Do not handle oxygen cylinders or attachments with oily hands or gloves.

Acetylene and other flammable gases use regulators to adjust the pressure of the gas leaving the cylinders. Acetylene, which is used along with oxygen for welding in the HVAC industry, needs to be set at a pressure no higher than 15 psig, because over that it becomes unstable. Also, when using acetylene, never open the valve on the cylinder more than 1 ¼ of a turn, as this allows for a quick closing in an emergency.

When handling or moving, make sure any safety caps or carrying cases are used. If the valve were to break off the cylinder it would take off like a rocket. Be sure to follow all safety guides for storing all cylinders, and make sure they are in an upright position and secured. Do not store these cylinders with the different gases together. Due to the high pressures of nitrogen and oxygen, a regulator is used to adjust the pressure to a safe pressure while using.

LP gas is used a lot with furnaces for heating. Most HVAC techs do not deal with the LP tank, but may have to turn off the gas leaving the LP tank. The gas in the tank is a pressurized liquid that can cause frostbite or burns if it comes in contact with the skin. LP gas is heaver than air and will settle close to the floor or ground, and is highly explosive. Be very careful when going into an area where there is the smell of gas. Here are a few things that can be done for safety.

Clear the area of people and do not enter until safe.
Notify the local gas company.
Shut off the gas supply.
Do not use the light switches, if lights are on leave them on, if the lights are off leave them off.
Open windows and doors to ventilate the area.
Use a soap solution to look for a gas leak, never use a match or open flame.
Only use a battery-operated flashlight or approved safety light when searching for a gas leak.

Other dangers with Natural or LP gas used as a heating source occur when there is incomplete combustion of the gas due to improper installation or adjustment. This will produce aldehydes, soot, and carbon monoxide gas. Long term breathing of carbon monoxide can cause sickness or death.

The environment in which the HVAC persons work contains a lot of of hazards that need to be recognized and respected. Pay attention to the safety information on the product. Know and practice the steps needed to protect yourself and others in the case of an emergency. On the job safety is your responsibility. Keep yourself and others around you safe.

Understanding Active Dissipation

Thu, 10 Jul 2025 20:56:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

Understanding Active Dissipation

Along with new refrigerant for 2025, we’re also seeing new components for safety to be compatible with new Federal guidelines. Today, I will go over some of the new components, and the purpose they serve.

All products and systems designed for Puron Advance 454b, will require an active dissipation system to mitigate refrigerant leaks. The dissipation system includes a factory-installed leak sensor and a factory or field-installed dissipation control board (depending upon the equipment) that will override the thermostat when a leak is detected.

The leak sensor will trigger and activate a dissipation when it detects presence of refrigerant at a LFL ( Lower Flammability Limit) of 20%.

The dissipation board will shut off all ignition sources, any heating or cooling units that are operating, and will activate the blower to run so the air can be diluted for a minimum of 10 minutes or until the sensor reads <11% LFL.

There will be an additional 5-minute delay where the blower remains off to monitor for a leak. If the sensor doesn’t detect any refrigerant, the system will go back to normal operation.

The sensor and board should be mounted and wired into fan coils and small package units. No additional wiring is required. Please refer to the installation manual for proper mounting and wiring procedures.

June 10, 2026

Dissipation Control Board

Factory-Installed Leak Sensor

Understanding A Model Number

Thu, 10 Jul 2025 17:47:00 GMT

Anthony Coker

Technical Services Manager Southeast District

Understanding A Model Number

June 10, 2026

Why would you need to know what the letters and numbers in the model number represent? Can knowing the information from the model number help trouble shoot a problem with the unit? Commercial equipment model numbers are a little more detailed than residential. So, to show what information can be found from a model number, a light commercial rooftop unit will be used. The example model number will be M# 50FC-N16J2M6A3W3N0.

Unit Type , position 1 & 2 is marked by 50 in this example, so this unit is a cooling unit with the option to add electric heat.

Model Series , position 3 & 4, is marked by FC which is Standard Efficiency with the EcoBlue ECM motor.

(–) dash position 5, shows that the unit can have electric heat field installed.

Refrigerant Systems Options , position 6 is marked by N . which is a Two-Stage Cooling, Single Circuit with Humidi-MIZer system for dehumidification.

Cooling Tons position 7 & 8 is 16 which states this is a 15-ton unit.

Sensor Options position 9 is J which is Condensate Overflow Switch.

Indoor Fan Option position 10 is 2 which is Standard Medium Static Motor – Vane Axial EcoBlue.

Coil Options – RTPF (Outdoor – Indoor – Hail Guard) Position 11 is M which is (aluminum/ copper) Al/Cu – Al/Cu – Louvered Hail Guard to protect the outdoor coil.

Voltage , position 12 which is 6 , tells us that the unit needs 460 volts/3 phase/60 hertz power supply for it to operate.

Design Revision , position 13 is marked by a (-) dash in the installation or product data manuals. There is a letter that would go there based on the revision of the unit, the example model number that is being used has an A in the 13th position.

Base Unit Controls , position 14 is marked by 3 in this example which is SystemVu™ Controller.

Intake / Exhaust Options , position 15 is marked by W in this example which is Enthalpy Ultra Low Leak Economizer w/ Barometric Relief.

Service Options , position 16 is marked by 3 in this example which is Hinged Access Panels.

Electrical Options , Position 17 is marked by N in this example which is Phase Monitor/Protection.

Packaging Compliance , position 18 is marked by 0 in this example which is Standard.

Here is the break down of the model number from the manuals for the information above.

As you can see there is a lot of information in a model number. This information will inform you that the unit is gas heat with cooling, heat pump, cooling with or without electric heat, etc. With information from the model number, it could lead you in a direction to troubleshoot a problem. For example, the unit may not be removing humidity properly and the refrigerant pressures appear to be in range. Knowing the unit has a Humidi-MIZer system installed to aid in humidity removal, you can first focus on its operation to see if it is operating properly.

The model number is an aid in knowing what the unit is and the components that have been installed for the application the unit is designed for.

Sources:

Weather Maker® 50FC-*16 Installation Instructions

Product Data Weather Maker® Single Packaged Rooftop 48-50FC 8-16

TXV Ice Bath

Thu, 10 Jul 2025 17:35:00 GMT

Anthony Coker

Technical Services Manager Southwest District

TXV Ice Bath

June 10, 2026

Have you ever seen a stuck TXV?

Carrier typically uses hard shutoff valves on their equipment. A hard shutoff TXV means that when the unit turns off and the system pressures equalize, the TXV needle will fully close.

Where would you see stuck TXVs? / What are the key indicators?

When a unit has been sitting for an extended time, or if you install a brand-new valve: there is a chance that the needle could be stuck in the fully closed position. This will present itself as a restriction: low suction pressure AND high superheat.
If the valve is stuck wide open, the valve will have good superheat (typically between 5F-25F depending on load) while the unit has a high load [hot house] BUT when the house cools down, the superheat will fall under 5F.

So, if you have a stuck TXV, what can you do to assist this issue? Do a TXV Ice Bath.

After charge is confirmed/verified/ corrected (by subcool) and airflow is known to be good.

Allow the unit to run nonstop for a minimum of 10 minutes. Do not turn the system off at all for these tests.

Step One: Record the suction pipe temperature at the indoor unit.

Step Two: Remove the TXV bulb from the suction line, hold it in your hand and warm it by rubbing it with your thumb, do not use a lighter.

Step Three: After 2 minutes of holding the bulb in your hand, record the suction pipe temperature again.

Step Four: Take a cup of ice, add just enough water to cover the ice, then put the sensing bulb into the ice water.

Step five: After 2 minutes in the ice, record the suction pipe temperature again.

Step six: Remove the sensing bulb from the ice water, then reattach it to the suction pipe.

Step 7: After 2 minutes of being reapplied to the suction pipe, record the suction pipe again.

Note: if you feel the need, repeat the steps as many times as you like, but typically only one time is necessary.

When done, you should have written down or recorded 4 suction pipe temperature readings. Review the before and after results to determine if the valve is still stuck or if it is now functioning.

Normal operating TXVs should have a very noticeable temperature swing (typically 10F or more) on the suction pipe when changing from ice to hand or vice versa.

If you correct a TXV sticking one time, it is all good and should be free and clear of issues. However, if you catch it sticking again, it is recommended to schedule a replacement. A repeating issue of sticking TXV could eventually lead to a premature compressor failure.

45 MBCA Ductless Unit and the “CP” Error Code

Thu, 12 Jun 2025 16:48:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

45 MBCA Ductless Unit and the “CP” Error Code

June 10, 2026

Most ductless products have all of the error codes listed in the installation and service manuals. Error codes listed in the manual for a unit will give either a brief description of the code or sometimes a more in-depth meaning of the code with some potential resolutions. Knowing how to understand your error codes and come up with a resolution will help save time and get your unit back up and running.

The “CP” error code is a hard error code to find in the installation and service manuals. Many of your manuals don’t even list the “CP” error code. I personally could not find the “CP” error code in the manuals for the 45 MBCA unit I was working on, it was from previous experience by others to help resolve the “CP” error code.

The “CP” error code is related to the Remote ON-OFF on the indoor circuit board of the unit. The remote ON-OFF contacts are typically labeled CN23 on the board, which is a three terminal plug. As long as the contacts are closed between terminals one and three the unit will run. If the contacts become open between one and three the unit will no longer run. A controls company will sometimes utilize this set “on” contacts on the board to turn the unit ON and OFF.

Defrosting Thermostats: Learning & Understanding Heat Pumps

Thu, 12 Jun 2025 15:49:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Defrosting Thermostats: Learning & Understanding Heat Pumps

June 10, 2026

We have multiple articles about the defrost boards for residential and commercial units on our website and each has addressed different parts that you can read to help you diagnose what could be the problem with the system. Please follow the links at the bottom of this article to learn more about defrost boards.

The defrost thermostat closes because of the thermally actuated switch that is inside the defrost thermostat when the conditions have changed. In this case, the stub tube no longer is 32° ± 3°F. Since the heat pump has been switched to cooling mode by the defrost board – which allows the condenser coil to get hot – the board stops the fan whenever the heat pump goes into defrost mode. This helps the heat pump to get rid of the ice faster around the condenser coil and at the stub tube where the defrost thermostat is attached.

The defrost board has been program to follow a logic. In the case of our heat pumps, that process is to terminate the defrost mode because the defrost thermostat has reached the 65° ± 5°F needed to open the internal thermally actuated switch or the defrost board has run on defrost mode for ten minutes.

This information has come from a Bryant 215B heat pump service manual.

Other ways to check your defrost thermostat when you don’t have ice around it, is to run the heat pump on heat mode and carefully remove the black wire from the relay on top of the defrost board. This will stop the fan from running and the condenser coil should start frosting, making the temperature of the defrost thermostat 32° ± 3°F and checking the resistance until it closes reading 0.0 ohms indicating that is working properly. If not, it may be stuck open. Replace the thermostat. You can also remove the defrost thermostat from the heat pump and insert it into a cup with ice and water. Make sure the water its 32° ± 3°F, that way you know if it closes, the defrost works. If not, replace.

The other problem could be it’s stuck closed. You always need to know the temperature that surrounds the defrost thermostat. If it is attached to a pipe, you need to know the temperature of that pipe. Otherwise, you will be guessing. In the photo below, we have a temperature above 65° ± 5°F. We know the defrost thermostat should be open and on this defrost sensor it is open.

When you work on a heat pump system and you want to test defrost thermostats, there are several different test procedures to test the board and sensors. Most involve “forcing” a defrost by shorting out pins on the board which will advance the time on the defrost board allowing you to test if the board is reacting to the input from the defrost thermostat or not.

A defrost thermostat from a residential and small package product, or SPP, allows the low voltage to go from one side to the other, signaling the defrost board of 1 or 2 stage heat pumps that conditions, like the temperature, are about 32° ± 3°F. The 30, 60, 90 or 120 minutes interval depends on the model of the defrost board and how the factory or technician has set the timer. Once that time or defrost interval has elapsed, the logic of the defrost boards for Carrier, Bryant, Weathermaker, Payne and ICP heat pumps will switch the heat pump on the fly to “defrost mode” meaning the board energizes the reversing valve making the heat pump to switch to “cool” mode, the board then sends low voltage to the W2 white wire terminal signaling for the indoor unit, if equipped, to energize the heat strips. Also, the defrost board energizes the normally closed relay on the defrost board opening the electric circuit of the fan motor, thus stopping the condenser fan motor. The defrost thermostat is at the end of one of the feeder tubes and, on most units, is attached to a 3/8 copper stub tube on the bottom circuit of the condenser coil. If the heat pump has an aluminum coil, then the defrost thermostat will be made of aluminum (Do not mix a copper defrost thermostat with an aluminum coil or vice versa) See the photos below.

Now that we understand what the defrost thermostat does, let’s follow the service manual on what ways we can troubleshoot the board and defrost thermostat.

First, we know that on residential and small package products the defrost thermostat closes at 32° ± 3°F and opens at 65° ± 5°F so if you find one of our heat pumps running on heat mode but has a mass of ice or frost around the coil as well as at the defrost thermostat but it is still not going on defrost mode, then you need to determine what is causing this issue using your multimeter. Start by removing the small Molex connector with the two pink wires attached to the DFT from the defrost board and check what resistance or ohms you have between those two wires. OL or infinite means the thermostat still open. If that’s the case, replace the defrost thermostat which we know, at the temperature that surrounds the defrost thermostat, should be closed.

Second, we need to know if the defrost board works properly. With the same scenario, heat pump still running on heat mode, we need to test the board. With the Molex or pink wires removed from the DFT, you have two pins exposed. Attach an alligator jumper wire between the pins. Next, utilize a metal tool, like a flat screw driver, to short or connect the two speed up pins on the board. Make sure you count 5 to 7 seconds. It depends on the type of defrost board, but if you have the low voltage on the red wire from inside the unit, the logic will switch to defrost mode. When you hear the “swoosh” from the reversing valve, remove the screw driver from the speed up pins, otherwise will have a very short defrost. Once on defrost mode, you can confirm that the board is reacting to the defrost thermostat by removing the alligator jumper wire and the heat pump should switch to heat mode again.

An example below of one defrost board with the jumper on DFT terminals and with the screwdriver shorting the speed up pins. Wires were removed for clarity.

Please reference these articles below to learn more about defrost boards.

https://www.heatcool.com/technical-services/does-the-defrost-board-have-24vac/114474/

https://www.heatcool.com/technical-services/defrost-board-troubleshooting/139310/

https://www.heatcool.com/technical-services/where-does-the-orange-wire-go-on-a-heat-pump/74646/

https://www.heatcool.com/technical-services/schematic-reading-basics/114485/

Ductless Units and Compatibility Verification

Wed, 14 May 2025 17:02:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

Ductless Units and Compatibility Verification

June 10, 2026

Having all of the right components for your ductless system will lead to an easier install and customer satisfaction. Running back and forth trying to gather the right parts for your ductless system can be time consuming and could make your customer uneasy about the product. It’s a good practice to hold on to the install manuals that come with your ductless system to help clear up most of the install questions. If the manuals are lost or misplaced you can find the manuals for your product online at hvacpartners.com

There are several different types of ductless heating and cooling systems. These systems can be combined with various indoor and outdoor unit combinations. The indoor units can be controlled by a hand held remote, wired thermostat, or a 24v interface. Verifying all the right components of your ductless system before installation can save a lot of time and avoid confusion.

Find compatibility guidance in HVAC Partners under the "Technical Literature" header

You can get on HVAC PARTNERS online to verify indoor and outdoor unit compatibility as well as thermostat compatibility for your indoor units. When you pull up your unit on HVAC PARTNERS you can find the compatibility chart under documents in the technical literature tab. The chart will show you all of the thermostat compatibility for all of the high wall, cassette, ducted, console, and air handler style indoor units.

Use the compatibility charts to verify that your equipment will operate efficiently together.

Condensation From a High Efficiency Furnace

Wed, 14 May 2025 16:10:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Condensation From a High Efficiency Furnace

June 10, 2026

High efficiency furnaces, also known as 90% furnaces or condensing furnaces, use two heat exchangers to remove more heat from the combustion process than their mid-efficiency counterparts, which are known as 80% furnaces and only have one heat exchanger.

The photo on the left shows the wrong installation of the drain line from the condensate trap coming out of the furnace into the T from the evaporator PVC Pipe down to the condensate pump. There is no airgap inside the pump and that is not how the installation instructions are telling us to run the drain lines. The drawing on the right shows why it is not allowed.

Following the instructions on the manual for a 987MC High Efficiency furnace, two of the proper ways we can run or install the drains for a furnace like the photo above is to follow the drawings below.

Because of this, they generate flue gases much colder than those of a mid-efficiency 80% furnace. This doesn’t only change the way the furnace operates. It also changes the installation process as well.

In a high efficiency furnace, a great amount of condensation is involved. This water comes from two sources: the moisture that is already present in the air, and the combustion process itself, as the hydrogen atoms from the natural or propane gas molecules combine with oxygen to form water.

For the furnace to work properly, that condensation needs to be drained out or else it will accumulate inside the heat exchanger or inducer assembly. Most furnaces will have at least 2 internal drains, typically one for the heat exchanger and one for the vent, usually at the inducer outlet or on the inducer housing.

The secondary heat exchanger outlet is sealed inside a plastic part called the collector box, which is designed to collect the condensate and drain it out. All condensate drains go into a trap. The condensate trap is mandatory for a high efficiency gas furnace since the drain connects to the exhaust system of the furnace, leaving it open to the air. This would allow for a potential exhaust/flue gas leak in the living space and that’s why we need a condensate trap. Additionally, if there is no trap, the inducer motor would take air through the drain if it was left open, which could affect combustion and would prevent proper drainage.

One thing to think about when dealing with a condensate trap is potential blockage. The trap needs to be cleaned out regularly, and that should be done every maintenance. Rinse it out and make sure water flows through the trap properly from all its ports. If there is poor flow fill it up and blow through it to get out any obstructions.

The need for regular cleaning also means that drains should be installed in a way that allows the trap to be easily removed. Most furnaces come with additional parts like clamps and flexible hoses for installation. This makes it a little more accessible for the technician.

To ensure proper drainage, here are some helpful tips: make sure every component that produces condensate is sloped towards the drain. That means slope the vent down towards the furnace (typically a ¼’’ slope per foot of length, minimum) and slope the furnace itself! Look in your installation manual, most manufacturers will call for the furnace to be installed with a slight forward pitch to allow condensate to drain from the collector box. Slope the drain line and vent the drain after the trap to prevent airlock.

If you have any doubt that the installation or servicing methods that you are using are correct you should always refer to your installation manual, product data, submittals and your local codes.

All equipment is shipped with an installation guide specific to that equipment. Something to keep in mind is that different manufacturers may call for different installation procedures! Just another reason to ALWAYS follow the installation instructions.

High-Efficiency 90% furnace vs. Mid-Efficiency 80% furnace:

Evaporator Coil Corrosion: Why Do Some Corrode Faster Than Others?

Wed, 16 Apr 2025 15:42:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Evaporator Coil Corrosion: Why Do Some Corrode Faster Than Others?

June 10, 2026

Indoor coil corrosion followed by leak failure has been an issue in the HVAC industry for a long time. Although the occurrence rate of these failures is low nationwide, it seems that some locations see a higher failure rate than others.

A good example of this is a home with an air conditioning system that has multiple indoor coil corrosion-related failures while other homes around it with possibly the same system do not. Another example is multiple systems in a home or business where only some indoor coils are experiencing high rates of corrosion. Examples like these always leave us asking the question “ Why do some indoor coils corrode faster than others? ”

When you find evaporators like these on a customer’s home and its leaking, the next step is to replace it. However, we encourage you to search for the cause of the leak , especially when the homeowner explains to you that they had the system installed for a short period of time. Some homeowners might have more questions as to why this leak occurred, especially if they don’t use this system as often as the others. They may wonder why an evaporator coil is leaking with infrequent use.

Unfortunately, we tend to think that the evaporator coil is leaking due to a manufacturer error, but we must remember that each company has a different procedure of the manufacturing of their evaporators. So, if every company makes their coils differently, then why do you see the same issue with the different manufacturers?

What if I told you that the reason for the corrosion could be because of substances inside the house or space where the system is operating?

Although there are many potential causes of corrosion in evaporator coils, one we see most commonly is organic acids. There are many different types of organic acids, but the most common are formic and acetic acids. These acids can be found on different items in the house and there are several sources of both in and around the home.

Examples of formic acid sources : Building materials such as adhesives, cabinets, foam insulation, laminates, paint (both latex and oil-based) paneling and particle board. As well as household items like cosmetics, disinfectants, deodorizers, tobacco, wood smoke, and other vapors from electronic cigarettes.

Examples of acetic acid sources : Building materials such as vinyl acetate, cellulose fibers, plastics, paneling, particle board, plywood, silicone caulk, wallboard and wallpaper. It can also come from solvents such as vinegar and ones used in food processing.

As the examples above show, there is increasing evidence linking the cause of evaporator coil leak failures to agents present in household environments. Now, we shouldn’t tell someone the reason that their evaporator coil is corroding is because of the type of cabinets they elected to install in their home. The examples are just to show that there are substances like these acids that carry the risk of a high corrosion rate, and some can be higher than others. So next time you have a coil that is corroding and leading to leaks look at the overall application and ask yourself “ What in this environment could be leading to the corrosion on this evaporator coil? “

Here are some examples of coils with corrosion:

48GC Package Unit & System Sensor Smoke Detector D4120 Setup

Wed, 16 Apr 2025 14:39:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

48GC Package Unit & System Sensor Smoke Detector D4120 Setup

June 10, 2026

Smoke detectors can be used in many different residential and commercial applications. They can be utilized using the smoke shutdown or thermostat terminals on most of your package units and split systems. When smoke is detected the indoor fan will shut off by breaking your low voltage circuit through your smoke detector.

When wiring up a smoke detector on a package unit such as a 48GC, you will utilize your smoke shutdown terminals on the control board in the unit. Your field supplied 18/8 stranded two wire will run from your smoke shutdown terminals in your unit to the AUX A contacts on your smoke detector which is six and sixteen. Six is common and sixteen is normally closed.I

f your unit doesn’t have a set of smoke shutdown terminals on the control board to use you would then break “R” or “G” on the terminal strip or wire nut junction in the unit. Breaking “R” will kill power to your thermostat and stop all unit and fan operations. Breaking “G” will kill power to the indoor fan and stop indoor fan operation.

Remove the factory Jumper that is installed on your smoke shutdown terminals to hook up your two wire that goes to your smoke detector.
When breaking “R” one wire goes from “R” on the terminal strip to “C” on the smoke detector, your second wire goes from “NC” on the smoke detector back to your red wire in your unit that goes down to “R” on the thermostat.
When breaking “G” one wire will wire nut with “G” your green wire in the unit going to the thermostat and then to “C” on the smoke detector, your second wire will land on “NC” on the smoke detector and land back on “G” on the terminal strip in the unit.

Vacuum Pump Performance

Tue, 11 Mar 2025 20:26:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Vacuum Pump Performance

June 10, 2026

Most technicians are aware of the importance of changing the oil in your vacuum pump regularly. However, if you aren’t, this article will explore and explain the consequences of neglecting that service.

On severely contaminated vacuum pumps, one of the easiest ways to spot if your pump needs a good cleaning is to look at the sight glass. If the oil looks milky, rusty, or full of debris, then the inside of the pump is in worse shape.

If your pump is not damaged or it has been a while since you changed the oil in it, there is still hope that you can restore the pump to its original operating efficiency.

One of the most common methods is known as “flushing.” This process is outlined below

Step 1 : Always drain pump before flushing. If the oil is badly contaminated, you may need to do this multiple times.

Step 2 : Slowly pour 1/3 to 1/2 cup of Vacuum pump oil into the intake connection while the pump is running. The oil will quickly pass through the pumping chamber washing out contaminants.

Step 3 : Repeat as required until contamination is removed from oil reservoir, pump rotors, vanes and housing.

Step 4 : When the pump has finished draining, close drain valve on pump and fill to the oil level line. Remember to dispose of the oil properly.

As you can see, the advantage of this extended flushing technique is that all the internal parts of the module are cleansed of contaminants.

When adding oil to the vacuum, do it slowly until level rises to the oil level indicator. Most manufacturers have an indicator.

If the oil level is too low, you will hear air coming out of the exhaust. If the oil level is too high, excess oil will be blown out of the exhaust.

Below, you can find valuable pump information from a manufacturer.

“Vacuum pump oil is one of the most rigorously used oils, and it’s used in a tough environment,” Vacuum pumps are designed to remove moisture, air, as well as contaminants from the system. The accumulation of contaminants in the vacuum pump oil is normal. Because of this, it’s important to change the vacuum pump oil after each use.”

“The pump oil is like the life blood of the vacuum pump.” In addition to providing all the lubrication and sealing of the pumping components, it also collects all the moisture and contamination of the system. Check oil level through oil sight glass before each use. The main cause of vacuum pump failure is low oil levels and contaminated oil.”

“Because the vacuum pump oil holds the contaminants in suspension, they float around in the vacuum pump system. If you don’t remove them, they can significantly shorten the life of your vacuum pump, which is why you should change the oil every time, having to replace a vacuum pump can be a hefty expense – changing oil is a lot less expensive.”

“For best results, it is recommended that the pump runs for at least 15 minutes before changing the oil. “The reason for that is to get the moisture and contaminants floating around and suspended, rather than leave them laying at the bottom of the tank.

It is imperative to use good quality vacuum pump oil. You may be wondering where you can find vacuum pump oil? At any Mingledorff’s store! Ask any of the inside sales team members at the counter. We offer the top brands, including Uniweld, YellowJacket, Fieldpiece, JB Industries and Nu-Calgon.

The Mingledorff’s Technical Service Department also performs vacuum pump clinics at stores when they have Open House events and some Spring and Fall Service Update classes. Please stop by and let them change the oil in your vacuum pump for FREE!

Toshiba/Carrier U-Series Installation and Troubleshooting: L11 and E17 Error Codes

Mon, 10 Mar 2025 20:56:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

Toshiba/Carrier U-Series Installation and Troubleshooting: L11 and E17 Error Codes

June 10, 2026

Installation of a heat recovery VRF system allows multi-zone heating and cooling. A heat recovery system allows you to heat and cool at the same time. One room can be heating and another room can be cooling allowing comfort for all occupants in the building.

Proper Installation is critical with VRF systems. Paying close attention to your wiring, dip switch settings, and code settings and thermostat programming is very important. Having a clear understanding of wiring diagrams and initial installation procedures is a must.

It is a good practice to make sure all of your dip switches are set to the factory position on all of your flow selector boxes during installation. If the dip switches are not set in the factory position you will have L11 and E17 error codes to follow. You can verify the factory dip switch settings by looking at access door on the flow selector box. The L11 and E17 error codes can also be caused by wiring issues, good wiring practices can prevent having problems.

Changing dip switches on your flow selectors is not necessary because all of your flow selector addresses and port numbers are set using and codes 00FE and 0105 on your thermostat. Making sure your flow selector address and your flow selector port address is correct will make the start up process much easier. If care is taken and you have a good understanding of the wiring and installation of a VRF system the start up process can be close to seamless.

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Ductless Systems: Solid vs Stranded Wire

Wed, 19 Feb 2025 15:58:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

Ductless Systems: Solid vs Stranded Wire

June 10, 2026

There are many different options and advantages to using a ductless mini-split system. From new construction installation to a retrofit application, these systems can be a solution for your heating and air-conditioning needs. There is no duct work needed for these systems allowing them to be installed almost anywhere without any major installation issues.

When installing these systems, it is highly recommended to run 14/3 stranded wire. Running stranded wire can prevent wire breakage and communication issues. Solid wire can break if installed incorrectly and cause communication and power issues with your system. Stranded wire is a lot more flexible and pliable with several soft strands of copper wire versus one hard copper wire.

Troubleshooting solid copper wire can be tricky. A solid copper wire that is partially broken can still read continuity when checking it with a volt meter. A lot of time, effort, and energy can be spent on a job troubleshooting power and communication issues due to the installation of solid wire. Making it a rule to run stranded copper wire on all ductless systems can save a lot of time and aggravation.

Most of the 14/3 AWG stranded copper wire can be purchased at Mingledorff’s and several other HVAC suppliers.

38MARB

Outdoor Unit Single Zone Ductless System

Sizes 06 to 36

Power and Communication Wiring: The main power is supplied to the outdoor unit. The field supplied 14/3 power/communication wiring, from the outdoor unit to the indoor unit, consists of four (4) wires and provides the power for the indoor unit. Two wires are high voltage AC power, one is communication wiring and the other is a ground wire.

CABLE SIZE REMARKS

Connection Cable 14AWG 3 wire + Ground 1Φ 208/230 V

(Stranded wire is recommended)

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Tech Mate Pro: Fast, Accurate ECM Testing

Wed, 19 Feb 2025 15:28:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Tech Mate Pro: Fast, Accurate ECM Testing

June 10, 2026

Working on any system that has an Electronically Commutated Motor (ECM) is always a challenge.

This type of motor receives an input voltage or communication signal to determine the operating speed . But, how do you test such a motor? Mingledorff’s has two tools that provide guess free, stress free, and accurate diagnosis in a fraction of the time you’d spend using a voltmeter and troubleshooting chart.

Other ECM testers are designed to isolate the blower motor and help the technician determine if the blower motor is defective, like the Tech Mate Pro KFASD0301VSP. The ECM tester can only be used to test the variable speed ECM 2.0 and 2.3 blower motors on thermostatically controlled systems. This includes residential fan coils , small packaged products, some models of 80% furnaces and 90% condensing furnaces. This tester should not be used on 2.5 motors.

The ECM Tester contains alligator clips to connect to the 24Vac from the circuit board of the unit being tested.

Note: This tester will rotate the motor a portion of the expected airflow. This is not intended to replace the functionality of the board.

Shut off power to unit.
Unplug the 16-pin connector for ECM 2.0 and 2.3 motors or the 4-pin connector for ECM 3.0 motors. Leave the 5-pin high voltage plug connected to the ECM blower motor. Plug the 16-pin connector for ECM 2.0 and 2.3 motors or the 4-pin connector for ECM 3.0 motors from the ECM Tester shown in Figure 1. to the ECM motor.
Attach the blue lead of the tester to the R terminal on the unit control board and the black wire to the C terminal on the unit control board. The ECM 3.0 may require the use of additional alligator clips or piggy-back connectors.
Turn on power to the unit. The green POWER LED found in the switch should light up.
The green motor LED is attached to the output pins of the motor. The LED will blink dimly when the motor power is turned on. As the revolutions per minute of the motor increase, the brightness of the LED will increase.

The KGBSD0301FMS for variable speed motors found on some furnaces.

Figure 1: Tech Mate Pro KFASD0301VSP

Testing the motor with the Tech Mate Pro:

Understanding Furnace Fault Codes 13 and 31

Fri, 17 Jan 2025 21:24:00 GMT

Anthony Coker

Technical Services Manager North Georgia

Understanding Furnace Fault Codes 13 and 31

June 10, 2026

With the implementation of near-field communication boards (NFC) installed in certain products offered by Mingledorff’s, the use of apps is extremely important to use in the field.

Mingledorff’s Technical Service Team recommends that you download the app(s) that is most convenient for you according to the brand of your mobile device or tablet.

By pointing your device’s camera at the QR code you choose, your device will give you the option to open the app store to download your app and thus be able to communicate and interact with that component or system. The use of smart devices with wireless or NFC helps the service technician become more effective in the field diagnosing service-related issues.

The service technician in the field will come across a furnace with a diode light on the board indicating a specific fault code that the furnace is having a service-related issue. It can often be overwhelming to the service technician, since the speed and duration with which the light is blinking to indicate the fault code is especially important and, in some situations, it is not easily understood what the fault code represents.

To resolve any problem, we first must know what the problem is and once we understand it, we can take the necessary actions to resolve the issue. Please review the video of an NFC furnace board with a code that you often have trouble understanding.

As you watch the video, the NFC board is flashing the LED code with three short flashes followed by one long flash. As a reminder, each status code is a two-digit number with the first digit determined by the number of short flashes and the second digit by the number of long flashes. The service technician can now review the service label available in your installation manual or on the decal attached to the furnace. The manufacturer recommends how important and necessary that the service technician always follows and understands the instructions described in the service instructions on how to follow the troubleshooting sequence and the steps on how the flashing LED represents a fault that the furnace is having.

The first digit of the error code is indicated by short blinks outlined in yellow. In practice as we reviewed the video are the times that the light is on for a noticeably brief period in such a way that when it flashes at a fast speed or seen in another way a noticeably brief time would be our first digit. The first digit is simply one, two, three extremely fast.

The second digit of the codes is indicated by the long blinks, In the video the service technician can see how the LED takes a little longer compared to the first digit. So, when the light is emitted for a longer period, it is the indication of the second digit.

By viewing the next video, we will be able to indicate what the code is?

Manual in Spanish

Manual in English

Remember, just as we did with code 31, to understand code 13, it is necessary that the service technician use the same procedures to determine the code 13. The first code is the one that is the fastest, then it is determined that it is one, since it is the fastest, and the second digit is three, since the duration of the light is longer.

It is especially important that the service technician understands the codes that the NFC or other control boards are indicating so that the issue for the homeowner isn’t mis-diagnosed. If the flashing sequence is not followed correctly, as the videos are shown that the code 13 or quite different as for the code 31. Code 13 indicates a possible limit issue where the code 31 indicates a possible pressure switch issue. With the correct code is obtained the service technician can focus on the prompt and correct solution for the customer.

When the service technician comes across other fault codes on a control board with LED indicator lights or you are in any other situation, simply find or download the product/service manual on your device using one of our APP’s. Review the instructions as we did here, and you will find that the troubleshooting process will become simpler to resolve the customer’s issue.

If you have any questions or comments, please do not hesitate to let us know on any of the phones, as well as in the email, If you want to print the item just select the printer icon or if you want to send it to someone else press the envelope icon to send the link using your email.

How to Measure the Voltage on Triac Output

Fri, 17 Jan 2025 20:21:00 GMT

Anthony Coker

Technical Service & Support Manager

How to Measure the Voltage on Triac Output

June 10, 2026

A triac is an electronic switch, very much like a transistor. Triacs are commonly used in light dimmers, motor speed controls computerized control circuits.

Triacs are used on all Carrier and Bryant model thermostats, FE fan coil boards, furnace boards, NIM’s, zone board damper actuator outputs, etc., just to name a few. Plus, many other manufacturers use Triacs.

Triacs are often used because they require less space on a circuit board than a relay. If you don’t see a relay on the board, the output is most likely driven by a Triac.

Pros:

Better than a transistor as it has much better current surge rating – it can handle more current as it simply turns on more.
Inexpensive compared to relays.
Eliminates mechanical wear in a relay

Cons:

Can’t manually control turn-off with the gate; must turn off by stopping current through the device via the terminals.

A triac is essentially an electronic switch. There is a difference, though, in that a triac is not a dry contact and it leaks a very small amount of current when it is “off”.

If you were to check the voltage across a triac with a voltmeter when there is no load connected to the output, you will read a voltage. If a load is connected and the triac is “off”, the voltage reading across the outputs will be 0.

This can be very confusing for someone not familiar with triacs. It is possible to see a voltage when the triac is not actually being signaled to turn on.

A voltmeter has a very high resistance circuit in it. This is so that only a very small current to flow through it so voltage can be measured.

A solenoid, relay, contactor, etc. does not have a high resistance and allows current to flow voltmeter. (remember V=IR)

When a triac is connected to one of these loads the voltage across it then is shown to be zero when the triac is turned “off”.

A load must be connected to the triac output before measuring the voltage. A simple test, if you don’t have a voltmeter, would be to connect a relay to the output. If the relay energizes, you know the triac is “on”, and if not, the triac is “off”.

Triac output with no load connected, triac not energized

What is a Triac?

A TRIAC (TRIode for Alternating Current) is a 3-terminal AC semiconductor switch.

Composed of 2 thyristors facing opposite directions such that it can conduct current in either direction.

MT1 and MT2 are current carrying terminals while the Gate terminal is used for triggering by applying a small voltage signal.

Once triggered, it continues to conduct current until the current falls below a threshold value.

Pros and Cons

How do you measure the voltage?

Triac output with load connected, triac energized

Relays and Relay Capabilities (RIBU1C & RIBU2C)

Wed, 15 Jan 2025 21:43:00 GMT

Anthony Coker

VRF Tech Support & Equipment Verification Southwest District

Relays and Relay Capabilities (RIBU1C & RIBU2C)

June 10, 2026

There are many capabilities and functions of RIB relays. The RIBU1C and the RIBU2C are two of the most common and user-friendly relays. Using 10-30 AC/DC voltage or 120V AC voltage, these relays can control one or two legs of power. They are commonly used to break 120V and 208/230V high-voltage power sources. These relays have normally closed (N/C) and normally open (N/O) contacts that change state when voltage is applied or removed.

Power is applied to the N/C set of contacts on the RIBU1C through the yellow and blue wires, with yellow serving as common and blue as N/C. The N/O set of contacts is controlled by the yellow and orange wires, with yellow as common and orange as N/O. If you have a RIBU2C, it contains two relays instead of one. The wire colors for the N/C and N/O sets of contacts for the first relay are the same as those of the RIBU1C, but they differ for the second relay. For relay two, the N/C set of contacts is controlled by the purple and gray wires, with purple as common and gray as N/C. The N/O set of contacts for relay two is controlled by the purple and brown wires, with purple as common and brown as N/O.

These relays are a simple solution for interlocking external pieces of equipment with various HVAC systems, such as interlocking a rooftop unit with a 120V exhaust fan. When the indoor fan on the rooftop unit is energized, the contacts on the RIB relay close, activating the exhaust fan. By utilizing C and R on the rooftop control board with the Wht/Yell and Wht/Blu wires on the RIB relay, along with the yellow and orange wires to break 120V for the exhaust fan using the N/O contacts, this process can be achieved effectively.

These relays are suitable for both commercial and residential applications. They are widely available at most major HVAC suppliers and are quick and easy to install.

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Finding Manuals Without an Account

Tue, 17 Dec 2024 21:09:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Finding Manuals Without an Account

Carrier/ Bryant/Heil has a website that houses all their manuals. This includes install, product data, product submittal, service manuals, accessory kit, and many more!

This website is hvacpartners.com , although an account is free, sometimes you may lose your login credentials.

When you need a manual, you need it right then. You typically do not have time to reset passwords, or hunt down an email address.

Here are a few solutions to get around not having your login credentials.

*Sometimes specific service manuals may be reserved for logged in person*

Access without logging in on the following brand specific sites:

Carrier.hvacpartners.com

Bryant.hvacpartners.com

Heil.hvacpartners.com

If you are not able to access these websites above, then you can download the needed app from the selection below, then select “Continue As Guest”:

June 10, 2026

Get out there and put this to good use!

Carrier only:

Carrier Service Technician

Bryant only:

Bryant Service Technician

Carrier and Bryant:

RC Mobile Technician

Heil:

Fast OEM Mobile Tech

Hall Effect Switch Troubleshooting and Helpful IGC Codes

Tue, 17 Dec 2024 19:32:00 GMT

Anthony Coker

Technical Service Manager

Hall Effect Switch Troubleshooting and Helpful IGC Codes

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

With the heating season coming up, I wanted to share a common issue and how to troubleshoot the Hall Effect switch. I’ve also included a chart with codes, what they mean, and what to look for when troubleshooting a furnace.

Troubleshooting the Hall Effect Switch

Tools needed:

Voltmeter capable of measuring DC volts

With the three-wire plug unplugged:

With power applied to the unit, unplug the three-wire plug and measure the pins as follows:

1. Connect the negative or black lead of the meter to pin three on the circuit board.

2. Connect the positive or red lead of the meter to pin one.

3. The meter should read between 7.5 and 10 volts DC.

4. Move the red or positive lead to pin two. It should read between 21 and 24 volts DC.

5. Replace the circuit board if these pins are outside these readings.

With the three-wire plug plugged in:

With power applied to the unit and the three-wire plug in place, measure the pins as follows:

1. Connect the negative or black lead of the voltmeter to pin three on the circuit board.

2. Connect the positive or red lead of the voltmeter to pin one.

3. Slowly rotate the induced draft motor. On half of one rotation of the induced draft motor shaft the voltage reading should be less than 1 volt DC. On the other half of one rotation the voltage reading should be between 6.5 and 9 volts DC.

4. If the voltage reading is not less than 1 volt DC on half of the rotation of the motor shaft and not between 6.5 volts and 9 volts DC of the other half of the shaft rotation, replace the Hall Effect Switch.

5. Move the red or positive lead to pin two. It should read between 16.5 and 21 volts. If not, replace the Hall Effect Switch.

IGC Codes

VRF Login / Brand Selection (Carrier or Bryant)

Tue, 17 Dec 2024 19:11:00 GMT

Anthony Coker

VRF Tech Support and Quality Assurance • North Georgia, North Alabama

VRF Login / Brand Selection (Carrier or Bryant)

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Once your Carrier or Bryant VRF system is up and running, there’s one final step to complete if you’re using a Central Controller (sometimes referred to as a Touchscreen). The Central Controller offers various features beneficial to both contractors and end users, including scheduling, adjusting and locking temperature settings, reading error codes, and making minor adjustments.

Let’s walk through the installation process to get started.

As you turn power you will see this screen. Asking to select language.

Select “Carrier” or “Bryant” “No logo” and click “Save”.

One of the following screens will be displayed depending on the user selection:

Auto Search — The Touch Screen Central Controller can automatically search and connect to the system’s connected units. Devices connected to the controller are automatically searched and brought into the Central Controller / touchscreen.

1. In the main menu, click the [Install] menu icon. You see the word install. Press INSTALL

2. Click the [Auto Topology] button. Then it will start to search for all the units that you have. When it has found all your units you then will hit save.

Make sure you tap “SAVE”

3. If everything is successful, the home screen should look like this and have all equipment items including Indoor and Outdoor units.

4. You will need to hit INSTALL.

You will then see this screen.

5. Tap the name of the unit to update to what you’d like. For example, “Lobby, room number, etc.” Naming a unit by its physical location allows the end user to communicate an issue easier and control certain areas like meeting room when not in use.

You will hit the save button and it will be saved.

Furnace Code 12

Wed, 20 Nov 2024 14:30:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Furnace Code 12

Also known as code 121 on 2023+ furnaces

June 10, 2026

Since the code 12 is only initiated when the logic sees 24vac on W at the same time power is applied to furnace logic, this will allow you to bypass the 90-second delays that slow you down.

When you are servicing a furnace whether it is for seasoning cleaning or diagnosing a no heat, sometimes the furnace will stay off due to a “time delay” Code 12. Although this off time is only 90 seconds, it feels like an eternity!

What is Code 12, and how do we prevent it?

Every modern furnace control board has Logic built into them; this means they are capable of processing inputs to decide the needed output. These logic centers need 24vac to power up. If the board voltage drops below 19vac OR if the voltage is gone (zero), then upon the voltage rising above 19vac, the logic center will reboot.

When the logic center reboots (while the furnace has a 24vac call on W) it does not know if the burners were burning prior to the voltage drop. So, to be safe, the logic will run the blower only for 90 seconds instead of firing the burners and entering the blower off delay (as a normal call for heat would do). THIS is what a code 12 is (blower on after powering up). Without this safety, in the event a blower delay was initiated while the heat exchanger was already hot, then the chances of burning a hole in the heat exchanger would be high.

Code 12 prevention:

***This should only be done if you know (for a fact) that the heat exchanger is not hot***

When you power down the furnace during troubleshooting, remove the wire off the W terminal, apply power back to the furnace, THEN put the W wire back on the furnace board terminal. This will make the logic see 24vac on W AFTER the power turns on.

New Furnaces

Tue, 19 Nov 2024 21:28:00 GMT

Anthony Coker

Technical Service Manager

New Furnaces

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Review the following video for information on new furnaces including troubleshooting, app integration, and more!

Changing Celsius to Fahrenheit on Mini-Split

Tue, 19 Nov 2024 21:16:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Changing Celsius to Fahrenheit on Mini-Split

Have you ever installed a mini-split and after commissioning, the wall control is showing the temperature in Celsius instead of Fahrenheit?

June 10, 2026

To change Celsius (C) on the thermostat to Fahrenheit (F) you must do the following.

1) Push the up & down buttons simultaneously on the wall control. If it doesn’t work, push up & down together on the remote while pointed at wall control.

2) If first step doesn’t work, point the remote at the indoor display and press the up & down arrow at the same time.

3) If the second step doesn’t work, remove the wall control from the wall and unplug it. Then, press the up & down buttons simultaneously on remote while pointing at indoor display. Plug the wall control back in and it will change C to F.

In short, following the steps listed above will allow the temperature reading to switch between C and F. This is not listed in the owners manual. The owners manual is where you will normally find the advanced menu settings. (Not the Install Manual) 70 degrees F = 21 degrees C if you find that you are still having issues and need to set a temperature for your customer.

Updating Your SMAN/Testo Gauges

Thu, 17 Oct 2024 15:04:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Updating Your SMAN/Testo Gauges

Some of you might have an older SMAN/Testo digital gauge. With the new refrigerants coming, you might need to update your SMAN gauges (digital HVAC manifold gauges) for several reasons:

1. Software Updates:

Manufacturers release firmware updates that can improve accuracy, fix bugs, add new refrigerants, and improve overall performance.

2. New Refrigerant Compatibility:

Updates often include support for newly approved refrigerants. This is crucial to ensure your gauges can measure all the refrigerants you may encounter.

3. Improved Functionality:

Updates can include better features like faster readings, improved Bluetooth connectivity, or enhanced diagnostic tools.

4. Bug Fixes:

Like any electronic device, there may be minor issues or glitches in the original software that need fixing.

5. Extended Battery Life:

Some updates can optimize power usage, improving battery efficiency.

Updating ensures your gauges remain accurate and compatible with the latest industry standards, providing you with the best performance.

To update a Fieldpiece SMAN gauge, you can follow these steps:

Download the latest firmware: Go to the Fieldpiece website and navigate to the Support page, then the Software & Firmware Updates page.
Prepare the SMAN: Turn off the SMAN and disconnect the micro-USB cable.
Hold down buttons: Press and hold the wireless on/off button, the zero weight button, and the power button until dashes appear in the middle column of the screen.
Connect the SMAN to a computer: Use a micro-USB cable to connect the SMAN to a computer. The cable must be able to transfer data.
Start the software: Double-click the downloaded file and follow the instructions.
**Click **: Send**** After the SMAN is connected to the computer, a window will appear and prompt you to click Send.
Wait for the update: The update process may take a few minutes. When the process is complete, the screen on the updater will change automatically.

June 10, 2026

You can check your SMAN’s current firmware version by turning it off, pressing and holding the blue power button for about six seconds, and looking at the top right corner of the display.

Here are some steps to update the refrigerants on a Testo digital gauge:

Use the Testo refrigeration app or the Testo Smart Probe app to select the menu refrigerant list
Select or deselect refrigerants from the list
Do not cancel the connection to the manifold while the transmission is in progress
The transmission status will be displayed on the screen
Once the transmission is complete, the selected refrigerant can be chosen in the instrument

How to Read a Ladder Diagram

Thu, 17 Oct 2024 14:46:00 GMT

Anthony Coker

Technical Service Manager

How to Read a Ladder Diagram

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Ladder diagrams, also known as ladder logic, are a type of electrical notation that illustrates how relays and electromechanical switches are connected.

Understanding Rungs and Rails

Read from left to right, top to bottom

The power flows from left to right across each rung, and the diagram is read from top to bottom.

Identify the rails and rungs

The vertical lines are called rails, and the horizontal lines are called rungs. The left rail is usually the power source, and the right rail is the ground or neutral connection.

Understand the rungs

Each rung represents a single operation or condition in the control process. The logic symbols on the rung, along with the state of the inputs, determine the output state.

Analyze the input devices

Input devices can be connected in parallel or series. In a series connection, all devices must be activated, while in a parallel connection, only one device needs to be activated.

Look for numbers and letters

Wires in control systems are often marked with numbers and/or letters for identification. All points that are electrically common must have the same label.

Use a cross-reference system

The rungs are usually numbered on the left side of the rail, and the right side of the rail references the contacts associated with the coil.

In a ladder logic diagram, the vertical lines on either side are called rails, while the horizontal lines connecting the rails are called rungs. The left rail is typically associated with the power source, while the right rail represents the ground or neutral connection. The rungs contain the ladder logic symbols that define the system’s control logic. Each rung represents a single operation or condition in the control process. The logic flows from left to right, with the output state determined by the state of the inputs and the logic symbols on the rung.

Interpreting Symbol Arrangements

The arrangement of ladder logic symbols on a rung determines the function and behavior of that rung within the control system. One typical arrangement is the series connection of NO contacts. In this configuration, all the contacts must be closed (i.e., their associated conditions must be true) to energize the output coil. This arrangement represents a logical AND operation, as all the input conditions must be met for the output to be activated.

Another typical arrangement is the parallel connection of NO contacts. In this configuration, the output coil will be energized if any contacts are closed (i.e., their associated conditions are true). This arrangement represents a logical OR operation, as any of the input conditions being met will activate the output. In more complex ladder logic diagrams, combinations of series and parallel connections can be used to create intricate control logic.

Carrier VRF Static Pressure

Thu, 17 Oct 2024 14:26:00 GMT

Anthony Coker

VRF Tech Support and Quality Assurance • North Georgia, North Alabama

Carrier VRF Static Pressure

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

All ducted VRF systems come from the factory set for 0” of static pressure. As we know from experience, this is not possible when any ductwork is attached. 0” of static pressure is only in a factory setting with nothing attached.

You may be asking yourself “What happens if Static isn’t updated?” When static pressure isn’t set on a ducted indoor unit, this makes the algorithm always operate the fan in the lowest fan speed possible. As you can imagine, this won’t work. So how do we set Static Pressure? This can be achieved on both WIRED remote controls. The programmable controller is not only an easy-to-use thermostat, but also a great service tool as well.

Let’s start with the programmable control first:

40VM900003 programmable (Carrier)

40VM900013 programmable (Bryant)

We need to get into the Service Menu by Holding “FAN” and “BACK” for roughly 3-5 seconds.

Once inside the service menu scroll down to Page 2 of 3 indicated by the top right corner of the screen. Highlight “Static Pressure” and hit “Menu/Ok”.

In the menu use the Up/Down arrows to choose static pressure setting and press Menu/OK to confirm.

Now on to the non-programmable model.

40VM900002 non – programmable (Carrier)

40VM900012 non – programmable (Bryant)

This model uses a different method to make any advanced settings. First, press any button to wake the controller up and light the screen then press and HOLD “MODE” and “FAN” for 5 seconds to access the Service Menu. You’ll know you’re successful when the display changes to 0 0.

The code on the left is known as “1G” and the right as “2G”. Pressing the up and down arrow scrolls through the various 1G codes. Static Pressure is #10 for 1G. Press “OK” to move to the 2nd code. Use the chart below to determine what 2G code should be used then press ok to confirm.

To exit back to home screen either wait 30 seconds or press back twice. This applies to both controllers.

Now that static pressure is set in the thermostats you should hear the fans ramp to their appropriate speeds.

If you are ever in doubt about which thermostat you are working with, below is a side-by-side picture to help you figure it out.

Ductless Commission/Testing In Heat Mode

Tue, 17 Sep 2024 14:01:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Ductless Commission/Testing In Heat Mode

Have you ever installed a mini split in the summertime? During the commission the AC would work well, but in heat mode unit will not run at all. To know the reason why the unit will not run in heat mode, we must know what each T’s sensor does.

T1: Indoor room temperature
T2: Coil temperature of indoor heat exchanger middle
T2B: Coil temperature of indoor heat exchanger outlet
T3: Coil temperature of condenser
T4: Outdoor ambient temperature
T5: Compressor discharge temperature
Td: Target temperature
Ts: Set Point Temperature

In this situation, we know the unit works well in cool mode. In heat mode, the unit will not run at all. In heating operating range, the unit will not heat if the outdoor temperature exceed 86 degree.

The day the tech tried to commission this unit. The outdoor temperature was over 90 degrees. The unit was on a black roof and in direct sunlight.

June 10, 2026

The Sleeping Carrier/Bryant VRF

Tue, 17 Sep 2024 13:27:00 GMT

Anthony Coker

VRF Tech Support and Quality Assurance • North Georgia, North Alabama

The Sleeping Carrier/Bryant VRF

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This month we will be covering a scenario that baffled even the Mingledorff’s VRF group for a while. Hard to believe right?

Scenario: You arrive at a jobsite with a Carrier VRF unit not cooling. Looking at all the components of the system, there aren’t any errors. Maybe something is going on with the Outdoor Unit (ODU). Looking at the spot check and main boards and they both display a _0_0.

Only if it is the filter board for the #1 compressor the unit will have a blank display.

Remembering what you learned in class, this is telling you the compressors are both at 0 RPS or OFF. Time to get out the computer with STT. First thing you notice is the ODU grayed out like it’s in standby mode. “That’s weird, I know all the thermostats are set to 70 and it’s 76 degrees in the space.”

Given this very ODD scenario we need to know a little information beforehand. Every compressor and fan motor have their own inverter boards. The location of the inverter boards depends on the quantity of compressors.

Compressor 1: Left side of ODU in the main control panel behind the main board.

Compressor 2: Right side of ODU in the panel shown below.

Compressor 3: Will be the panel that is the furthest right side of the unit.

Today we will be focusing on the 2nd compressor inverter board. After removing the access panel for Compressor 2 you will see the Fuse/AC filter board. The compressor board lies behind the hinged door. LEDs can be accessed by the viewing window on the top right.

RED LED: Power to board

GREEN LED: Status/Error

If there is an error on the green LED for the Compressor 2 Inverter board use the chart below to give you an idea where to start:

The error more than likely will be an L0 or L7 code indicating either a bad inverter board for the compressor OR fuse board.

So where do we start? The easiest and fastest thing to check is the fuses. We need to ensure these non-replaceable fuses are intact. This can be accomplished 1 of 2 ways.

Power on: Check VAC voltage on either side of the fuse. If you get a voltage reading the fuse is bad. If the fuse is good, you should get a 0 VAC reading.

Power Off: Wait at least 3-5 minutes for capacitors to discharge and check continuity across the fuse.

!!WARNING!!

WHEN WORKING ON LIVE EQUIPMENT FOLLOW ALL SAFETY MEASURES. MINGLEDORFF’S IS NOT RESPONSIBLE FOR INJURY OR DAMAGE.

If any of the fuses are blown the board needs replaced. Contact your TM to order.

If you have any questions please feel free to contact the Mingledorff’s Technical Service Team.

Troubleshooting PWM Furnace Motors

Mon, 16 Sep 2024 20:35:00 GMT

Anthony Coker

Technical Service Manager

Troubleshooting PWM Furnace Motors

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

The blower motor has a 115 VAC applied to it anytime the furnace is powered. First manually close the blower door switch then verify the 115 VAC power is between L1 and Neutral (L2) Wires.(L1 and Neutral (L2) are removed for clarity in this photo!

15 VDC is nominal
May be slightly higher or lower. Actual line voltage affects low voltage.
Meter type affects reading.
If reading is unstable or scrolling
Check harness connectors and pins Clean meter probes
Try a probe with a finer point to improve contact inside the connector.

Checking Motor Torque Control

So that there is no call at the thermostat terminals – Remove R thermostat lead and communication plug
115 VAC power should be ON.
Close Blower door switch.
With meter set to volts DC (VDC), insert meter probe into the Molex connector with the yellow wire of PL16.
This Plug located on the PCB has Yellow and Brown wires going to the Motor Plug.
Touch other meter probe to COM on furnace control With no motor operation, voltage will be between 10 to 12 VDC.
Voltage for the speed control is fed from the furnace control at the brown wire, through the motor circuitry, and back on the yellow wire.
If voltage is 0 VDC or significantly below 10VDC then this indicates a likely issue with the connections at the molex plugs at either PL13 or PL16.

Dip Switch Nomenclature

SW1

1 RCL
2 LHT = Low Heat Operation
3 LHR = Low Heat Rise
4 C/E = Comfort Efficiency Adjustment
5 CFM = CMF per ton Adjust
6 TST = Component Self Test
7 DLY OFF = Blower Off Delay 90 Seconds
8 DLY OFF = Blower Off Delay 180 Seconds

SW2

1 TWN = Allows for selection of furnace Main (OFF) or secondary (on) when Twinned furnace setup is required.
2 CFM See Page 37 of 58CTW Installation Manual for adjustments.
3 CF
4 CF
5 CF
6 A/C
7 A/C
8 A/C

Lastly

Check motor winding Resistance
All windings should have resistance values less than 20 Ohms
Winding resistance should be equal +/- 10%
We checked the voltage at the plug connecting the power to the choke from Printed Circuit Board P.C.B.).
Then we bypassed it to verify if the power choke is good or bad.
Next we verified 15 vdc on the brown wire on PL16.
We then verified 10-12 vdc on yellow wire on PL16 when the blower motor not running and 6 to 8 vdc when the blower motor was running.

3/4 hp & 1 hp PWM blower motors have a power choke located on the blower housing
Power chokes are used to filter line power and to reduce current draw of the motor. Power choke may be bypassed for troubleshooting purposes.
Open the blower door switch
Disconnect L1 feed to power choke
Insert meter probe into the L1 connector from the furnace control
Manually close blower door switch and verify 115 VAC power
Release blower door switch
Reconnect L1 to power choke

Then open the blower door switch
Disconnect black lead between power choke and motor
Insert meter lead into disconnected power choke lead
Manually close blower door switch and verify 115 VAC power from power choke
Release blower door switch
Reconnect power choke lead

Power choke may be temporarily bypassed for troubleshooting
Open blower door switch.
Resistance should be greater than 0 and under 1 with no resistance to ground

Checking for Secondary Voltage

Manually close blower door switch and verify 24 VAC between R and Com at thermostat terminals of furnace control
The PWM blower motor used in the current furnaces is controlled by switching OFF and ON a DC voltage (and resultant current) through the motor controller

Checking 15 VDC Power to Blower

Verify all harnesses are connected and 115 VAC power is ON Close Blower door switch
Set meter to volts DC (VDC)
Insert meter probe into the back of brown lead of PL16
Touch other meter probe to COM on furnace control
Voltage from furnace control should be about 15 VDC at the brown wire

Aluminum Fin Surface Oxidation On Air-Cooling Coils

Mon, 12 Aug 2024 18:27:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Aluminum Fin Surface Oxidation On Air-Cooling Coils

The Emergence of White Flakes

The development of large amounts of flakey, white powder from indoor coils has been a recognized industry issue for a couple of decades now. The first known occurrences were reported in residential heat pump systems using refrigerant as the heat transfer fluid. Common characteristics of these cases include coils constructed with bare aluminum fins in air cooling or dehumidifying applications. The problem typically surfaces during the heating season, within the first couple of years of the equipment’s operation, when the dehumidifying coil’s fin surface is dry of condensate.

Spread of the Issue to Commercial Equipment

Although more common in residential systems, this issue has also been reported in large commercial equipment applications and chilled water systems in light commercial and terminal products. Over the last 10 to 20 years, it has been observed that any dehumidifying coil with bare aluminum fins operating in a system that supplies forced air heating during the winter season is susceptible to producing white flakes.

Environmental Factors and Affected Areas

The issue is more prevalent in humid or milder climates that experience severe cooling seasons before the development of the problem. Various applications, including those using chilled water, chilled glycol solution, or volatile refrigerant, have demonstrated the capability to produce white flakes. These cases have not been reported in dry, arid climates or on coils used only in heating applications with hot water, hot glycol solution, or steam.

Once the coil has been installed and operated for a few cooling or heating seasons, its vulnerability to producing white flakes is drastically reduced. The problem has only been reported within the first one or two heating seasons and has not yet been reported during a cooling season. It is suggested that the coils may still produce white flakes during the cooling season, but the condensate on the fins, formed from dehumidifying the airstream, prevents the powder from becoming airborne and, thus, from being detected.

Addressing the Issue

Since no single source of the problem has been identified, the most common approach to mitigating it has been to address the coil producing the white flakes. While the coil may not be the root cause, it is the source of the flakes, making it the most likely starting point for troubleshooting. Replacing the coil with an identical one could allow the condition to return, although this isn’t guaranteed as job site conditions may change over time.

Customer Complaints and Mitigation Strategies

From a customer standpoint, the main complaint has been the housekeeping issue of white powder being distributed from the HVAC ducts and diffusers. Post-filtration or final filtration has been successfully applied to contain the flakes within the air handler systems or ductwork. While not all systems are conducive to additional filtration, it has been shown that even minimum particle-efficient filters are capable of removing the large white flakes from the airstream. Field experience has shown that coil cleaning, at best, offers only short-term relief, as flake production will inevitably return.

Permanent Solutions: Coil Replacement and Coatings

Replacing the affected coil with one that has coated aluminum fins can eliminate the problem. Common coatings include corrosion-resistant coatings, which are optional on some product lines. While this is relatively easy to accomplish in residential equipment, it requires much more effort, time, and cost to replace coils in large commercial equipment. Using alternate materials for the fin surface, such as copper or steel, will also prevent the formation of white flakes since there is no aluminum material.

There is no known material treatment or coil cleaning process that will stop the chemical breakdown reaction causing the flakes. Evaluating job site conditions, such as chemical treatments and cleaners, indoor pollution, or outdoor pollution, could help determine causal relationships. Source control of the reaction catalyst will be the best approach to successfully eliminating the problem from reoccurring in the building.

June 10, 2026

Have you ever received a call from a customer about “white flakes,” dust, or particles blowing out of ductwork in residential or commercial settings? You may have tried to resolve the issue by cleaning the coil or installing ultraviolet lamps, but the “white flakes” keep coming back. This is a known issue in the HVAC industry, and it’s more common than you might think.

Heat Stroke Symptoms & Hydration Tips

Mon, 12 Aug 2024 18:22:00 GMT

Anthony Coker

VRF Tech Support and Quality Assurance • North Georgia, North Alabama

Heat Stroke Symptoms & Hydration Tips

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Water plays a crucial role in maintaining your body’s health. It helps keep your body at a normal temperature, lubricates and cushions your joints, and protects your spinal cord and other sensitive tissues. To increase your water intake, consider carrying a water bottle with you and refilling it throughout the day. Choose water over sugary drinks, and add a wedge of lime or lemon to enhance the flavor. When dining out, opting for water can help you save money and reduce calorie intake.

Heat Stroke Symptoms

Heat stroke is a serious medical condition that happens when the body fails to control its temperature, often due to prolonged exposure to extreme heat or intense physical activity. Common symptoms are:

Mental status changes: Confusion, delirium, combativeness, slurred speech, or loss of consciousness
Body temperature: Core body temperature above 103°F (40°C) or higher
Skin: Hot, red, dry, damp, flushed, or very pale skin
Other symptoms: Headache, dizziness, nausea, vomiting, rapid and strong pulse, seizures, or convulsions

If you suspect someone is experiencing heat stroke, you should call 911 or get them to a hospital immediately. While waiting for emergency services, you can try to:

Move the person to a cooler, shaded, or air-conditioned environment.
Remove any outer clothing.
Reduce their body temperature with cool cloths or a bath.
Use a fan if the heat index is below the high 90s.

If someone is conscious and alert enough to swallow, you can give them chilled water to drink if they are experiencing heat stroke. You can also try giving them a sports drink with electrolytes or another nonalcoholic beverage without caffeine. If you help them drink, make sure they are sitting up, so they don’t choke. However, most people with heat stroke have an altered level of consciousness and shouldn’t be given fluids.

Give yourself extra time to take breaks. Don’t wait until it’s too late! Another tip for keeping cool is to get a cooling towel to wrap around your neck and a fan to set up and circulate some cooler air from below the attic.

As you all know, working in the AC business doesn’t always mean working in air conditioning! In this article, we want to show you the symptoms of heat stroke and ways to stay hydrated. An attic’s temperature can rise well over 125 degrees when the outside temperature is only 90 degrees.

Stay hydrated by drinking plenty of water. You can even find flavor packets to mix in and create just about any taste you like.

Water Blowoff

Mon, 12 Aug 2024 18:03:00 GMT

Anthony Coker

Technical Service Manager

Water Blowoff

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Water blowoff is caused by unconditioned air entering the return air stream from leaks in the return duct, wall penetrations or anywhere unconditioned air can infiltrate the return air supply. Normal return air is at about 50 to 55% relative humidity with the system operating normally. Infiltration in the return adds water vapor and increase the RH to 60% or more in the return air.

This added humidity load increases the water load on the surface of the coil and decreases the airflow through the coil, causing more draw from the blower section. This increase in draw also increases velocity of air moving through the coil fins pulling water with it.

This problem is more apparent with variable speed air handlers because variable speed motors will not slip as static across the coil increases with the water load. Non variable speed motors will slip or pull less air as static increases.

High velocity air also increases the chances for water blow off. Duct systems that has air exceeding manual “D” recommended air velocities will have water blow off problems and sweating ducts.

Recommended velocities (F.P.M.)

Flex – 600-800 FPM Main supply

– 400-600 FPM Branch supply

– 500-700 FPM Return Main duct

– 300-500 FPM Return Branch duct

Metal Ductwork – 700-900 FPM Main Supply

– 500-700 FPM Branch Supply

– 600-800 FPM Return Main duct

– 400-600 FPM Return Branch duct

The duct system must be sized properly not to exceed a -.2″ return static and .3″ supply static, with a .5″ total external static at less than 700 FPM with filters and grills installed.

Equipment capable of controlling moisture is readily available; the problem has been the lack of an affordable and dependable sensor feedback control for measuring latent content of air. The right thing to measure in buildings is dew point.

Introduction to Duct Design & Static Tips

Fri, 12 Jul 2024 14:18:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Introduction to Duct Design & Static Tips

What all goes into “duct design”? Most important is having a balanced system, meaning what comes in (return) must go out (supply). An old school way of thinking is 400 CFM per ton. Several years back, Carrier started designing their CFM charts for 350 CFM per ton, and moving forward, that is how we should also look at our systems that we are replacing or redesigning. Included in the article is an example of a 2.5-ton system and some best practices on sizing. There is also a chart that lists how much CFM a certain-sized duct will flow. Please take careful note of all the text in the example system, as there are a lot of best practices listed there.

Blower CFM Chart and Static Pressure

I took from a common 3-ton furnace installation manual the CFM Blower chart. Checking for static pressure and changing your speed taps on your blower is vital to flowing the proper CFM per ton and helping the longevity of both the indoor blower motor and outdoor compressor. Prior to 2023, unit rating tests for SEER1 were performed at 0.2” static. Then starting in 2023 Jan 1st the SEER2 is now tested at 0.5” static. In a real-world scenario, this is hard to recreate. This is another reason why checking static and blower speed is very important. You can still achieve 350 CFM per ton if your static is above 0.5 by changing blower speeds, but most importantly, perhaps, is the duct sizing.

Filter Pleating and Airflow

Some key things to realize as well are your filter pleating. When it comes to a standard 1” filter, most people think that an expensive allergy-rated filter is better for you, but in all actuality, it is hurting the airflow of your system and causing strain on key mechanical components. A middle-of-the-road 1” filter is all you need for proper airflow. Media type filters are a little different, as they allow better filtration and better airflow. Another thing to note is proper filter sizing.

Filter Pleating and Airflow

• A 16×25 opening only allows for a maximum of 1400 CFM. That’s about a 3.5-ton max.

• 20×25 openings allow for approximately 1600 CFM, which would be a 4-ton max.

• Lastly, if you have a 5-ton unit, it is critical to have dual returns to bring in the proper amount of return air

If you have any questions about the airflow charts in the residential furnace manuals please direct them to 770-239-2130.

Sizing your Ductwork

Default Carrier setting 350cfm per ton

June 10, 2026

See below for a typical example of a 2.5 ton unit.

875cfm at .5 static.

Cfm chart above is for a standard comfort series 17 wide 3 ton furnace.

STATIC PRESSURE MATTERS!!! Duct design matters for proper operation of equipment.

Return and supply must be balanced. 1050cfm for both.

Carrier VRF OH7 Error Code

Wed, 10 Jul 2024 16:30:00 GMT

Anthony Coker

VRF Tech Support and Quality Assurance • North Georgia, North Alabama

Carrier VRF OH7 Error Code

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

On this video we will be covering the following topics

Error code 0H7
Setting the outdoor unit to be able to see the correct number of indoor units
Setting a custom address
How to set an address using the wireless remote.

Dirty Sock Syndrome

Tue, 09 Jul 2024 20:32:00 GMT

Anthony Coker

Technical Service Manager

Dirty Sock Syndrome

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

What It Is and Isn’t

Dirty Sock Syndrome isn’t about flawed design or material in HVAC systems. It’s a term that might not be familiar, but the phenomenon is unmistakable. When an air conditioner emits a moldy, foul odor that resembles dirty gym socks, it’s a clear sign of Dirty Sock Syndrome.

Identifying the Smell

The smell of Dirty Sock Syndrome varies but centers around decaying organic material. Technicians often find that homeowners become desensitized to the smell due to constant exposure, similar to how individuals get used to their own body odor. The odor is usually more noticeable after the house has been unoccupied for a few hours.

Causes of Dirty Sock Syndrome

This syndrome is caused by mold and bacteria accumulating on the evaporator coil. Continuous moisture promotes mold and mildew growth, while dust particles contribute to the problem due to poor filtration.

Detecting Dirty Sock Syndrome

While the distinct smell is a primary indicator, other issues can also cause bad odors. Technicians should first rule out other potential problems. Check and ensure that drainage pans are empty and free from rust and damage. Clear any blockages to prevent mold and mildew growth. Wet filters and blocked drainage lines also indicate issues.

Risks Associated with Dirty Sock Syndrome

While not usually dangerous, Dirty Sock Syndrome can pose health risks if mold spreads through the HVAC system. This can cause respiratory issues and eye irritations. It’s important to address the issue promptly to prevent the odor from affecting the household’s well-being.

Preventing and Treating Dirty Sock Syndrome

Prevention is key. Always use high-quality filters and replace them every one to three months. Installing UV air purifiers can prevent mold and bacteria from compromising the evaporator coil. UV lights effectively kill mold spores and bacteria, providing additional protection for the system.

If Dirty Sock Syndrome is already present, start by cleaning the evaporator coil. Although homeowners can attempt this with homemade solutions, it’s best handled by professionals trained in HVAC cleaning. Replacing clogged or wet filters ensures proper filtration and airflow. Technicians may also need to clear blocked drainage lines, often with a shop vac.

Sources:

HAVC Partners, POL224.00 APP Guide, IIK-CRECON-SRT-01

Infinity/Evolution Server Connection Issues

Mon, 10 Jun 2024 20:25:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Infinity/Evolution Server Connection Issues

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

The most effective solution to correct the server connection issue is to connect to a dedicated 2.4G router. Connecting a wireless router involves several steps, but don’t worry, I’ll guide you through each one. Here’s a detailed explanation:

1. Unbox the Router: Open the packaging carefully and take out the wireless router along with its accessories, including the power adapter, Ethernet cable, and any documentation or installation guides.

2. Choose a Suitable Location: Decide where you want to place your router. Ideally, it should be in a central location within your home or office to ensure maximum coverage. Also, try to keep it elevated and away from obstructions like walls, furniture, and appliances that can interfere with the signal.

3. Connect to Power: Plug the power adapter into an electrical outlet and connect the other end to the power port on the router. Ensure that the router is receiving power by checking for any indicator lights on the device.

5. Connect to Modem: If you have a separate modem (provided by your ISP), you’ll need to connect it to the router using an Ethernet cable. Plug one end of the Ethernet cable into the Ethernet port on the modem and the other end into the WAN (Wide Area Network) or Internet port on the router. This connection allows your router to access the internet through the modem.

6. Power On: Turn on the router by pressing the power button (if available) or simply by plugging it in. Wait for a minute or two for the router to boot up completely. During this time, the router will perform self-checks and establish connections with your modem and other devices.

7. Connect Devices: Now that your wireless network is set up, you can connect your Infinity/Evolution controller.

8. Wi-Fi Setup: Enable Wi-Fi under settings, scan for access points, and chose the new router from the list. Enter the password that came with the new router, and watch it connect.

That’s it! Your wireless router should now be successfully set up and ready to use.

Siemens POL224.00 Economizer Controller LED Indication

Mon, 10 Jun 2024 20:12:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

Siemens POL224.00 Economizer Controller LED Indication

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Have you ever wondered what the LED’s are used for? In this article we will discuss each one and what the difference colors represent. There are three LEDs located on the face of the controller just below the display screen. From left to right you will see a Snowflake, a Temperature Sensor, and a Damper Actuator symbol.

LED Indication

Number 1 LED is for Free Cooling, Number 2 is for the Sensors and Number 3 is for the Damper Actuator.

In the charts below you will see the status of each LED and what they represent.

Now we will discuss some of the common systoms that you will see and the possible causes and solutions.

Symptom- Brownout Protection Mode. If the voltage is below 17 VAC, the Economizer Controller will go into this mode. This mode diables all of the relay outputs. When the power is 19 VAC or higher, the Economizer Controller will operate normally.

Symptom- An alarm is dispalyed on the LCD screen. Possible issue is sensor, damper, or the whole working system may not work properly. Check sensor, damper, or the whole system following the detailed alarm imformation per the manual.

Symptom- DAC LED is blinking RED. Possible issue is Damper slippage. Check whether the damper works properly. Symptom- DAC LED is blinking RED very fast. Possible issue is that the damper is unplugged. Check whether the damper is connected.

Symptom- DAC LED is OFF. Issue is that there is no feedback signal to the controller. Check whether the feedback signal is connected.

Symptom- Sensor LED is solid RED. Possible issue is Mixed Air Sensor or Outside Air or Return Air Sensor configuration, must be either Type II NTC 10K or 0-10 vdc sensor.

Symptom- Sensor LED is YELLOW. Possible issue sensor connection, sensor type and signal.

Symptom- Sensor LED is OFF. Possible issue is CO2 sensor connection, sensor type and sensor signal type.

NOTICE:

If different fault events occur at the same time, Sensor/DAC LED lights up following the priority below:

RED (Fast Blinking) – RED (on, Steady) – RED (Blinking) -YELLOW-Off- Green. For example, if there is a humidity sensor error and air temperature failure at the same time, the Sensor LED turns red rather than yellow.

Also, after the controller enters the running state mode, it may take one minute for the peripheral devices to complete initialization. Before that, LED indication might be unstable.

Sources:

HAVC Partners, POL224.00 APP Guide, IIK-CRECON-SRT-01

Installing Carrier VRF Part 3

Mon, 10 Jun 2024 19:51:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Installing Carrier VRF Part 3

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Last month we covered how to electronically address a system. But why? What is the importance of this? Let’s find out.

When you are installing a VRF system there are typically many moving parts in terms of communication and control. Electronic address allows ODU, Touch Screen, and Bac-Net to see what a particular unit is doing. Again, an identifier.

From the above picture you can see the electronic address #2 on ODU #1 is off on an EE error and ODU #2 has 2 errors of DD. EE is a water trouble, probably a clogged drain or something wrong with the pump (if equipped). DD is a mode conflict on Heat Pump systems when 2 units are in different modes. This can also happen on Heat Recovery when 2 ports are merged on the MDC box trying to run in different modes.

This information will show on not only the units themselves but also the Touch Screen and Bac-Net. With proper documentation during install these problems can be easily found and solved when it is time to troubleshoot.

40VM90006

40VM90006 A

When pulling units into a central controller pictured above the electronic addresses are where everything comes in and ties together in the INSTALL MENU. From this point you can manually control the system by ODU, IDU, or as an entire group. If duplicate addresses or aren’t set, they won’t pull into the touchscreen and ultimately Bac-Net. This is where everything ties together and works in sync with each other.

One other thing to keep in mind is when installing a Heat Recovery is if there is more than one MDC box than the Sub-MDC needs to be addressed via the S8 dipswitch and if there are any merged copper ports. If copper ports are being merged for any reason than the corresponding switches need changed.

Here is some information regarding MDC address and copper port merge:

With this information you should be well on your way to successfully installing a Carrier VRF system. HVAC Partners is a great place to get information for both Service and Install in case the manuals have been lost. HeatCool.com is another place to gain information with tips and tricks from your favorite Technical Service team, Mingledorff’s.

Have a great day and stay safe!

Ecobee Dehumidification Control

Mon, 20 May 2024 17:08:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Ecobee Dehumidification Control

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This section describes how to setup an ecobee thermostat to control a standalone dehumidifier or a forced air furnace/air-handler that supports a ‘Dehum’ mode.

Once the ecobee has been wired to control the HVAC system and dehumidification system using the ACC+/ACC- terminals it will require correct setup to determine how you want to enable Dehumidification control. During the first-run setup they are a few key settings to ensure Dehumidification is part of the HVAC control algorithms.

After the ecobee has been configured there are a few specific settings that allow you to determine when the Dehumidifier becomes active.

To access these settings, on the device select MENU > SETTINGS > INSTALLATION SETTING > EQUIPMENT > DEHUMIDIFIER.

Siemens Economizer Setup

Mon, 20 May 2024 16:58:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

Siemens Economizer Setup

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

In this article we will cover the basic set up options needed for the field installed EconomizerOne Accessory for Small Rooftops Units 3 to 12.5 Tons. The EconomizerOne comes standard with an outdoor temperature sensor and a mixed air temperature sensor (also called supply air temperature sensor).

You will make all selections using the User Interface. It has a One-Line LCD display screen, three operations buttons, Up Button, Down Button, and the Enter Button.

Menus are displayed in the Economizer Controller as per categories. There are eight first-level menus, each of which is represented by a number at the beginning of the line on the LCD. Pressing Enter plus Up or Down can toggle between different first-level menus.

Submenus follow the numbered first-level menus closely. Pressing Up or Down can toggle between different submenus.

At the end of the line, the LCD displays the value of the current submenu (if any). If the value is editable, pressing Enter enters the Edit mode. The value is then highlighted for change. After making a change by pressing Up or Down, press Enter to confirm the change and exit the Edit mode.

Before you start, make a note of the type of unit you have, example:

2 speed indoor fan

2 stages of cooling

outdoor air-dry bulb temperature sensor

Press the Up button twice to enter the 5CONFIG STATE , then Press Enter to the enter the 5CONFIG STATE , then press Enter again to confirm that you would like to enter this menu. The controller display screen will go blank, then it will display 6OCC menu.

Next press the Down button to the 6Y2O menu, this sets the number of cooling compressors, the default is COOL 2 (2 Stage). If your unit only has one compressor, change to NONE for 1 Stage. Press the Enter button, use the Down arrow button to change, then press the Enter button to confirm.

Next press the Down arrow button to 6FAN menu to set the number of indoor fan speeds. The default setting is 2SPEED. If your unit has 1 speed, 3 speed, or VFD, you will change the selection here by pressing the Enter button, then the using the Down arrow button to change the selection, then press Enter to confirm.

Next press the Down arrow button to the 8RUN STATE menu, press the Enter button twice. After a few seconds the controller will reboot.

Since we are using an outdoor air temperature sensor, so next use the Down arrow button to the 2TEMP OFF menu. This is the high temperature setting that limits the use of free cooling. The default setting is 63 F. (The most common setting is 55 F). To change, press the Enter button, then use the Up or Down arrow buttons to advance to desired temperature and press the Enter button to confirm.

Next using the arrow buttons, go to the 2FAN L ACT menu to set the minimum damper position when not in the free cooling mode and with a fan in low speed. The default setting is 3.6 V. Lower the voltage, less open of the damper and higher voltage the more open of the damper. To change, press the Enter button, then use the Up or Down arrow buttons to advance to desired voltage and press the Enter button to confirm.

Next using the arrow buttons, go to the 2FAN H ACT menu to set the minimum damper position when not in free cooling mode and with a fan in high speed. The default setting is 2.8V. Lower the voltage, less open of the damper and higher the voltage, more open the damper. To change, press the Enter button, then use the Up or Down arrow buttons to advance to desired voltage and press the Enter button to confirm.

Next using the arrow go to 5RESTART mode, then press Enter twice. This confirms all changes and restart the controller.

Sources:

Sources: POL224.00 Application Guide, HVACPartners (IIK-CRECON-SRT-01)

MicroMetl Corporation; link https://www.youtube.com/watch?v=ZEFPB9Fh-h8

Installing Carrier VRF Part 2

Mon, 20 May 2024 16:47:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Installing Carrier VRF Part 2

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Last month we covered the importance of labeling and documenting on a Carrier VRF Heat Recovery system. Documentation during Installation is key in the end success of any of these systems. This month we will cover electronic addressing.

Electronic address, not to be confused with port address, is the address assigned to a unit to signify where it is and can play a very important role especially in the case of external control such as I-Vu or any other 3rd party control company. The easiest way this can be explained is this: The ODU is your house, each IDU is a room in your house. You basically tell each IDU what “room” it is with electronic addressing.

With Carrier VRF there are several ways to address a system. Heat recovery systems can be addressed by using a wired or wireless controller. They are as follows:

40VM900003 – Wired Programmable control.

Enter the Service and Startup menu by pressing “Back” and “Fan” buttons at the same time until the advanced menu.
Scroll down to the 3rd menu and go into “IDU Addressing”. Select the number and hit “OK” in the center of stat.

40VM900002 – Wired Non-Programmable Control

Hold “Room Temp” and “Swing” at same time for 3 seconds.
Press “Temp up/Down” to set address and hit “OK”.

Press “Fan” and “Back” at the same time for 5 seconds to enter service menu.
Press “Temp up/down” and go to “IDU Addressing”. Hit ok.
Use “Temp Up/Down” to select address and hit “OK”.

40VM9000001 – Wireless Remote

Push “Lock” button at bottom left of control for 10 seconds. A small tool like a pen or solid stat wire will work.
Press “Power” after the 10 second hold.
Press “Up/Down” to select address.
Press “Fan” to confirm and send to unit.

Bear in mind that the wireless remote option requires the use of the display board and works well for 4-way cassettes in high ceilings.

Now that we have an address set for each IDU we need to make sure a few things. We need to ensure while doing the addressing that we not duplicate addresses except for in very few circumstances. This information should be notated somewhere like on the MDC as explained last month in Heat Recovery. Heat pump systems do have the ability to auto address via the “S6” (3 phase) and “SW4” (1 phase) Dipswitch bank in the ODU on the Main board. Factory default is auto search (Off Off) on the switch bank.

3 Phase:

1 Phase:

Now that we have the IDUs addressed what next?

If the systems are going to be on a Bac-Net or touch screen, the ODU needs to be addressed as well. This is easily accomplished by changing ENC 4 on 3 phase units and ENC 2 on 1 phase units.

With all the addressing setup you just need to turn it on and get the system going. You can see why labeling and documenting any changes made can be very important. Once you make changes on a system with more than 10 IDUs things can get confusing very quickly.

Don’t forget to change ENC3 + 12 on the ODU main board to indicate how many IDU’s are connected and communicating!

Now you have addressing setup and ready to roll. What have we done? Find out next month what all this means.

Ecobee Free Cooling

Mon, 15 Apr 2024 18:35:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Ecobee Free Cooling

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

The ventilator control capabilities depend on the type of ventilator installed which can be either a HRV, ERV or standard Ventilator.

There minimum runtime setting when the home is occupied and when unoccupied. The ventilator will also run for 60 minutes prior to occupancy, this is called pre-purge and is not user adjustable but can be enabled or disabled.

Regardless of the type of ventilator the minimum runtime settings are used to force the ventilator to run a specific number of minutes per hour. This runtime is broken into 15-minute blocks to evenly spread out the runtime throughout the hour, but at a minimum 5 minutes of runtime is required. So, if the runtime was set to 10 minutes, the time is broken into two 5-minute blocks.

Free Cooling: If a standard ventilator is installed, then it can be used to cool the house and is much cheaper to use compared to air conditioning. The thermostat will look at indoor temperature and humidity and outdoor temp and humidity to determine if free cooling can be used. If conditions are favorable, then the ventilator will be engaged instead of the air conditioner. There are several configuration settings used to control free cooling. This feature does not apply to a HRV or ERV. To access these, Select MENU > SETTINGS > INSTALLATION SETTINGS > EQUIPMENT > VENTILATOR

Installing Carrier VRF Part 1

Wed, 10 Apr 2024 20:24:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Installing Carrier VRF Part 1

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Getting to know how a system works and what tools you have to solve common issues is a huge challenge in VRF. Today we will explore the install side of Carrier VRF to help prevent issues that may arise before the job is completed.

Some of the most common problems start right at the install of any VRF system. One of which we discussed towards the end of last month’s article regarding communication and ports being swapped on a Heat Recovery system. There are ways to help prevent this during install and minimize or even alleviate this issue all together.

From this picture below you can see that inside the MDC box there is A LOT going on:

This box provides you with simultaneous heating and cooling inside a space through a series of solenoids valves, EXVs, and communication wires to control it all. This is why it’s vital to communicate and document everything that is done to this box. I’m going to give an example below, and make this significantly easier for anyone to understand.

Port address is also known as the copper address. This is in reference to the copper stubs coming out the back side of the MDC box. Every copper port on the MDC has a number corresponding to it and is labeled inside where wiring attaches.

Electronic address is exactly as the name implies. It’s an electronic identifier used for labeling each indoor unit on the system. This is usually set via the thermostat, wireless remote, or in the case of Heat Pump, Auto Addressing. This is commonly confused with port address, and the two are rarely the same.

Room number or reference ID of an indoor unit’s location is vital in case an issue arises with any particular unit. This is highly recommended as it gives a good middle area between port and electronic address in case something gets confused. If you have the port addressed and the room referenced, the electronic address can easily be located and changed, if needed.

With this written on the MDC box, it gives a lot of information that can be quickly referenced when doing commissioning or service work. The crossing of communication wires from port to port is much less likely and makes finding them significantly easier.

Line length in the picture above can help with charging of the system and can be valuable later if a particular indoor unit has issues and needs replacing. This is the main reason we recommend and supply ball valves with every MDC box when purchased through Mingledorff’s. Having line lengths written on the MDC helps to translate back to a program called Vroom (becoming Vpro) that gives an indication o the additional and total refrigerant charge of the system.

I can’t stress enough how important proper documentation is when installing a Heat Recovery VRF system. The more information that’s kept documented and accurate the better for the flow of the job. A little extra time now saves a lot of time later.

I hope this article gives a bit of insight on installing a Carrier VRF system. Next month we will cover how to and why electronic addressing is important to any VRF system. What is the purpose? Where does it all tie in?

PWM Furnace Blower Motor Troubleshooting

Wed, 10 Apr 2024 20:01:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

PWM Furnace Blower Motor Troubleshooting

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This month I will be covering how to troubleshoot a PMW Blower Motor on a Carrier furnace.

What is a PWM motor? The acronym PWM stands for Pulse Width Modulation. For motor controllers, PWM can refer to both the input signal and the method the controller uses to control motor speed.

The blower motor has 115 VAC applied to it anytime the furnace is powered, so you will need to verify this. Manually close the blower door switch and measure the voltage between L1 and Neutral L2 wires as shown below on the control board. (Note; If 115 VAC is not present, check incoming power to furnace.)

Open the blower door switch, disconnect black lead between power choke and motor. On ¾ & 1 PWM horsepower motors will have a power choke located on the blower housing. Power chokes are used to filter line power and to reduce current draw of the motor. The power choke may be bypassed for troubleshooting purposes. Insert your meter lead into disconnected power lead and manually close the blower door switch. Verify 115 VAC is present. If correct voltage present, open blower switch and reconnect power leads.

Checking for secondary voltage, the PWM blower motor used in the current furnaces is controlled by ON/OFF switching of the DC voltage circuit through the motor controller (CPU).

Manually close the blower door switch and verify 24 VAC between R and C at the thermostat terminals on the furnace control board as shown below.

Now you will need to check 15 VDC Power to Blower Motor. Verify all harnesses are connected and 115 VAC power is on. Close blower door switch. Set your meter to DC volts (VDC). Insert positive probe into the back of brown lead at PL16. Touch the other lead to C terminal on furnace control board. Voltage reading from the furnace control board should be about 15 VDC at the brown wire as shown below.

L1 harness connected to blower motor

There are only two wires to control motor speed, brown wire feeds constant 15 VDC to the motor and yellow wire feeds back from the motor to the furnace control board.

Note: a reading of approximately 35V (or higher) indicates the green ground wire on the motor is disconnected – repair as needed.

A 15 VDC reading is normal, may be slightly higher or lower as actual line volage affects low voltage. If measure voltage is unstable or scrolling, check harness connectors and pins.

Checking motor control signal, with no call for Fan from the thermostat, close the blower door switch. Your meter set to DC voltage (VDC), insert the positive lead into the back of the yellow lead of PL16. Touch the other lead to the C terminal on the furnace control board. With no motor operation, voltage will be 10 to 15 VDC as shown below.

If voltage is 0 VDC or significantly below 10 VDC:

0 VDC indicates a likely “no connection” issue with the harness connector plugs at either PL13 (Motor) or PL16 (Harness)

Voltage significantly below 10 VDC indicates partial connection of harness connectors, or a damaged motor controller.

Checking the motor control signal, close the blower door switch and a call for Fan only from the Thermostat. Your meter set to DC voltage (VDC), insert the positive lead into the back of the yellow lead of PL16. Touch the other lead to the C terminal on the furnace control board. With the motor operating, voltage reading will 5 to 8 VDC as shown below.

Remove the call for Fan, voltage reading will return to 10 to 15 VDC when the motor turns off.

Sources:

HVAC Partners, 59SC6A-01SI

Servicing Carrier VRF Part 3

Mon, 18 Mar 2024 14:47:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Servicing Carrier VRF Part 3

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Over the past 2 months, we have covered how to connect to a Carrier VRF with STT software and what to look for. What are some of the most common problems and solutions? Let’s take a look.

First, let’s look at the FE#0 code. This error code exists on the thermostat when the IDU hasn’t been addressed. This can lead to system malfunction and is required for all system types especially if Bac-Net and I-Vu are involved. This can also lead to the 0H7 error code (see below). Simply address the indoor unit and make sure all are different from any others, 1-64. Keep in mind that any IDUs that are sharing a thermostat each IDU needs it’s own address. There are 2 different actions that can be done to accomplish this: Wireless remote with the display board or isolate the IDUs from each other and utilize the advanced install menu.

One common call we get in Technical Support for VRF is the famous 0H7 error on the ODU. OH7 is referencing that ENC 3 + S12 quantity on the ODU doesn’t match the quantity of IDUs that the system sees. Solution: verify ALL the IDUs have main power connected, ensure communication wiring is tight and landed on proper terminals, all indoor units are addressed, and most importantly, setting ENC 3+S12 settings in ODU located on main board (3PH ONLY).

Picture it. You have the entire system powered and addressed, service valves are open, STT is connected and up on your computer, Indoor units are calling for heat, nothing is running. No errors? Outdoor unit won’t even try to come on…. but why?

STOP! DON’T FREAK OUT!

Have you had the outdoor unit powered for a minimum of 24hrs? Probably not. An algorithm built into the outdoor unit won’t even try to come on until the compressor oil has reached a certain temperature. My advice to installing technicians is to get main power connected to the outdoor unit and turn it on. Save yourself a day worth of wait. You’ll thank me later.

If there is anything that I can stress to technicians working on VRF, be patient!

Also, keep in mind that when you turn power on to the ODU that there is a 12 min time delay before it will even start to think about running. This is a good time to get your workspace setup and organized, take panels off, etc. And on a side note, if the system you are working on is a heat pump, heat mode won’t activate above 65F ambient outdoor temp. Outdoor unit won’t even try.

Moving on. Everything is on and there’s an E6 error on one of the cassettes…

IDU DC FAN ERROR? THIS UNIT IS BRAND NEW?!? BAD FAN MOTOR ALREADY?!?

Breathe. It’ll be ok. Did someone forget to take the shipping blocks out of the blower housing? More than likely. Remove the blocks, power cycle the unit, should be off to the races after. If not, verify the motor is plugged into the board and that you have the proper 208/230VAC going to the unit. If everything above checks out you will need to inquire with the service manual to figure out if you have a bad board or motor. If you’ve been in the industry long enough you know that these kinds of things can happen from time to time.

If you have installed a Heat Recovery system before, then you have more than likely run into this next problem. Room A calling for heat but is cooling, Room B is calling for cool but is heating. During our inspection process we go through something called PORT CHECK. This process we start by putting everything into 1 mode and then one by one turn the various IDUs into heat. In this scenario, more than likely, Room A and B have their P/Q/E control wires swapped in the MDC box. When you have a larger system with 10+ IDUs this problem becomes much more prevalent if attention wasn’t paid during the running of wires. As a rule, when you are going through the system and encounter one IDU not in the correct mode look for the another that is accepting the command. It’s easier to visualize than explain.

Last month we covered how to get the software and your service computer hooked to a system. If you need a refresher or missed that portion you can find it here . When first opening STT (Service Technical Tool) it can be a little confusing how to get started and figure out what exactly you’re looking at or looking for. Today we will be exploring this software.

First and foremost, we need to update our resolution for our computer display to 1366×768 to ensure most of STT fits on the screen.

To do this:

Go to the Start Menu > Settings > Display > Display Resolution > 1366×768 > Keep Changes

You can see that Address 2 goes to 1, 1 to 3, and 3 to 2 by process of elimination.

This concludes the common issues during installation. If there is any questions, please feel free to visit heatcool.com or call the Mingledorff’s Technical Service line.

Defrost Board Troubleshooting

Mon, 18 Mar 2024 14:34:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Defrost Board Troubleshooting

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

I want to go over the process of troubleshooting a heat pump defrost board. This includes checking for common issues. Start by examining the board for visible damage or burnt components. Now we need to use a multimeter to test continuity, voltage, and resistance at various points on the board.

The first place we need to check is to see if we are getting power to the board. Here we are checking for the 24 volts at the contactor.

1. Now we check the board for 24 volts. The T1 terminal on the defrost board powers the defrost timing function. This terminal must be energized before any defrost function will occur.

2. If the unit does not go into defrost after performing the speed up, check for 24 volts on the T1 terminal. This terminal powers the defrost circuit, and must be energized before any defrost function can occur. The T1 should be energized once the Y terminal is energized and the pressure switches are closed. Ensure the T1 wire is connected at the contactor, and that 24 volts is present on the T1 spade terminal.

Check to see if the defrost switch is open or closed. Disconnect defrost thermostat leads from control board, and connect to ohmmeter. Thermostat leads are pink, insulated wires connected to DFT and R terminals on control board. Resistance reading may be zero (indicating closed defrost thermostat), or infinity (OL for open thermostat) depending on outdoor temperature.

Now we want to check for 24 volts on the DFT terminal. Checking that the defrost board is supplying power to the defrost Switch.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

SystemVu Software Update

Mon, 18 Mar 2024 14:30:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

SystemVu Software Update

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

In today’s world of computers, smartphones, electronic devices they require updates for them to operate correctly. The same applies to the HVAC Industry, with units having controllers with software programs that need updates from time to time. In this article we will talk about the process to update the software in the SystemVu controller. The SystemVu is available in the following Models: 48/50FC, 48/50/GC, and 48/50LC.

The SystemVu Software Update Process in simple, below is listed the items that are needed to complete this process.

USB Thumb Drive no larger than 16 Gigabytes in size.
The latest version of software for the unit you are updating from HVACPARTNERS.COM.

In HVACPartners>Dashboard>Post-Sales-Support>Service Software

Once you have downloaded the last version for your unit, unzip the file and copy the SW_IMG folder and paste it on the USB Thumb Drive.

Now that you have the latest software on your USB Drive you are ready to begin to update the controller. Be sure to record your model and serial numbers, you will need them later. Once the USB Thumb Drive is inserted into the USB socket, the device will ask if want to use the USB Options?

Select Yes with the up and down arrows, the press Enter.

The USB Options has 5 options as shown below:

Once you have logged in, you will need to save the equipment current configurations by choosing: “SAVE CONFIGS TO A FILE”. Align the arrow on the SAVE CONFIGS TO FILE option and press ENTER. Then press ENTER to make the STOP flash, use the UP or DOWN arrows to change the STOP to START and press ENTER. Once this is done, Choose Option 5 to UPGRADE SOFTWARE. Then scroll down to “FIND APPLICATION FILE” and press ENTER to change NO to YES.

The update process will start. This will take a few minutes.

Each of the USB Options require a user login. When prompted to Log In, with the ENTER PASSWORD screen. Use the Up arrow twice to change each star to a 1 then press ENTER- do this for all characters.

Then press ENTER to choose the USB Product Folders:

When all the files have transferred the device will restart and installed the update. Once the device has started up you need to verify that Model Number, Serial Number, and other parameters were retained. From the Main Menu select SERVICE, then select UNIT INFORMATION to see if the update retains your model and serial number. Then select SAVE CONFIGS FILE and select YES to find the .CSV file with same last four numbers of the serial number. This will restore the configurations saved prior to the update.

Press Enter and the congregations will be restored. The update process is now completed. The system will should operate normally. You have successfully updated the software for your SystemVu.

Sources:

HVAC Partners

Then select the Product Software: Once selected press ENTER.

Freeze Protection mode

Wed, 14 Feb 2024 15:44:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Freeze Protection mode

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Freeze Protection Alarm description, pulled directly form the manual:

“Coolers can be ordered with heaters installed in the factory. If equipped, the main base board based on the outdoor-air temperature and the entering and leaving water thermistors controls the cooler heaters. The Heater Set Point is the sum of the freeze point and Cooler Heater DT Setup (Configuration>SERV>HTR). If the entering or leaving water temperature is less than the Heater Set Point and the outdoor-air temperature is less than the Heater Set Point – 2°F (1.1°C), then the heater will be turned on. If the Entering or Leaving Water Temperature is less than the Brine Freeze Setpoint (Configuration>SERV>LOSP) + 1.0°F (0.5°C), then the heater will be turned on along with the pump.

If the cooler PUMP/PUMPS are not hard wired to the chiller control panel, this most important feature of the Carrier freeze protection routine is disabled.

In addition to the cooler PUMP freeze protection routine, the entire cooler is covered with closed-cell insulation applied over the heater.

Heater, plus pump control, plus insulation protect cooler against low ambient temperature freeze-up to –20°F (–28°C).

The Chiller control system will try to protect the barrel from freezing in very low ambient conditions. This is not the best way to combat Freeze issues if your machine is running fresh water.

The best 2 methods are either draining the chiller of all water when it’s not in use or adding an antifreeze to the chilled water loop, suitable to Protech against your outside air temps.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

With outdoor air temps dropping below freezing around Georgia and the southeast, there is a chance you have walked by a 30 series chiller that was indicating (ALARMS) saying the phrase Freeze Protection Alarm has been activated.

Ecobee Setup

Wed, 14 Feb 2024 15:31:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Ecobee Setup

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Ecobee thermostats provide multi-speed fan control to work with 2/4-pipe fan coil units with/without pipe sensors (24V systems only) and multi-speed PTAC units. These settings are accessed through the “I’m a Pro” setup flow. Many of the same first-run configuration steps apply as described in the “I’m a homeowner” section, however this section will callout and describe the key screens and settings.

First step is to determine the correct configuration for the application the ecobee is going to be controlling.

Fan Coil Unit (FCU) wiring on the ecobee:

4-pipe system

Y1: fan coil cooling
W1: fan coil heating
G2: medium-speed fan
G3: high-speed fan

2-pipe system

Y1: fan coil cooling/heat
W1: Aux Heat stage 1 or fan coil heat
G2: medium-speed fan
G3: high-speed fan
S1 & S2: dry contact terminals for the pipe sensor

Terminal activation for multi-speed fan control:

Fan speed selection (System Mode):

Fan speed setting is located in MAIN MENU > SYSTEM > FAN SPEED
It is a global setting, meaning that it will affect all types of fan runtime (i.e. heating, cooling, fan only, fan + ventilator, fan + humidifier, etc.)
Optimized: When running heating/cooling the fan speed will be automatically adjusted based on heating/cooling needs, the system will attempt to use the lowest fan speed while maintaining comfort.

Multi-speed setup flow options during setup process:

Fan Coil Unit, no W1 wire

Y1 detected, O/B not detected
2-pipe, no Aux Heat

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

For multi-speed options, multi-purpose thermostat terminals will be utilized.

Y2 can also be configured as G2
W2 can also be configured as G3

For the pipe sensor:

Rh becomes S1
PEK becomes S2
Low speed – G1
Medium speed – G2
High speed – G3

Main menu > Gear icon > System > Fan speed

Main menu > Fan icon

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Fan Coil Unit, w/ W1 wire

2-pipe, w/Aux Heat
4-pipe

Setting up an ecobee for dehumidification control:

This section describes how to setup an ecobee thermostat to control a standalone dehumidifier or a forced air furnace/air-handler that supports a ‘Dehum’ mode.

Select the relay state when active.

Select Dehumidifier

One wire or two wire.

After the ecobee has been configured there are a few specific settings that allow you to determine when the Dehumidifier becomes active.

To access these settings, on the device select MENU > SETTINGS > INSTALLATION SETTING > EQUIPMENT > DEHUMIDIFIER.

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

AC Overcool Max is another option to help control high humidity levels and works in conjunction with the Dehumidify setpoint under System Mode menu. This setting will allow the Air Conditioner to overcool by comparing the actual RH% vs. the desired Dehumidify setpoint.

Note: When the overcool temperature has been achieved (i.e. temperature setpoint + overcool setting), the AC system will turn off however the Dehumidifier ACC+/- relay may be still active if Dehum setpoint has not been achieved.

That is the main first time start up on your new Ecobee thermostat. In our next article we will go over more features and options that the Ecobee has to offer.

Servicing Carrier VRF Part 2

Tue, 13 Feb 2024 20:51:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Servicing Carrier VRF Part 2

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

As service and installation technicians we need to be able to figure out problems or ensure a system is running as it should. Are VRF systems serviced like a residential split system? The simple answer is no. VRF contains many more moving parts and electronics depending on what you’re looking at.

First and foremost, we need to update our resolution for our computer display to 1366×768 to ensure most of STT fits on the screen.

To do this:

Go to the Start Menu > Settings > Display > Display Resolution > 1366×768 > Keep Changes

Now the fun part……

You will find yourself on a gray screen and icons to choose from on the left column. See below for their purpose.

When you click “monitor” you’re going to get a pop-up box asking where you want the file saved. I recommend a new folder on the desktop for easy access later. Also naming the file will make finding your file easier. I personally use “SITE NAME SYSTEM NUMBER/FLOOR #/AREA”. Name it something that makes it easier for you.

The system status screen allows you to control and see a generalized overview of the system at a glance. There’s a lot of information on this screen that is very useful to you. A good tip for changing the temperature quickly is using the + or – symbols on the keyboard to change it to the desired temperature.

Refrigeration Diagram gives detailed information regarding system operations. It’s a great place to gather a large amount of information.

System Data in table view gives you status and values for everything on the system in a nice clean table. You can find the list of acronyms in the in Carrier VRF Quick Reference guide located on Partners.

Moving on to the Error Code chart we see an easy to navigate table and troubleshooting tree. Sometimes an error can just be an indicator for WHERE to look. An example of this is 0F8 (MDC Malfunction). An 0F8 means there is an error on the MDC, the primary error lies on the MDC. Find the MDC and follow the trail the system is giving.

Bear in mind that WHERE THE ERROR EXISTS IS VERY IMPORTANT! If there is an E6 on the ODU it means something totally different from an E6 on the IDU. See below how to use the error code chart to troubleshoot one version of an E6.

STT has a very vital role as a tool for both service and install. Remember patience is truly a virtue in VRF. Watch the system run and learn what’s normal and what’s not.

Next month we will cover some odd scenarios and things to look out for while a system runs. What does the Mingledorff’s Quality Assurance Technician look for? How do we find issues and correct them?

VFD Replacement on 48-50P VAV Rooftop Units

Tue, 13 Feb 2024 20:22:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

VFD Replacement on 48-50P VAV Rooftop Units

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

IYou are on a no cool service call; the unit is a 50P VAV RTU and you have diagnosis that the VFD is bad and will need to be replaced. In this article we will talk about the process of wiring and setting up the parameters for the replacement VFD.

Once you receive your new VFD, it is very important to make sure it is the correct one before going to the site. When you are on site ready to install, always practice good safety measures. Turn off power and lock it out. It is a good practice to record or take a picture of all wiring on the existing VFD before removing. Once the new VFD is installed and wired up, check all wiring.

Once you have confirmed that all wiring is correct, you are now ready to restore power to the unit. When you first plug the keypad, it prompts you for Carrier Assistance. Always choose “NO”. The drives already have a program in them. If you choose “Yes”, this will make changes to the VFD program and it will add time to the setup process.

On the P Series Units, the Comfort Link sends information to the VFD’s via the Len Bus. In most applications these units will have two VFD’s, one for the Supply Fan Motor and one for the Power Exhaust Fan Motor. Each one will have a EFB Station ID number (Supply Fan is 41 & Exhaust Fan is 42).

Now that you have the keypad plugged into the VFD you can start setting it up. On the keypad select Menu, use the arrows to select the Parameters menu. You will find the parameter index, verify and/or select correct chose using the Table below, once you made the selection, press save. In Table AB we will be using the “CARRIER DEFAULT” parameters setting.

Now that you have checked and made sure all the parameters are correct for your unit, there a few more steps. First, remove the keypad from the VFD and turn off power for 3 minutes. This will allow time for the components to power down. After time has elapsed, restore power to unit. Wait another 5 minutes before putting the keypad back into the VFD. This will allow time for the Comfort Link controller to boot up. Once that is done, press the AUTO button. The fan motor should start operating. Good job!

Sources:

HVAC Partners – 40-50 P-13T

Remember when setting the EFB Station ID number make sure the correct one is chosen!!

You are almost done, just a few parameters to check. The motor information will be needed and you will get it off the motor data plate, voltage, amps, and horsepower.

Table AA - VFD Terminal Designations

VFDwiring

Intermittent or Elusive Issues

Fri, 12 Jan 2024 19:38:00 GMT

Anthony Coker

Technical Service Manager • North Georgia

Intermittent or Elusive Issues

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

HVAC technicians often face challenges in pinpointing intermittent or elusive issues, as they can be harder to diagnose compared to consistent problems. Identifying and resolving issues related to intermittent malfunctions or sporadic performance can be more time consuming for technicians. I want to go over some of the most common intermittent malfunctions for gas furnaces that I have come across this winter, and I want to share and elusive issue I came across this past summer.

High Limit Fault

A common cause for a furnace to experience a high limit fault is restricted airflow. This can result from issues such as a dirty or clogged air filter, blocked vents, or obstructed ductwork. When air flow is restricted, heat builds up inside the furnace, triggering the high limit switch to shut off the burners to prevent overheating. Regular maintenance, including replacing air filters and ensuring proper ventilation. If the system has zoning, check to make sure all of the dampers are working properly. Take voltage readings at the zone board. I’ve see a zone board short cycle the blower motor in first and second stages. Test voltage and amp readings at the blower motor. If the system has a VFD drive, go through the parameters and make sure everything is set to the specifications to that particular motor.

Blocked vent or exhaust pipe: Obstructions, such as debris, bird’s nest, or other materials, can restrict the proper venting of combustion gases.
Faulty inducer motor: The inducer motor creates negative pressure, assisting in venting combustion gasses. If the motor is malfunctioning, it can lead to pressure switch issues.
Blocked condensate drain: in high efficiency furnaces, a blocked condensate drain can trigger pressure switch problems as it affects the proper function of the condensate removal system.
Cracked heat exchanger: A cracked heat exchanger can disrupt airflow and cause pressure irregularities, leading to a pressure switch fault.

Inducer Fan

I want share one elusive issue I came across this past summer. A homeowner had installed an air conditioning system to his fully finished garage a few years ago. The garage was professional finished with insulation and dry wall. The system worked great with no problems for years. This past summer was the first time they had any issues with it. It was now running constantly and there was sweat forming on the supply vents. I thought it could be and airflow issue or a refrigerant issue. We first checked to make sure all the ductwork was clear and free flowing, the filter was brand new, and the coil was clean. We then checked pressures, superheat, and subcooled temperatures. Everything thing was in range. We then asked the homeowner if there were any changes made to the house or the garage. It ended up that the homeowner had a large oak tree cut down and that was enough to change the load on the house.

Sometimes us HVAC technicians can’t be completely focused on just the system. When we get stumped on an issue, we need to take everything into account.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

Pressure Switch Fault

A pressure switch fault is often linked to issues with the ventilation system. The pressure switch monitors the airflow to ensure proper ventilation during the combustion process. If there is a blockage or restriction in the venting system, the pressure switch may not detect the expected airflow. Common causes of a pressure switch fault include:

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

To check the inducer fan motor in a furnace, You can follow these steps:

Visual inspection: inspect the inducer fan motor visually for any obvious signs of damage, wear or loose connections.
Electrical Testing: Use a multimeter to check the continuity of the motor windings. This helps determine if there are any electrical issues inside the motor.
Voltage Testing: Measure the voltage across the motor terminals while the furnace is running. This ensures that the motor is receiving the correct voltage.
Inspect the Fan Blades: Check fan blades for any obstructions or damage that might affect the motor’s performance.
Inducer Motor Amp Draw: Measure the amp draw of the inducer motor using a clamp meter. Compare the reading to the manufactures specifications to ensure it is within the acceptable range.
Check for binding: Ensure that the inducer spins freely without any resistance. Binding or stiffness may indicate a mechanical problem.
7.Inspect Venting System: Examine the venting system connected to the inducer motor for any obstructions that might affect airflow.
Verify Proper Sequence of Operations: Confirm the inducer motor starts and runs as part of the furnace’s normal sequence of operations.

Gas Valve

I’ve seen the gas valve cause intermittent issues. Use a manometer to check the inlet gas pressure and outlet pressure. Take pressure readings during first stage and during second stage. You can also take an Ohm reading across the terminals. Most gas valves have an Ohm rage between 20 – 40 Ohms.

Servicing Carrier VRF Part 1

Fri, 12 Jan 2024 19:17:00 GMT

Anthony Coker

Equipment Verification Technician • Southeast Region

Servicing Carrier VRF Part 1

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

You get to a school with a Carrier VRF system having issues. It’s large and intimidating. There’s an error code on the thermostat. What does it mean? How do I fix it? Scary situation if you aren’t prepared for it.

VRF isn’t so scary once you know what you’re looking for. When taking a call on the technical support line for VRF systems I commonly get asked what certain error codes are or how to diagnose an issue on a VRF system. These questions can often be diagnosed with the STT (Service Technical Tool) software supplied for free from Carrier on HVACpartners.com. Gone is the way of just a contactor and some pressure switches. With the direction technology and efficiency standards are going, HVAC systems are getting more and more electronics.

You have the software, now what? The first thing you need to know is how to hook up to the system itself. Unfortunately, these systems don’t work off Bluetooth yet. However, there are 2 different ways to hook up your computer to the system. This information is very valuable after all.

*Note that these tools may need to be ordered so it’s best to be prepared ahead of time.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

1. A MICRO USB cable. This cable is one you probably have in your trucks to charge various devices including flashlights, tablets, etc. The cable itself must be able transmit data and not just a charging cable. These can be picked up from nearly every local gas station, hardware store, or found online very easily. Cheap and easy.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

Now you are ready to start collecting the data needed.

Next newsletter we will cover how to use the software itself. What do you look for? How do I know what to do? I have an error, what does it mean? How do I correct it?

2. RS485 to USB adapter. If you’ve worked on I-Vu in the past, you probably already have one of these in your bag. This is a little more complicated to acquire than a Micro USB cable but opens your ability to attach inside the building at a Central Touchscreen communication line. These can be purchased via your favorite local HVAC supply house, Mingledorff’s.

So now we have the software and the cables.

Where do they go?

The Micro USB port is accessed behind the left front corner panel of the Outdoor Unit (ODU) at the bottom right of the spot check board.

RS485 allows you to access the system via the communication bus on X and Y on the main board of the ODU or at the Central Controller inside the building. This is valuable as you can stay inside instead of going up and down to the roof to check your computer.

RS485 is polarity sensitive. X is 1 and Y is 2.

RTU Fan Speed Setup with RTU-Open Board using Equipment Touch

Fri, 12 Jan 2024 19:09:00 GMT

Anthony Coker

Technical Service Manager • Southwest District

RTU Fan Speed Setup with RTU-Open Board using Equipment Touch

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

The Equipment Touch requires 24 vac for power (this can wired to R & C on the CTB located in the control section of unit) and two wires for communication to the RTU-Open board. See below:

There are three speed settings, Indoor Fan (IDF) Max Speed Voltage, IDF Min Speed Voltage and IDF Heat Speed Voltage. You set these settings by entering a voltage value. Higher the voltage value faster the speed of the IDF. For an example, the IDF Heat Speed Voltage is currently set at 5.5V but the Test & Balance person needs it be slowed down, you will then touch the box that has 5.5V and then the screen will let you enter a new value, if you enter 5.0 V and press done, the new entered value will be saved. The IDF will slow down.

At this time, you will decrease or increase the voltage values for all three speeds to meet airflow requirements. You will need to operate the unit in Cool Mode and Heat Mode, while in each mode you will made changes to the voltage valves as needed to meet the airflow requirements. When you are done just touch the House in the upper left-hand corner of screen to exit out. You have successfully set the up the airflow for the RTU.

Sources:

HVAC Partners-Document 11-808-652-01

You have a commercial building with multiple roof top units (48/50LC) and the Test & Balance Company is telling you they can’t adjust the air flow. The units have RTU-Open control board installed from the factory with a third-party Control Company. So, what do you do?

With an Equipment Touch (part# EQT1-4-CAR) and some 18-4 stranded thermostat wire you will be able to access the RTU-Open board and make changes to the airflow setting. Let’s get started.

You will wire C on the Equipment Touch connector to C on the CTB, wire D on the Equipment Touch connector to R on the CTB.

Wire A positive to terminal 2 on RTU-Open board Rnet port and B negative to terminal 3 on RTU-Open board Rnet port. See below:

Once you have all wiring done, power up unit. The Equipment Touch will boot up and have a display. This takes a few seconds. Once this is done, the Equipment Touch will display Standby Screen, as shown below.

Just touch the Screen to access the Home Screen.

Touch the three dots in the lower right-hand corner to access the login screen. As shown below.

Now press LOGIN and enter admin (all lower case) as the password. Then press Done to enter the configuration menus.

Once you have pressed done, the Equipment Touch will display this screen. You will then press the arrow down until you see Service Config tab.

Then you will touch the Service Config tab and it will display the screen below.

At this time, you will need to ensure that the VFD Input is set to 2-10vdc, to make a change just touch the box and highlight the correct choice. Next ensure that the Show VFD Config is set to Voltage, to make a change just touch the box and highlight the correct choice. Next touch the down arrow until you see the following on the screen

Circuit B Has No Run Hours

Thu, 14 Dec 2023 21:29:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Circuit B Has No Run Hours

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This was a call we got through our Tech Service line. This was on a 48A series unit that was about a year old.

We worked through a few items and ended up concluding making a site visit this is what we found on site.

Troubleshooting Process

On our 48/50 A and P machines they are more than just a standard package unit. In this machine, in particular, When the B circuit Started the compressor fired up but you heard an audible groan from the condenser motors. This started the troubleshooting processes

dropped a side panel on the V side of the coil to access the motors.
Used lockout Tag out process before unhooking fan motor wiring.
Verified the ohms on both fans and made sure there wasn’t a ground issue or locked-up motor.
Then worked our way to the VFD. After reinstating power, verified the VFD was getting all three legs of power in.
We tested the fans using the service test mode on the Comfort link.

This is where we found the issue two legs on the VFD were sending power. We had one leg with no power. On this job, after tacking the wiring on a 48/50 the VFD is in the cabinet behind the Condenser but the wiring then goes to the control cabinet where it splits. This is where a loose wire was the problem.

This is a great look into breaking down a problem. This issue we broken down into 3 parts: high voltage, control voltage, and mechanical. This is always a great thing to do when you’re looking at a problem. This allows you to not get overwhelmed. Breaking down the problem into these distinct sections helped in isolating and resolving the issue efficiently, demonstrating the effectiveness of a structured approach to problem-solving.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

Puron Advance Refrigerant 454b – Q&A

Thu, 14 Dec 2023 19:44:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Puron Advance Refrigerant 454b – Q&A

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

In this newsletter we will cover a few key topics that will explain a few details pertaining to the use of R 454b. We will continue to cover more details in future newsletters. This briefing will give a few important and updated details to prepare you for the change in refrigerants.

Safety is of main concern with the A2L refrigerants. A few things are still up in the air, under research and could change as new information becomes available. We now know that Carrier/Bryant equipment up to 25 tons will have R 454b. This includes ductless and VRF at the current printing of this newsletter.

Servicing

Charging/servicing techniques will remain the same when switching from Puron to Puron Advance as they are both low glide blends. Charge limits are based on the home’s square footage and other design criteria. The equipment should be properly leak checked and should be evacuated and purged before any brazing.

Cylinder differentiation

The refrigerant 454b system’s cylinders color will be a light green gray. The A2L refrigerant cylinders will have a red top for identification, to warn that it contains a mildly flammable substance. The cylinders for A2L refrigerant drums will have left-handed threads.

The cylinders for the A2L refrigerants will feature a pressure relief valve instead of a rupture disc, for increased safety. A relief valve will only release content until the pressure setting allows the valve to close. Also, the technician will not lose the entire drum of refrigerant should it be released. The technician can continue to use the remaining refrigerant until the drum is emptied. The disposal procedures have changed also. For A2L cylinders, a non-sparking piercing tool, like a brass punch, must be use to puncture the side of the cylinder before disposal.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

The recover cylinder is gray in color with a yellow top. A2L cylinder will have a red band as well as left-handed threads. And as always, keep a refrigerant type clearly identified and do not mix refrigerants.

Ignition

Most A2L refrigerants are so mildly flammable that there must be a direct flame source and a high concentration of refrigerant to create a flame. If and A2L refrigerant were to ignite, the flame would be unsustainable. An A2L refrigerant flame would spread at an extremely slow speed, less than half a mile per hour. You can walk faster than that. Most A2L refrigerants are difficult to ignite, because they have a high MIE or minimum ignition energy. Many common household items like a cordless drill, toaster, hair dryer, or electric heater will not ignite A2Ls. They require higher concentration levels to achieve a flammable mixture.

Tools and Equipment

So what type of tools will be needed to work with Puron Advance? We now know for sure you will need a left-handed thread adaptor for your refrigerant drum. Some tool manufactures are now selling left-handed hoses charging hoses that will help with this issue. Well, it requires the use of hand tools and equipment with no spark and no ark. Make sure all the tools that you are purchasing are UL certified. Your current gauges, digital or analog and hoses used with 454b can be the same as used today, however, a dedicated set should be used the same as when working on R454b and 410a to avoid cross contamination. Check with the manufacturer to make sure equipment is rated for use with R 454b. 454b cylinders will have a red top and the hose connection will be reverse threaded or left-handed threads. As always, before beginning work, make sure equipment is properly grounded.

Now we’ll talk about some primary concerns with equipment containing slightly flammable refrigerants. One of the primary concerns is refrigerants ignition of a refrigerant leak during equipment operation, the potential for refrigerant ignition during equipment service, and a refrigerant release during a structural fire. As always as mentioned above, a few things are still up in the air and could change as information becomes available. One thing is for sure, you will need to have a fire extinguisher always rated Class B for a chemical fire available.

The primary areas of concern of oxygen displacement are the release during transit in a service vehicle. Catastrophic leak into a confined space during service are also an issue.

Indoor unit

There will be several component changes from the standard 410a systems. Indoor Equipment Indoor equipment will require an active dissipation board and refrigerant sensor. In other words, if refrigerant is present then equipment operation will be interrupted and the indoor fan will be energized to keep refrigerant below its lower flammability level dissipating refrigerant. It will also have an updated wiring diagram. The TXV will be designed for R 454b. New safety labels will be apparent throughout the indoor equipment. The evaporator coils will have straight liquid and vapor lines on all tier to allow brazing or press or mechanical fitting use. The liquid and vapor lines will be extended longer to allow for these changes as needed for your installation.

Outdoor unit

On the outdoor unit, the new compressor will be designed for R454b. It will also have a new A2L design contactor. The new A2L contactor will have a top cover with a small hole to access push button. There will be minimal air gaps inside the contactor to act as a flame arrestor. There will be wire sleeves on the high voltage wiring on the compressor. The compressors will have enclosed molded plugs and provide the necessary isolation from ignition. Wire sleeves will be installed on the compressor and crankcase heater wiring to mitigate potential ignition points. Pinch points are carefully assessed at the factory. It also will be having new safety labels throughout the outdoor system. Straight service valves on all tiers to allow brazing or press fitting use also. Red caps will signify the new R 454b and also installed to alert installers of something different.

Changes in the Installation

Yes, there will also be some changes. There will be several new installation practices needed. We need to make sure the disconnect box is not mounted on the unit.

On the indoor unit, the sensor comes factory installed for vertical orientation, the location will be clearly identified for other applications. You will need to connect Y/Y1 from the mitigation board to the thermostat connections. For furnaces only you will mount the mitigation board to the side of wall of the furnace. Connect G from mitigation board to furnace control board. Connect 24 v power to mitigation board. Use the mitigation board self-test button to test the connection.

There will be a 10 second sensor warm up delay. Thee will be a self-test button with a 60 second mode. It will have a green LED for normal operation, and a red LED for mitigation mode. Safety chain interrupts Y/Y1. The blower stays on for 5 minutes after the sensor readings are below mitigation. Sensor over temp sends unit in mitigation mode. This allows heat pump heating or colling call after 15 minutes of mitigation. The blower is always on in this mode.

It is also well noted that Carrier/Bryant approved electric heaters are not considered an ignition source.

Pressures

We covered pressures in past newsletters, but it is necessary to bring this subject up again while we are communicating with new techs in this artilcle about R 454b. Let’s compare operating pressure vs. saturated temperatures. If we have a saturated suction temperature of 40-degree Fahrenheit. The suction pressure of R 410a equals 118.8. With R 454b, the suction pressure will be 113.3. If we have a saturated condensing temperature of 110 degree Fahrenheit, the condensing pressure of R 410a will be 366.4 psig. The R 454b will be 349 psig. So these pressures are definitely not the same, but a small difference.

There is much more information forthcoming relating to R-454b. We are on scratching the surface. Stay tuned for much more in future newsletters.

Sources:

Carrier Literature presented at Outlaw Conference
The NEWS: An HVAC Technicians Guide to R-454b
HVAC Partners.com

Universal PBA Inverter for 9 and 12K Btu Outdoor DLS

Thu, 14 Dec 2023 19:14:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

Universal PBA Inverter for 9 and 12K Btu Outdoor DLS

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Historically, any dipswitch on a Carrier/Bryant mini split outdoor PC board were set by the factory and left alone. Now, for many of the outdoor units there are universal replacements. This PBA (Primary Board Assembly) Inverter will cover almost the entire ensemble of Carrier/Bryant ductless 9,000 and 12,000 Btu heat pumps and air conditioners. It makes a difference how you set the dipswitches

What is your compressor model number? Finding this out can be easy or hard.

I vote easy! Use your handy dandy service tech app. Any version will do…

Tips and tricks:

Take photos or good mental notes of the CN#(s) on each connector.

Some connectors can fit in places they don’t belong. However, they are color for color.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

What type of fan motor do you have?

A DC fan motor will have only 3 wires and no capacitor. An AC motor will have 5 wires (3 to the motor and 2 to the capacitor). The universal PBA comes with an adapter plug and new capacitor for AC voltage motors. The plug locations on the board are specific to each motor. There are 2 dipswitches labeled SW2 for whichever one you have. In North America: for DC fan motors, both bit 1 and 2 should be off. For AC both bits should be on.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

Everything else should be plug and play!

Part Number: 17222000A59952

Features of the new PBA Inverter

Capacity: 9-12K Btu
Power supply: 220V-240V, 1Ph, 50 or 60 Hz
Fan type: DC motor or AC motor
With or without electronic expansion valve
11 different types of compressors

Find the service literature for your specific outdoor unit. The compressor model numbers, and ohm values are published in every service manual for these units. Match your numbers to the chart provided on the back of the PBA and table below.

Or, if you prefer the hard way, just check the numbers on the compressor. Unfortunately, the model tags are facing the inside of the unit. You can try to get your camera phone in there and get a photo or use your mirror from your torch set and a flashlight to see back there and verify the model. Then set the SW1 dipswitches accordingly. See table below.

The Building is Hot, and I Need My Chiller Back Online

Wed, 15 Nov 2023 14:59:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

The Building is Hot, and I Need My Chiller Back Online

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This is not a fun phrase to hear when you talk to the customer on-site. It gets worse when you open the panel door and see the Comfort link panel flashing. This can be a touch overwhelming but let’s drive forward into the problems and see what the machine is doing.

The Comfort link board shows codes T134, T113 and T093. The First Code is Circuit B Low Suction Pressure. This code will show if the suction pressure on the circuit is below 23 psiq. The Second Code Circuit B loss of Charge, This code will show if the Suction and Discharge pressures are under 26 psig. The Final Code is Circuit B Suction Pressure Transducer Failure, This code comes on when the suction pressure is outside of the range. Looking at the codes it’s very clear after putting gauges on the circuit to confirm there is no gas in circuit B. This will be the method of getting A circuit back online.

Procedures for getting the chiller back online

Turn the SW1 switch to the center position. This allows the MBB to take the commands without having a moment of issue.
Go to the configuration menu on the Comfort link. Then go down to the SERV
Select enter and go down to EN.B1 and disable the remaining B circuit Compressors depending on the size of the chiller.
Take the Suction pressure transducer off the pipe. It is located next to the B1 compressor.
Take the Circuit B Discharge Transducer off the pipe it is located behind the compressors on the Discharge header.
Using your Gauges Thread the Suction transducer on the low side line. Then thread the discharge to the high side of your gauges. Using a refrigerant gives the 2 transducers about 145 PSIG.

Once Completed go into the alarm menu to reset the alarms. This will allow the machine to run on A Circuit when B is down. This is a great tip when you run into a jam on this particular style chiller to get supplement cooling back into the space

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

Puron Advance – 454B

Wed, 15 Nov 2023 14:50:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Puron Advance – 454B

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

We have mentioned Puron Advance or 454b in our Fall Service Updates and in past newsletters. This newsletter will be more information about this refrigerant. So just what is Puron Advance? Puron Advance is Bryant/Carrier’s solution refrigerant for meeting the EPAs anticipated global warming potential (GWP) limits for refrigerants and the scheduled phasedown of higher GWP refrigerants like Puron (please do not get Puron which is refrigerant 410a confused with Puron Advance which is refrigerant 454b). It is this refrigerant we will be transitioning to for our ducted and ductless residential and light commercial products. We plan to start this transition in late 2023 to be ready for the 2025 deadline. The EPA, or Environmental Protection Agency, is implementing a phasedown of existing higher GWP refrigerants, including Puron. All of you remember the R 22 phase out and how the supply issues and hefty price increases caused havoc for a while during the phase down period. This transition will not be anything like the previous transition.

So why the big explanations? Because this is the refrigerant that Carrier and Bryant products have selected for the immediate future. Also, 80 % of the industry is also using R 454b. Puron Advance performs very well in normal and high ambient conditions. It also has similar operating temperatures, pressures, and oil compatibility to Puron, meaning technicians will have less of a learning curve compared to the alternative. Please remember as mentioned earlier, this transition will not be anything like the transition from R-22 to R- 410a.

AIM Act Impact: Transitioning Away from R-410a Towards Puron Advance (454b)

The EPA, or Environmental Protection Agency, has passed the AIM Act, or American Innovation and Manufacturing Act, in which the phase down of the supply of R 410a refrigerant will total 40 % starting in 2024, along with other amendments. This reduction in production of 40% of R410a is of great concern to our industry.

Also, by January 1, 2025, R- 410a, will no longer be allowed in newly manufactured residential and rooftop light commercial HVAC products. Also, of great importance, please note that as of January 1, 2025, HVAC equipment manufacturers will not be allowed to build equipment using the current R-410a refrigerant.

So, with all this legislation taking place, Carrier/Bryant Products has been working towards creating a more GWP friendly refrigerant for over 10 years. Now, after years of research, development and with products currently in field trials, we anticipate beginning to start the transition to Puron Advance in late 2023. With the 40 % reduction in 410A in 2024, we will probably see price increases in this refrigerant beginning in January 2024. Below is the chart of anticipation of production of equipment in the next 3 years of refrigerant 454b

Preparation for Transition: Resources and Updates for the Shift to Refrigerant 454b

So, let’s get ready and get ourselves prepared, our customers prepared, get all of our technicians prepared, and when the transition takes place, it won’t be new information. Much of this information is also printed in HVAC Partners. This information is also talked about on our podcast by Jenny Brown and Deanna Lassiter entitled “Caffeine and Coils”. Much of this information is in our newest website, heatcool.com. As mentioned earlier, all technical service managers include much of this information in our Fall 2023 service updates. In the next newsletter, we will get all prepared with what we now know and include the changes since the first newsletter when we introduced refrigerant 454b. But remember, change is inevitable, and even new information could change with continued R and D, or research and development as we use new products.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

Communication is Key – Pt. 2

Wed, 15 Nov 2023 14:37:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

Communication is Key – Pt. 2

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

What exactly does no communication mean regarding Infinity and Evolution equipment? No communication means there is no clear signal of information received by the UI (User Interface), or it has been interrupted.

When no communication faults occur, there is a process that simplifies diagnosing the issue. Always start with the basics. Loose control wires in wire nut connections, ABCD plugs or UIs not seated perfectly, and crowded terminals can cause issues in a communicating system. Control wires running alongside or across high voltage wires can receive interference from the EM (electromagnetic) field generated by the current (amperage) from the power wires. Generally, control wires should be kept away from high voltage wires. If this is unavoidable, it is recommended to use a shielded stranded cable for the AB circuit and ground the cable on one end. Issues from interference are uncommon, but should be considered during the diagnosis.

Look for signs of moisture, especially inside of horizontal fancoils. Dirty power from wet electrical connections, as well as water damage to transformers and PC boards can cause poor communication or false codes to be generated. Many horizontal right fancoils are installed with high voltage wires entering directly above the control board. When this penetration is not sealed, there is potential for hot and/or humid air to mix with cool air inside the cabinet. This can be a source of intermittent fault codes as water condenses and drips down onto the board, then runs off and the code clears.

For all Infinity and Evolution model FE 002, 005, and 006 fancoils installed horizontal right, it is imperative to correctly “flip” the air seal assembly at the top of the coil, and relocate the drain pan support bracket to its proper location. Either of these two items missed or done incorrectly will eventually make for a water filled cabinet with completely saturated insulation. This results in an extremely wet environment inside the fancoil and will wreak havoc on all internal electrical components. Also, it can cause the exterior of the cabinet to sweat, which has its own set of issues.

Tips and tricks:

Once a cabinet is soaked, it is easy to diagnose these problems as resulting from a clogged drain line, leading to the wrong repair, and then a callback. This can happen to all Carrier, Bryant, or WeatherMaker fancoil models with an “A” coil. See below forsnippets from the installation manual and photos of the support bracket.

Tips and tricks:

Communication is active when the UI is connected. Disconnect the UI to put the circuit at rest. It may be easier to identify what component is the issue with communication at rest versus fluctuating.

A resting voltage of 3.2 VDC or less on a system is the borderline of no communication. Comm voltage being dragged down can cause all sorts of intermittent issues, such as touchscreen UI’s becoming non-responsive, or momentary fault codes to be generated. Similar to checking ohms across the control wire, its integrity can also be checked by measuring resting VDC at the components and at the other end of the wire. A small drop of voltage of less than 1 VDC is acceptable across long lengths. If a drop of more than 1 VDC is found, the wire is likely compromised and pulling a new wire is recommended.

When a Carrier Infinity or Bryant Evolution system is communicating across all components, the VDC is constantly fluctuating. A range between .8-4.5 VDC may be seen on your digital meter in momentary flashes. An analog meter will show this as a bouncing of the needle. If problem components or wires are dragging down the communication, it can go into the millivolt range. When 24 VAC loads – such as contactor coils, gas valve solenoids, or heat relay coils – are engaged on a system running with low comm voltage, it can be the “straw that broke the camel’s back”. When these loads engage it can cause momentary no communication faults to occur, followed by the system dropping out, and then, the cycle repeats as everything comes back online. One must be methodical to find the issue. While measuring comm volts, begin a process of elimination.

The following is a real-life example from the field:

A 24 SEER heat pump system with two zones has a recurring indoor communication fault which always happens on the coldest nights. It is determined the event occurs shortly after the system engages heat strips due to going through a defrost cycle. Properly made connections, and ohm values of each component are confirmed to be good. However, comm volts are fluctuating in the millivolt range.

The process of elimination with power applied and communication active is started at the fancoil PC board. First, the blower communication wire is unplugged from the board, but the low comm remains. Next, the blower is plugged back in, and the tstat wire from the fancoil to the zone damper control and smart sensor is disconnected, but the low comm still remains. The zoning is reconnected, and then the outdoor unit wire is disconnected. Immediately, the comm volts return to normal, and the issue is isolated to the outdoor unit. The wire to the outdoor is reconnected at the fancoil. This wire had already been verified to be good, but to verify again, the AB plug is disconnected from the outdoor PCM. Comm volts return to normal and the control wire is eliminated as the problem, leaving only the heat pump as the source of the issue.

Instinct would be to condemn the outdoor PCM. However, there are three different communicating components in the outdoor unit: the PCM, the Bluetooth module, and the VFD. The AB plug is connected back to the PCM. The VFD comm wire is disconnected, but the low voltage remains. The VFD is connected back and then the Bluetooth module is disconnected from the PCM. The comm volts return to normal, and thus the Bluetooth module is identified as the source of the problem. A new Bluetooth module is installed and updated through the Carrier Service Tech app, which should be done every time a component is replaced on 24/26 SEER units. The system is put through a full reinstallation at the UI (which should be done every time a communicating component is replaced). The system is checked out first in heat strip mode, and then in heat mode with a forced defrost to verify it is working properly. Finally, all functions of the rest of the system are checked and found to be good.

Learning these methods and how to use this knowledge is key to being efficient at diagnosing Infinity and Evolution communication problems. Hopefully, this article has helped you have better understanding when it comes time to diagnosing various communication issues you may encounter in the field.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

If inside the cabinet is dry, then verify all connections are good. Redo any crowded plug or terminal by making a pigtail in the control wire. It is recommended to only have one wire under each terminal. Another thing to look for is improperly stripped wires that are scored too deeply by wire strippers. If poor installation practices are suspected at all, then do yourself a favor and remake all connections.

Remove horizontal drain pan support bracket from coil support rail on left side of unit and reinstall on coil support rail on right side of unit.

Once you have verified that all wires and connections are good, it is time to take the next step in diagnosis. Know your ohm values. Each communicating component has a specific ohm resistance range at their comm bus. Please see the chart at the end of this article for up-to-date ohm values. If all components read correctly, then the control wire(s) could be the issue. Read from the other end of the control wires and ohm through them back to each component. Any difference from your original readings indicates a flaw in the wire.

If all these possibilities have been eliminated, then advanced diagnosis is all that remains. Most Infinity and Evolution PC boards with power applied have a resting voltage of approximately 4.5-4.6 VDC on the AB pins. Specific exceptions to this rule are the early generation and current versions of 18 and 19 SEER five speed AOC boards, which have a resting 2.8 VDC, and can be identified by a lower 16-19K ohm value at the comm bus. AOC produced between December 2014 and early 2022 ohm between 28-32K and will have a resting 4.5-4.6 VDC.

Customer States the Unit Won’t Start

Fri, 20 Oct 2023 12:50:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Customer States the Unit Won’t Start

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

This phrase can be an assortment of items on our 48TC package units. After the inspection of the unit, you see the charge is okay, No broken belts and all main voltage is present. Now after bumping the contactors, it shows everything is operational. It is determined we have an electrical issue which for most technicians not a strong suit.

We are talking today on our electrical mechanical board shown below. Once you know the inside working, this board is very easy to master. The First step after verifying you have a call for cooling. The unit runs through the unit shutdowns. These are on the right side of the board they consist of the Smole and Remote shutdowns. If those are good, then it will send power through plug 1 on the Econ plug. Then it comes back through at 2 on the Econ plug. This is a 24-volt signal. Once verified there it goes to jumpers 6 and 7 if there is no reheat on the machine. If it is present runs through terminals 5 and 6 on single compressor units. Terminals 7 and 8 for dual compressor units. Once it passes through it will start the fan. This will then go from terminal 6 goes into terminal 4 on the compressor plug. This runs through the high and low-pressure safety. Once cleared there it goes out terminal 6 to the fan-providing switch mounted on the squirrel cage of the blower. This is closed the compressor will start.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

With the knowledge now of this board. When you run into a unit not working the wiring schematic will not be as daunting to negotiate. This style control is the most common you run into on the 48tc units. But this is also a common board in multiple carrier package units ranging from 3 tons to 20 tons.

EPA 608-Tips for Passing the Exam

Thu, 19 Oct 2023 18:19:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

EPA 608-Tips for Passing the Exam

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

So, you want to take the EPA exam. We have had many techs take the exam this past year. We offer this exam primarily as an on-line class with the tech using their laptop with a camera. We originate the class thru the zoom format. We’ll normally send the tech a couple of correspondence emails to ensure we have the correct email address to send the web address to sign in on class day. The tech can take the class and exam at the office or at their residence. They will need internet to log in to the class.

Test Requirements

Some questions have been asked by many techs and service managers. Why can’t my tech use his phone or tablet? Well, this is a very good question. We have had some techs to use their phone to view the review of the class, but problems with this sometimes occur. The tech’s phone has lost battery power usually while they are taking the test. Once the test is lost, many times the tech will need to retake the entire exam. Also, not everyone can see and hear on their cell phone or tablet as well as a laptop. Many times there is not a camera on the phone or tablet for us to view the techs. We need to record the techs during the exam to ensure the credibility of the exam. We do not recommend using a cell phone or tablet – please make sure each tech has access to a laptop with a camera.

Preparing for the Test

If you or your techs are going to take the EPA 608 review and exam, we can offer several preparation tips. Once your tech is signed up, our personnel send the tech study material to the email address that is given. It is very important for the tech to read and review the study material sent to the email address. So, a bit of advice. Please keep in touch with the tech to ensure he indeed does receive the study material as well as information leading the tech to the ESCO home page and directions to the practice study questions for all four areas of the EPA 608 which include core, type 1, type 2, and type 3. We have asked many techs who earned their Universal card, what was their preparation? Each without fail stated they studied the material we sent them, and listened closely to the presentation.

Receiving your EPA card

One clear advantage of taking the EPA 608 on-line is you get your results immediately. The tech will receive their EPA card in a week to 10 business days. Once the tech receives their card, they need to make a copy and get both laminated. We advise storing the original card in a safe place. By getting your cards laminated, the tech can ensure moisture won’t deteriorate the card. Also, should you lose your card, make another copy of your original card.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

What if a technician doesn't pass?

So, the tech didn’t pass all sections, how does this work? The tech must pass core to get any certifications. If the tech passed core and type 1 only, they would receive a type 1 certification. If the tech passes core and type 2, they will receive a type 2 certification. If the tech passes all sections, core, type 1, type 2, and type 3, they will receive a Universal Card. We urge all techs to study hard to earn their Universal card.

Also, unless the tech misuses their card and is investigated and charged a violation by the EPA, the card is a lifetime card. They never have to get their card renewed. It is the techs responsibility to keep up with the trade and the different refrigerants and equipment introduced in the HVACR industry.

A2L refrigerant updates

The EPA 608 preparation class materials and certification were updated a few years ago to include the new A2L, flammable and slightly flammable refrigerants. This information is subject to change with innovations in the HVACR industry. So, it is the technician’s responsibility to keep up with the HVACR industry. We at Mingledorff’s offer Fall and Spring Updates each year and a monthly newsletter to keep the contractors, technicians, and all affiliated with the trade, updated as much as possible. Keep in mind though we cannot in anyway have all the information that is needed during these updates. The technicians need to constantly keep in touch with their equipment manufacturers, salesman, read current periodicals, and search equipment websites to stay up to date with the HVACR trade.

Now that you have read and understand how to receive your EPA 608 Universal card, lets get to it. Start studying and get that Universal card.

Communication is Key – Pt. 1

Thu, 19 Oct 2023 17:55:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

Communication is Key – Pt. 1

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

When I first learned about Carrier Infinity and Bryant Evolution systems, the idea of communication seemed like such a foreign concept from what I had been taught. It added a new element to troubleshooting that I had not learned in all my previous experience working on basic controls in mostly residential and light commercial applications. Carrier and Bryant communicating systems are different from all of it. Every control component has a voice, speaking a programmed language of binary ones and zeros, working in concert for the common goal of ideal comfort and full customization of the environment for the user, while always providing superior energy efficiency.

When I explained this to homeowners, I compared it to a perpetual boardroom meeting. The User Interface is the chair, taking in all the information from the inside and outside directors, interpreting the data, and ensuring that the meeting always runs smoothly. This analogy also works well when there are communication issues. For example, if one of the directors starts yelling or speaking nonsense, then the chair cannot hear what the other directors have to say. Resolving the issue means diagnosing what went wrong and how to re-establish good communication across the board.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

This information is lost if these boards are replaced. Fancoils boards do not have model plugs and require set up of the correct model during the re-installation at the UI, which must be done every time a communicating component is replaced throughout the system.

Look out for “Communication Is Key – Part 2” in next month’s newsletter where we will take this knowledge and focus on troubleshooting communication problems when they arise. In the meantime, check out our archives link below for the article by Jonathon Pullen titled: “What We Have is a Failure to Communicate”.

The main controls that require the AB communication wiring are the UI, the indoor furnace or fancoil, and the outdoor unit. Zone Damper Control Modules also require ABCD wiring, as well as Smart Sensor zone controls. Fancoil and furnace control boards communicate with the variable speed ECM (Electronically Commutated Motor) blower motors and provide RPM and static pressure data to the UI. If smart heat strips are used then the KW output is identified by the fancoil boards by way of a unique resistor, read by the UI through the indoor board. If basic heat strips are used, they must be identified at the time of installation.

Early generations 16, 19, and 21 SEER two speed unit control boards required power from the indoor transformer, using AB and CD connections, and communicated measured inputs, such as outdoor temperature, liquid line coil

temperature, and line voltage, to the UI. Later generation 16 and 19 SEER two speed units added a transformer and omitted CD from their control wiring.

Tips and tricks:

All legacy user interface UID01 models A-D, and Z (for zoning) were compatible with any communicating 1 or 2 stage equipment. All touchscreen models are backwards compatible to all Infinity and Evolution equipment.

The Carrier Infinity GREENSPEED and Bryant Evolution EXTREME 20 SEER units were the first to have true variable speed compressors with a range from 40% capacity to 100% using a VFD (Variable Frequency Drive) inverter board. These VFDs take high voltage single phase power and invert it to three phase DC, then invert it again to three phase AC power (with the bottom half of the sine wave cut off). The variable speed is achieved by adjusting the hertz to the compressor. They use a basic 24 VAC transformer for power to the control board instead of being powered by the inverter, and only require AB wiring for communication to the UI. They communicate with the inverter board and have the same inputs as the 18 and 19 SEER units.

Tips and tricks:

The UID01 control model V was the only legacy version that had the capability to drive a 20 SEER variable speed unit. All touchscreen UI models A-C are compatible.

The heart and mind of all communication is the User Interface, nicknamed the UI. It is a smart TSTAT, which means that not only is it programmable, but it also learns the requirements of the user over time, and how to achieve this in the most efficient manner possible. It does this by monitoring outdoor ambient temperatures and indoor humidity to know how fast it needs to run the system to achieve the homeowner’s desired setpoints.

The basis of all Carrier and Bryant communication is the control wiring. Kept simple, they are ABCD. Terminals A (green) and B (yellow) provide a circuit for communication, while C (white) and D (red) are the 24VAC common and power respectively. In early generation equipment one transformer located at the indoor furnace or fancoil provided power to all controls in the system. Modern versions utilize transformers at the indoor and outdoor equipment. The indoor unit provides power to the UI, any zoning controls, and possibly a NIM (Network Interface Module), when required.

A Network Interface Module is used as an intermediary control. Infinity and Evolution fancoil control boards do not have a Y2 terminal on the analog control lugs, therefore a NIM is required when using a non-communicating two stage outdoor unit. Furnaces do have a Y2 terminal, so they do not require a NIM. It is necessary to use a NIM when connecting basic Infinity and Evolution systems to an ERV (Energy Recovery Ventilator). A NIM is not required for an ERV if the system is zoned, as the zone Damper Control Module has a connection built in.

The 18/19 SEER five speed outdoor AOC (Application Operational Control) is powered from and communicates with the MOC (Motor Operational Control), nicknamed the inverter. These MOC boards take high voltage single phase AC power and invert it to three phase DC, which drives the condenser fan motor and uses PWM (Pulse Width Modulation) to gently change between stages in the 5 speed compressor. The MOC monitors temperature, current, status of the compressor, outdoor fan, and the inverter and communicates this to the AOC, which then sends all the information to the UI. These units have the same outdoor ambient, liquid line coil, and line voltage measurements as the 16-21 SEER two speed units, but have added discharge temperature, suction temperature, and suction pressure. The capacity for each model ranges from 25% in 1st stage to 100% in 5th stage.

Tips and tricks:

There are no legacy Controllers that will work on the 5 speed equipment. The touchscreen UI model A had to be at least version 11 to work with these units, and version 12 was required for the 13000 btu unit. All touchscreen UI models B or C are compatible.

Tips and tricks:

Touchscreen model B controllers must be version 3.0 firmware or higher to drive these units. All model C controllers are compatible.

The most current 24/26 SEER GREENSPEED and EXTREME units work much the same as the first generation, except for a few upgrades. They now have a capacity range from 25% to 100% and have added a discharge pressure measurement to the ensemble for more protection and adjustment ability. Also, they provide a basic 24 VAC transformer for power to the control board and have added a communicating Bluetooth Module for the purpose of monitoring and updating the unit components through a phone app. Updating is required at the time of system commissioning and during any service or maintenance to ensure the unit is working at peak ability. It is imperative that all technicians have the Carrier Service Tech App, which is an extension of HVAC Partners, so they can connect to these units via Bluetooth for monitoring performance and updating.

All outdoor units and furnaces have a model plug, also known as a personality plug, which identifies the unit and tonnage to the UI. Model plugs consist of two resistors of varying ohm values to provide a unique identification. The original control boards on all outdoor units, furnaces, and fancoil boards have their model and serial numbers burned into them at the factory.

NIMs – Network Interface Module

Thu, 14 Sep 2023 10:40:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

NIMs – Network Interface Module

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Recently we have been getting calls from techs about NIMS installations. One caller recently said he had an infinity system with an “infinity” water source heat pump with a no cool call (as told by the homeowner to the tech). The infinity interface was giving a 179 code, or no communicating with the outdoor unit.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

He then found the NIMS installation with a geothermal heat pump. “The infinity” geothermal heat pump is what he was told by the homeowner. But in reality, it was a geothermal heat pump communicating by use of the NIMS installation

He was ohming out the NIMS module. We suggested that he try running new thermostat wire, or using 2 extra wires in the bundle not being used. Once he made the changes to the wires on the NIMS and the indoor infinity furnace, guess what. The code 179 went away. The geothermal heat pump then began operating. Communication was established. So thus, it was not communicating with the older thermostat wires, but operated and communicated with the indoor infinity furnace and UI with the newer thermostat wires.

So, the NIMs installations is definitely a tool all techs could use if needed on certain installations. The Network Interface Module (NIM) is used to interface the following devices to the Infinity ABCD bus so they can be controlled by the Infinity System. The following devices do not have communication ability and the NIM is required to control: • A Heat Recovery Ventilator / Energy Recovery Ventilator (HRV/ERV) (when zoning is not applied). • A non-communicating single-speed heat pump with Infinity furnace (dual fuel application only). • A non-communicating two-speed outdoor unit (R-22 Series-A unit)

More information on the NIMS can be found in HVAC Partners, or on your Carrier or Bryant service app.

So what have we learned from this article?

What is a NIMS? A Network Interface Module
Some equipment can be operated similar to an infinity/evolution system with the installation of a NIMS
Always listen to your customer, and check out all components of the service call before making a repair attempt (could save you a lot of time)
The NIMS must be installed out of the weather.
The full installation of the NIMS application can be found in HVAC partners or the Carrier/Bryant service app

This installation was on a 4-story home, and the tech had not yet gone to the basement to troubleshoot the “infinity” water source heat pump, as he was told he by the homeowner. He was in the attic at the infinity furnace above the 4th floor. He was getting his dcv in the proper range on his A and B green plug on the air handler, 3 to 4 vdc. His indoor board ohm reading was in range, 28k to 32 k. The tech ohmed out the A and B thermostat wires on the water source heat pump from the upstairs. His ohm reading was not in range of a normal infinity board. His reading was around 64.4k. The tech then made the long walk to the basement where the “geothermal heat pump” was located. Bingo.

The Compressor is Not Starting

Thu, 14 Sep 2023 10:35:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

The Compressor is Not Starting

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

With technology advancing more and more every day, the days of relays to contactor style control are behind us. Carrier units with MBB boards have sensors everywhere from the suction pressor to Current sensors on the compressor. This does have a great benefit to having a unit in which you can attach one set of remote contacts then it will run. But this can cause issues once you start getting wear on the sensors. This can cause the codes P.16-P.27 which can cause massive headaches to hunt down.

The Code states the Compressor has not started or pressure has not been established. This Fault is read if the compressor discharge-suction did not increase 10 psig in 2 min. This goes back to the sequence of operation for the starting of the compressor. The sensor that makes a technician’s job easier on checking trails is also how the machine knows it’s doing what the MBB commands. This can affect the unit not being able to run at full capacity to shutting down whole circuits. This can come from faulty transducers to faulty current sensors. This will make the MBB Board think the compressor is not operating correctly

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

The potential fixes for this are very simple if you take it step by step. The first step is to verify the standing pressure. Use a set of gauges tied in the service ports next to the transducer. Once the gauges are installed use the Comfort Link to verify the pressures of the Gauges. If they are off more than 10 psi the bad transducer needs to be changed. If the transducer’s reading is good verify the control voltage to the contactors and make sure there is no loss going to the contactors from the MBB. Make sure you have the signal out of the scroll protection module. If those are present and the transducer is fixed the problem is solved.

Using Bluetooth on 24/26 SEER Carrier Equipment

Wed, 13 Sep 2023 16:40:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

Using Bluetooth on 24/26 SEER Carrier Equipment

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

The most current 24 and 26 SEER Carrier GREENSPEED and Bryant EXTREME offer a few upgrades from the original versions. Now, they have a capacity range from 25% to 100% and added a discharge pressure transducer to the ensemble of inputs for more protection and adjustment ability. Similar to the original Greenspeed and Extreme units, they provide a basic 24VAC transformer for power to the primary control module (PCM). Another upgrade is a communicating Bluetooth Module for monitoring performance and updating the components through the Carrier, Bryant, or Replacement Components Service Tech Apps. It is highly recommended to perform this update at the time of system commissioning and later during any service or maintenance performed to the equipment.

What is Bluetooth?

Bluetooth is a wireless technology used to exchange data between devices over short distances, mainly as an alternative to wired connections. It utilizes UHF radio waves with low transmission power, covering a max distance of about 33 feet.

What Apps Can I Use?

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

“Firmware” will search and show current and latest versions for each component.

The System page is a very useful tool to have for working on these machines. No gauges or meters are necessary until you find the need to fact check the information. All input and operational values are displayed here in one cohesive list. In the “Refrigeration System Info” we find compressor and outdoor fan RPMs; outdoor coil and ambient temperatures; suction pressure, temperature, and superheat; discharge pressure, temperature, and superheat; the heating EXV (Electronic Expansion Valve) position, and the vapor injection EXV position (only used on the 5 ton models). In the “Inverter Info”, we find line voltage; AC line current (amp draw); DC bus voltage; PFCM (power factor correction module) temperature of the reactor circuit(s); IPM (inverter) temperature. In the “Operational Status”, we see heat pump mode percentage (demand); a lockout timer counter; low ambient cooling on (if it has been enabled in the UI setup); and curtailment.

Curtailment is for when your utility requires a way to interrupt the operation of the unit during peak periods. The UTIL connections must be wired to a normally open set of contacts. When the power utility sends a signal to close the contacts, a curtailment indication can be seen on the Bluetooth app and the Infinity or Evolution Control (UI), and the system will be commanded to shut down.

Hopefully, this article has helped you understand how to use one of the three available Service Tech Apps for connecting with Bluetooth on the 24 and 26 SEER equipment. Stay tuned for next months article, “Communication Is Key – Part 1”, where we will discuss Infinity and Evolution equipment through the years, and provide some insight into the changes as the technology of these systems continues to advance.

Be aware that signing in as a guest will only give you limited ability with the apps.

Once signed into your account, touch “Connect to Outdoor Unit or Furnace”. This will take you to the “Connect to Equipment” screen. Select “Outdoor Unit (Bluetooth)” and the app will search for equipment.

If no equipment is found, you may need to resync your device.

Verify the Bluetooth Module has a red LED.

If any of the details seem suspect, then further investigation is necessary. As these units can change how they operate based on inputs, the information being correct is critical. Use your gauges and meter to compare and contrast versus the data. Compressor RPMs are converted from hertz. The minimum and maximum RPMs varies by ton. This information can be found in the product data under “Sound Power Level (dBA)”. The suction temp, outdoor coil temp, and outdoor ambient temp inputs are all 10K ohm thermistors. The discharge temp is a 50K ohm thermistor. These ohm value charts for both types are readily available online. Pressure transducers take a 5 VDC output from the main PC board and provide a signal return between .5 to 4.5 VDC back to the board. This value is put through a formula to provide a pressure reading between 0 and 620.

Tip: By the math, the formula is trasnducer signal VDC (x) minus .5 times 155. Or 155(x-.5)= pressure. Examples: High 155(4.5-.5)= 620 PSI, low 155(.5-.5)= 0 PSI, mid-range 155(2.3-.5)= 279 PSI and 155(1.3-.5)= 124 PSI.

Validating the position of the EXV(s) is not possible. If it comes into question, you can verify the integrity of the stepper motor by ohming out each of its multiple coil circuits. You can also verify the 12VDC from the PC when commanding a position change. If both of these check out, then the internal valve is stuck or restricted.

The PFCM and IPM temperatures are built into the inverter which is not serviceable.

Once connected, the LED will turn green.

Tip: Only one device at a time can connect to a Bluetooth Module.

When the unit is found by the app, it will show the Serial and Model. If multiple units are near, it will show all available. Choose a unit and then touch “Pair”.

The app will take you to a connected screen with three choices:

“Faults”, “System”, or “Firmware”. Any active faults or required updates will display.

Tip: “Faults” will show you active and historical errors from the unit, not the system. If updates are required, turn your phone on do not disturb during the process. Any interruptions and you will have to start over.

Pesky P201 Code

Thu, 10 Aug 2023 16:55:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Pesky P201 Code

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

On 30RA to 30RB, this code can be a massive headache. With all the different options for these chillers can come with this alarm can send you down many different paths. We will break down a couple of basics to look at first to get the chiller back online. If this code still presents the chiller will not run.

The P201 Code read out is “Cooler Flow/Interlock Contacts Opened During Normal Operation”. This alarm is from the flow switch losing flow while the chiller has a run command active. This is the main safety for the water side of the chiller. This stops the chiller from freezing the evaporator barrel. This is why you never jump the flow switch on any style chiller.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

The first thing to look at when you have this alarm is to check if the chilled water pump is working. Once that is verified, check and make sure to use either a peach plug or the gauges on the piping. If you use the gauges on the piping, use only one gauge to pull the gauge from one side so you can have a standard. Once verified, pressure drop check the flow switch. Clean the flow switch if it’s dirty.

If the alarm is still present, replace the sensor – especially if it has been in the machine for a few years at least. Once all this has been checked, make sure you don’t have an external flow from the BAC. If that is all good hit the switch and fire the chiller up. These are some good steps to keep when checking water flow issues.

CODE 69: System Malfunction

Thu, 10 Aug 2023 12:13:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

CODE 69: System Malfunction

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

You may have seen Code 69 while receiving a service call to a 25VNA8-24VNA9 2 thru 5 ton. Many times we get a call from a tech stating “I think I have a bad board, I just want to verify with you guys!” Many times it is a bad board; or is it?

Do a literature search In HVAC partners or your Carrier Service Tech App, for this system and find code 69.

Sure enough the literature is almost always right. The literature does state Inverter/compressor internal fault. As stated above, also stated is overcharged system, phase imbalance/compressor or inverter miswire, flooded start, inverter damage, or compressor damage. But if the compressor isn’t starting, then you can’t check the charge. So lets focus on the inverter and compressor for this discussion. Maybe we’ll all learn something new.

You start thinking maybe the inverter is bad, or maybe the compressor is bad. First you can confirm that the MOC board is good. Ohm out the MOC board across A and B , you should get a good reading between 27K and 32 K ohms. Also the DC voltage on A & B should be around 3 vdc depending on incoming line voltage to the unit.

Then you ohm out the compressor wires from the inverter terminals U(YEL,), V (RES), and W (BLK). . You slide them off, ohm out and you begin getting some odd readings. You should get a stable, equal reading from the chart below, depending on which compressor tonnage you have. You should measure the resistance to ground from each lead. You shouldn’t get anything to ground.

You find the compressor resistance readings to be abnormal. Wow!! You begin to second guess your ohm/voltage meter. You change your batteries, or get a different meter. Having a very good workable meter is vital in this trade. So now you need to measure the resistance at the compressor fusite terminals. You will need to remove the sound barrier, a pain, but never the less, it must be done. During the removal of the compressor fusite cap, do not remove the RTV sealant. Remove the harness plug, measure the resistances, and compare to table 4. Once you remove the cap, you can measure the resistance at the compressor fusite terminals.. Recently, a tech removed the fusite cap, and found this:

If this tech had not removed the compressor sound blanket and removed the compressor fusite cap, he might not have found the melted power harness and melted compressor terminals. He probably would have believed the literature “inverter fault” and had to find this issue later. Then you have an upset customer because you didn’t go the extra mile and find the real issue. So next time you get a service call, make sure and make the proper checks before making the final diagnosis.

So what have we learned with this lesson:

Always follow the fault codes when you get a service call
The fault codes are listed in the literature
Take a look at all the fault codes under the listed code before making the final diagnosis
Make sure you have a good working meter; and a backup meter is not a bad idea
Safety first. Before checking any inverter, cut off your disconnect and give the inverter capacitors time to discharge
Most of the information you will need to troubleshoot Carrier/Bryant systems will be located in HVAC Partners
Code 69 means Inverter/compressor internal fault

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

The Magic Is In The Change

Thu, 10 Aug 2023 11:45:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

The Magic Is In The Change

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

What is superheat? What is sub–cooling? In this article we will review what refrigeration is, how it works, and some of the terminology. Hopefully, it will help you troubleshoot problems within the basic refrigerant circuit, and then apply these skills to more complex systems. For newcomers to the trade, this basic knowledge is critical. For seasoned veterans, a refresher never hurts.

The Basics

Refrigeration is the ability to move heat from a place it is not desired to one where it is unopposed. An air conditioner does not actually cool a space, rather it removes heat from it. This happens by utilizing the changes of state in refrigerant between liquid and vapor to reject and absorb heat. Refrigerants can be many things from water to CO2, or chemicals such as R410A, which is common in current residential and light commercial applications. Some refrigerants work better in specific temperature ranges and environments than others, but regardless of the type, the principles of refrigeration remain the same.

The Four Major Components of Refrigeration

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

How Does a Heavy Ambient Load Affect my Readings?

Suction and head pressures will be elevated. Superheat will vary depending on indoor and outdoor conditions. Sub-cooling will usually be lower than normal.

How Does a Light Ambient Load Affect my Readings?

Suction and head pressure will be diminished. Superheat will vary depending on indoor and outdoor conditions. Sub-cool will usually be higher than normal.

How Can I Tell if I have Non-Condensables in the Refrigerant?

Suction and head pressures and will be elevated. Superheat will usually be high and Sub-cool low.

***Tips and Tricks: The best way to verify if you are dealing with non-condensables is to pump the system down. Once the refrigerant is isolated in the outdoor unit, unwire the compressor and run just the condenser fan for about 10 minutes to acclimate the refrigerant. Then compare your refrigerant pressure against a PT chart. If it is higher than the chart, you have non-condensables.

What Happens when the Refrigerant Charge is Low?

Suction and head pressure will be low because there is not enough refrigerant in the system to complete the changes of state in the condenser and evaporator. Superheat will be high. There will be little to no sub-cooling.

***Tips and Tricks: You can use a thermal camera to see if a condenser is sub-cooling the liquid. In the following photos, the two units on the top have little to no sub-cooling while the two on the bottom have proper sub-cooling, as shown by the banding of color.

In the graphic, the red refrigerant line represents high-pressure vapor from the compressor. As this discharge vapor flows through the condenser, it rejects heat into the air, gradually changing state to a high-pressure liquid. This change is represented by colors transitioning from red to orange. The refrigerant continues to reject heat, becoming a liquid that is sub–cooled beyond its saturation point, shown in yellow. Then it flows to the metering device (TXV), which provides the drop in temperature and pressure. On the outlet side of the TXV, the refrigerant has transformed to a low-pressure, mostly liquid (mixed phase) state, represented by dark blue. As air is pulled across the coil by the blower, heat is absorbed from the air into the refrigerant causing it to change state from liquid to vapor, represented by the colors transitioning from grey to blue. The pale blue line represents superheated vapor that has absorbed heat beyond its saturation point.

Tips and Tricks: Latent Heat as Humidity

It is important to note that a second process of heat removal occurs in the evaporator when its surface temperature is below dewpoint of the air passing across it. A space with high relative humidity (latent heat) will affect the system’s ability to remove sensible heat from the air. This must be considered when diagnosing an issue or trying to get a refrigerant charge exactly right. As the humidity of a space falls in line, the performance of sensible heat removal will improve.

Why the Magic is in the Change

The HVACR industry almost exclusively uses the BTU (British thermal unit) as its measurement of heat. One BTU is the amount of heat or energy required to raise one pound of water by one degree Fahrenheit. This is a constant while the water remains a liquid between 32F and 212F. To transform this water into one pound of 212F vapor, it requires significantly more energy at 970 BTUs. Most of the work happens during the change of state. This principle is utilized in refrigeration by designing a system that can force the changes of state of a refrigerant from vapor to liquid, and then back to vapor again to move heat where we want it to go.

A Review of Terminology

Discharge is the high-pressure hot gas (vapor) refrigerant as it leaves the compressor. It maintains the superheat carried over from the suction. If it exceeds 225F, then the compressor oil may breakdown causing an eminent lubrication failure. Most compressors have an internal thermal switch that will open before it reaches critical temperatures.
Liquid is the sub-cooled refrigerant as it leaves the condenser after it has rejected enough heat to change state from a high-pressure vapor. Also, it is the state of low-pressure refrigerant leaving the metering device before it absorbs enough heat to change to a low-pressure vapor in the evaporator.
Suction is the low-pressure superheated vapor as it leaves the evaporator and travels to the compressor. A TXV type metering device uses a sensing bulb charged with the same refrigerant as the system to open or close, as needed, to keep an optimal amount of refrigerant moving through the evaporator coil.
Saturation is the specific temperature of a refrigerant at a specific pressure when in a resting condition. ***Tips and tricks: Knowing the exact temperature of a refrigerant drum (vs a PT chart) is a great way to calibrate the pressure on your gauges.
Superheat is the heat absorbed into a refrigerant above its saturated vapor point. This measurement tells how the evaporator is performing. High superheat means the liquid has boiled off too soon and the evaporator is starved for refrigerant. Little or no superheat means that the liquid is making it through the coil.
Sub-cooling is the heat rejected from a liquid refrigerant below its saturation point. This measurement tells how the condenser is performing. High sub-cooling means the refrigerant is backing up in the line from the metering device. Little or none means the high-pressure vapor from the compressor is not changing state properly.

Basic Refrigeration Diagnosis

1. Compressor: This is the heart of the system. Named for the job it performs, it compresses the low-pressure vapor into high-pressure vapor (discharge) and pumps the refrigerant through the system.

Compressor

2. Condenser: Half the magic happens here as high-pressure vapor pumped from the compressor rejects heat until it has changed state and condensed into a high-pressure sub–cooled liquid.

Condenser Coil

3. Metering device: This is where the refrigerant drops from high to low pressure and transforms to a mostly liquid with some vapor (mixed phase) state. Also, it regulates the flow of refrigerant through the evaporator.

TXV

4. Evaporator: The other half of the magic happens here as low-pressure liquid absorbs heat and changes state to a low-pressure superheated vapor. This vapor then returns to the compressor through the suction line.

Evaporator Coil

The Refrigeration Cycle in Action

What Happens if Air is Restricted through the Outdoor Coil?

The high-pressure refrigerant is hindered from rejecting heat and changing state to a liquid. Suction, head (liquid) pressure will be elevated. Superheat will be high and there will be little to no sub-cooling.

What Happens if Air is Restricted through the Indoor Coil?

The low-pressure liquid refrigerant is hindered from absorbing heat and changing state to a vapor. Suction and head pressures will be low with little to no superheat and elevated sub-cooling.

Dirty Evap Coil

What Happens when the System is Over-Charged?

Suction and head pressure will be elevated. There will be little to no superheat. Sub-cooling will be high as the refrigerant molecules stack up on the inlet side of the metering device.

How Can I Tell I have Bad Valves in the Compressor?

Suction pressure will be elevated, and head pressure will be diminished. Superheat will be high. There will be little to no sub-cooling. ***Tips and tricks: Try to pump the system down. If the system will not pump down or stabilizes at a positive pressure, without trying to bypass refrigerant, it is likely the valves will have failed.

What Happens when the Metering Device gets Restricted?

Suction pressure will usually be lower than normal. Head pressure may be elevated. Superheat will be high. Sub-cooling will be high as refrigerant molecules stack up on the inlet side of the metering device.

What Happens when the System is Over-Metering?

Suction pressure will be high and head pressure will be low. There will be little to no superheat and sub-cooling. The causes for this depend on the type of metering device.

How Can I Tell if I Have Mixed Refrigerant?

Suction and head pressures are usually elevated. Depending on the mix of refrigerant, superheat and sub-cool are completely variable. ***Tips and Tricks: This diagnosis can apply to some blended refrigerants that become fractured.

An old, printed copy of the chart below helped me immensely at the beginning of my service career. I hope it can help you the way that it helped me….

My Comfort Link Board is Not Working

Mon, 10 Jul 2023 15:30:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

My Comfort Link Board is Not Working

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Comfort Link controls on Carrier equipment have been around large package units to Chillers for about 15 years. It is a great control system for the ability to read codes and make changes on the machine without the need for computers or extra tools. The problem happens when it fails – you start having issues from burn inputs or outputs or internal shorts. Here are some tips on replacing and working with this board.

The Main Base Board or MBB is the brain of the control system. The MBB is the combination between a computer and an electromechanical board. This board holds all inputs from every thermistor to all transducers, it also is the ccommunication circuit between every auxiliary board on the unit. This board will allow you to run the entire machine per spec with just a start signal.

The problem happens with this board from burnt wires shorting the input side, to a simple hardware glitch that can kill the board. A common misconception when you order the board from the counter is it’s programmed to your exact machine. That is not the case. RCD puts out a base file for the serial provided. A very good practice before changing the bad board is going through the old board configurations. It will take about 30 to 45 minutes on the scrolling marquee. When you hit a setting and you don’t know what it is hold Enter and Escape for about 5 seconds and the display will read it out to you. This also works for the navigator which is highly recommended if you work on a lot of these (Navigator Part Number 30GT-911—062). Once you have the settings, swap the Enable/OFF/Remote switch to off and let the machine shut down. Lockout the power and swap the MBB. Once the MBB is swapped return power to the unit. With the enable switch off, go through your configurations and verify there are the same as what you wrote down. Once that is complete set the enable switch to where it was before, and you are ready to go.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

A2L Puron Advance (R 454b)

Mon, 10 Jul 2023 15:12:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

A2L Puron Advance (R 454b)

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

It’s coming soon. Below are the speculated dates of the release of Puron Advance, or R 454b in Carrier/Bryant equipment. These dates indicate readiness to ship the Puron Advance product. These are not hard cutover timelines. The speed of R 410a phase out will depend on factors such as demand, availability, and price of R 410a, state codes, etc. Actual first use of R 454b will be determined by the above factors.

In this article, we will cover a few key topics that will explain a few details pertaining to the use of R 454b. This information in this article only covers residential split ducted equipment. It does not apply to ductless, VRF, or commercial. We will cover ductless, VRF, and commercial, and more details on residential equipment in future newsletters. This briefing will give a few important details to prepare you for the change in refrigerants in Carrier/Bryant equipment. As always, safety is of main concern with the A2L refrigerants. A few things are still up in the air, under research and could change as new information becomes available. We will add new research changes in future articles and at our Fall and Spring Updates. But remember, as with anything new, keep yourself educated by reading and asking questions to learn as much as you can about new products. Much of the information in this newsletter is in Partners and My Learning Center.

Now we’ll talk about some primary concerns with equipment containing slightly flammable refrigerants. One of the primary concerns is the ignition of refrigerant leaking during equipment operation. Follow best practices when servicing the equipment to keep yourself safe and lower the possibilities of igniting any leaking refrigerant. One thing is for sure, be prepared and have a fire extinguisher available at all times when installing or repairing equipment with slightly flammable refrigerants. As mentioned earlier, a few things are still up in the air and could change as information becomes available.

Ignition

Most A2L refrigerants are difficult to ignite because they have a high MIE or minimum ignition energy. Many common household items like a cordless drill, toaster, hair dryer, or electric heater will not ignite A2Ls. They require higher concentration levels to achieve a flammable mixture.

Tools and Equipment

So what type of tools will be needed to work with Puron Advance? Well it requires the use of hand tools and equipment with no spark and no ark. Make sure all the tools that you are purchasing and using are UL certified. Your current gauges, digital or analog and hoses used with R 454b can be the same as used today, however, a dedicated set should be used the same as when working on R33 and 410a to avoid cross contamination. Check with the manufacturer to make sure equipment is rated for use with R 454b. 454b cylinders will have a red top and the hose connection will be reverse threaded. As always, before beginning work, make sure equipment is properly grounded.

Now we’ll talk about some primary concerns with equipment containing slightly flammable refrigerants, or A2L refrigerants. One of the primary concerns is refrigerants ignition of a refrigerant leak during equipment operation. We will cover this concern next in the indoor unit operation.

Indoor unit

There will be several component changes from the standard 410a systems. Indoor Equipment Indoor equipment will require an active mitigation board and refrigerant sensor. In other words, if refrigerant is present then equipment operation will be interrupted and the indoor fan will be energized to dissipate the refrigerant and lower its flammability level. The sensor will continually be scanning for R 454 b leaks. It will also have an updated wiring diagram. The indoor unit will have a sensor factory installed for vertical orientation, other location will be clearly identified for different applications. For furnaces only, you will mount the mitigation board to the side wall of the furnace in the blower compartment. 24 volts ac will power the mitigation board and Y/Y1 from the thermostat will connect to the mitigation board. The fan wire ( G ) from the mitigation board to furnace control board will control the fan if leaking refrigerant is detected. When powered up there will be a 10 second sensor warm up delay. After the warm up you can use the mitigation board self-test button to test the connection, this will have a 60 second mode. The mitigation board will have a green LED for normal operation, and a red LED for mitigation mode. When the mitigation board is triggered the safety chain interrupts Y/Y1 to the outdoor unit shutting it off. The blower will stay on for 5 minutes after the sensor readings are below mitigation level. After 15 minutes of mitigation the unit is allowed to heat or cool again. If the sensor over heats it will send the unit into mitigation mode. During this time the blower is always on in this mode.

The TXV will be designed for R 454b. New safety labels will be apparent throughout the indoor equipment.

Outdoor unit

We need to make sure the disconnect box is not mounted on the unit.

Pressures

Let’s compare operating pressure vs. saturated temperatures of R 410a vs R 454b. If we have a saturated suction temperature of 40 degrees Fahrenheit. The suction pressure of R 410a equals 118.8 psig. With R 454b, the suction pressure will be 113.3 psig . If we have a saturated condensing temperature of 110 degree Fahrenheit, the pressure of R 410a will be 366.4 psig. The R 454b pressure will be 349 psig. So these pressures are definitely not the same, but a small difference is apparent.

Future Research and Development

There is much more information forthcoming relating to R-454b. We are only scratching the surface. This newsletter may bring more questions than answers. That is OK. The more questions we get, the more we can all learn as we get the answers thru solid research and development. Remember as with anything new, research is constantly being conducted to improve the product. Change is inevitable as we find out new information. Stay tuned for much more in future newsletters.

Recap

R 454b will be the refrigerant of the future for residential equipment for Carrier and Bryant
You must have a fire extinguisher within your reach at all times
The equipment will have a mitigation board for safety
There will be a self-test button to check your safeties on the equipment
A set of separate gauges will be needed for A2L refrigerants (but should be common practice anyway for all refrigerants)
The pressures of R 454b are similar to R 410a
Technicians must read the literature before using A2L refrigerants to ensure safety. Go to My Learning Center to view much more information.
Read and learn as much as possible about any new products for safety for all involved
Much more information forthcoming as we learn more thru research and development
And always remember as with any new product, a few things are still up in the air and information could change as more becomes available.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

The Dreaded P4 Code

Mon, 10 Jul 2023 14:41:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

The Dreaded P4 Code

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

Have you ever shown up to a service call on a Carrier/Bryant/WeatherMaker (Midea) ductless system and found it locked out on a P4 or PC04 error code showing on the indoor display? Did the code return after a power cycle? Did the unit attempt to run? This article will help you understand what these codes mean and how to troubleshoot them effectively.

When working on any system, it is important to know the model number. These codes can mean different problems depending on the equipment, and where the error is displayed. In this article, I am referring to the following outdoor models:

(P4) 38MAQ, 38MBR, 38MHR, 38MPRA
(PC04) 38MAR, 38MPRB

Tips and Tricks: The following diagnostics can also apply to P6 and PC00 codes for IPM Protection

What do these codes mean? P4 and PC04 are Inverter Compressor Drive errors. Even though they sound specific, these codes can be generated from a broad spectrum of component failures and operating issues within the system.

Know your Voltage

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

Check the DC Fan Motor(s)

Does it spin freely? If not, then the bearings have failed. If yes, then ohm the windings from the UVW connector. It will be a much higher resistance than the compressor but should still be balanced between any two pins. It should not be open or grounded. On units with two motors, perform the process with each.

Read L1 to L2. What is the actual line voltage vs the minimum and maximum listed on the data plate? Read each leg to ground. Are they balanced? Check the main breaker, next the disconnect, and then the equipment. Was there any drop or difference in the voltage?

2. Condenser: Half the magic happens here as high-pressure vapor pumped from the compressor rejects heat until it has changed state and condensed into a high-pressure sub–cooled liquid.

Lightning prevails over circuitry

These components are integral to the inverter circuit. Capacitors can usually be found bad on a visual inspection. Failures in reactors are uncommon, and they can be easily overlooked. Reactors should ohm very close to zero resistance. They should never be open or have any continuity to ground.

Check the Compressor

If the fan motor windings read correctly, further investigation may be necessary. Turn on power to the unit. Some motors use feedback for speed recognition. During standby, 5 VDC should always be present on the 4 & 5 pins of the feedback connector.

Bad communication between the main PC and the Inverter can cause a P4 code. Check the wired connectors for poor alignment. This can happen when components are replaced, and someone pulled on the wires instead of the connector. Loose connections can wreak havoc on a communication circuit.

Example of a misaligned connector

Review of Possible Causes for P4 and PC04 Codes

High, Low, or Imbalance Voltage
Shorted PC and/or IPM Boards
Problems with the Compressor
Problems with the DC Condenser Fan Motor(s)
Faulty Communication between Main PC and IPM
Miswiring and Loose Connectors
Liquid in the Refrigerant (remote possibility)

Hopefully, the knowledge from this article will take some of the dread out of diagnosing a unit with these error codes and help you be more efficient when working with ductless products.

Replacing a part may remedy a symptom, but not necessarily the cause. Dirty power issues can be overlooked when components have failed. If left unchecked, voltage that is too high, too low, or imbalanced can make for recurring issues.

Understand the Inverter Components and Their Purpose

The first stop in the inverter power circuit is the bridge rectifier. Its purpose is to convert the AC line voltage to DC. In essence, it flips the bottom half of the sine wave to the top. The formula for DC output is 1.414 x AC line voltage. Next in the circuit are the reactor and capacitors. These components pull tension on and flatten out the sine wave. Then the IPM (Intelligent Power Module) or IGBT (Insulated Gate Bipolar Transistor) uses this voltage to send precisely controlled frequency to the compressor and DC fan motor(s).

After you have verified a good power supply to the equipment, perform a visual inspection of the wiring and circuitry. Some issues are more obvious than others.

Tree frog had a bad day

Check the Reactors and Capacitors

Ohm the Windings from the Wire Harness Connector

Has the sound blanket turned from green to brown? This is a sure sign it has overheated or possibly become demagnetized. Ohm the compressor windings. Remember, this is a three-phase motor. Your measurements should be balanced and less than 2.25 ohms. Nothing should read open or continuity to ground.

Ohm Values for the Windings of Select Model Compressors

Ohm the Windings from the Wire Harness Connector

If it is not present, you have a shorted PC board. If it is present, then progress to the next step. Rotate the fan by hand and measure pins 1 & 5, 2 & 5, and 3 & 5. If any negative voltage is displayed, then replace the motor.

Check The Inverter (IPM)

Learning to find all these check points on the back of a control board takes time and experience. Every board is different. If they do not have to be returned for warranty purposes, save your failed parts for practice and study tools.

Communication Is Key

I Need My Building Back Running Right NOW!

Mon, 12 Jun 2023 16:08:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

I Need My Building Back Running Right NOW!

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

With the current world of getting parts and lead times being what they are, sometimes you must improvise to get a machine up and going. This tip will help with bad thermistor probes on 30RB machines with Comfort Link Controls.

We have all been there on a roof from 7 o’clock at night to 3 o’clock in the morning on an after-hours call. The best part of the job, right? Especially this time of the year when Georgia is at its hottest. The machine is pulling Alarm P.97. You go into the current alarm menu, and you hold the enter and escape keys for 5 seconds. The panel reads out “Water Exchanger Temperature Sensors Swapped”. This code has a few different causes but the most common one is a faulty transducer. The others are listed as wiring errors or swapped sensors.

This code can hold this chiller from running. A good way to check the temperatures on the waterside is by laser probe or temperature clamp. You can verify the temperature reading with the temperature within the Comfort Link.

Use the following steps to verify the temperature reading:

Go into the comfort link panel under “Temperature”.
It will show “Unit” > Hit enter > EWT (Entering Water Temperature) is displayed > Scroll down once to show the LWT (Leaving Water Temperature). This will show what both sensors are reading.
If they are off, then you have a bad thermistor.

If it happens on the leaving water of the chiller, the chiller will not run for more than 5 minutes. This is because with a bad LWT the system will not process that it’s cooling.

When this happens, you can use the outside air thermistor. They are mounted on top of the control panel box. Verify that the temperature is reading correctly to outside conditions. You can swap this with your leaving water temperature thermistor to get the machine back online. The only catch is to make sure the bad thermistor is not reading cold. If it reads under 35 degrees, the chiller will not start.

This is not a permanent fix, but this will get the machine online. This can be used as well for bad suction transducers if the need comes up.

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

“FAIL TO PRESSURE” On A 48JC04-06 (Alert A321)

Fri, 09 Jun 2023 14:26:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

“FAIL TO PRESSURE” On A 48JC04-06 (Alert A321)

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

So, its Friday afternoon at 4:00 PM. You get a call of no cooling on a 48/50JC 04-06 Ultra High Efficiency Single Package Rooftop Unit with SystemVu™ 48JC04 – this system is one of Carrier’s high efficiency rooftop units. You open the system up and immediately go to the System Vu to check out the alarm. You see “Fail to Pressure”.

SystemVu Overview

Hold on, what is the SystemVu? Let’s check on this first. For the readers who aren’t familiar with System Vu, let’s do a brief review. This unit’s operation is controlled by the integrated SystemVu controller. It has been pre-configured with safeties, default settings and other logic to control all functions including the variable speed operation of the compressor, indoor fan motor and outdoor fan motor. It also controls the operation of factory options if they are provided. The unit can be hooked up to a conventional thermostat or Carrier sensor for operation with simply defining the sensor type mentioned in the manual. The factory default is Thermostat Control. In the manual are all the details to field change allowable settings to fit your application needs. For a quick start process if required, scan the QR Code below or enter the following URL. https://www.carrier.com/commercial/en/us/systemvu .

*IMPORTANT: This literature is in HVACPartners or Carrier Service Tech App, it covers the 48/50JC 04-06 models with SystemVu controls version 3.X. The SystemVu controls is standard on all 48/50JC models. Several SystemVu articles are written in previous newsletters that you may find helpful.

Fail to Pressure Error

So now that we know what the System Vu is (more to come in future newsletters) and where to find out more about the system Vu, let’s get back to our original subject – “FAIL TO PRESSURE”. We know from our experience as HVAC technicians, that “Fail to Pressure” means the compressor is not pumping. We go to HVAC Partners or the app, look up 48/50JC 04-06 and go to controls. Scroll down to alarms. We read “Alert A321 – C. A1 FAIL TO PRESSURE: This alert occurs when 20 seconds after the compressor turns on, the suction did not drop more than suction amount (CIR.A MIN SUC.P) and discharge pressure did not rise more than discharge amount CIR.A MIN DIS.P). This alert causes a strike for the compressor. The alert resets automatically. The cause of the alert is usually compressor wiring causing reverse rotation or a faulty compressor.”

We are thinking “Uh, Oh.” A bad compressor immediately comes to mind for many of us. Or, it could be a bad board. But more often, the board is not the issue. It couldn’t be a reverse rotation issue. Or could it? Let’s explore.

Troubleshooting the Error Code

First, cut the electrical to the system off, tag out and lock it out. Safety first! You can ohm out the compressor and check for good windings and ensure the compressor is not grounded, provided your volt/ohm meter is working properly and you have fresh new batteries in your meter. Follow the fault in the literature. Once you have confirmed a good compressor electrically (hopefully), look back at the literature again. Follow the offerings in the literature under this fault:

“Alert A321: The cause of the alert is usually compressor wiring causing reverse rotation or a faulty compressor.”

Begin asking questions to the owner such as:

Has anything happened recently to the building electrical wiring or system electrical wiring?
Has there been a recent thunder storm which knocked out electrical power in the area?
Have you called an electrician to do some work on your building electrical systems or panel box? Or was a main electrical transformer changed by the local power company in the area?”

Next, what does the literature state?

“The cause of the alert is usually compressor wiring causing reverse rotation or a faulty compressor.”

Now begin checking for reverse rotation of compressor which could happen with one of these episodes described above that could have caused a change of the 3-phase building wiring. So, reverse the line voltage by switching any two leads of the 3-phase wiring of the system at the system. Cycle the system back on, and your system begins operating. After a time delay, the compressor begins operating. Your suction pressure and head pressures are beginning to look normal. You have made the repair. You are the Friday afternoon hero! You repaired the system and it is now cooling down your customer’s building.

So, the next time you get a Friday Afternoon call on a 48JC system, don’t panic. Remember go to HVAC Partners. Look up the literature for this system, find your fault listed on the system Vu, and make the repair.

So, what we learned with this lesson:

The SystemVu is common to 48JC systems
You can work thru your control issues on the SystemVu Control
You can find out and read your system faults on SystemVu
Go to HVAC Partners to find the systems literature
Most of the information you need will be located in HVAC Partners
Safety first: Tag out, Lock out the disconnect to any system you are working on
Always make sure your voltage/ohm meter has fresh new batteries before you start the day
“Fail To Pressure”, means the compressor wiring causing reverse rotation or a faulty compressor
Reversing any two wires on a 3-phase system will reverse rotation, if needed

Source:

https://www.carrier.com/commercial/en/us/systemvu .
HVAC Partners: 48/50JC 04-06 Ultra High Efficiency Single Package Rooftop Units with SystemVu™ 48JC0; page 34
Carrier Service Tech App

Then press ENTER to choose the USB Product Folders:

Then select the Product Software: Once selected press ENTER.

Why Do Systems Freeze in Cooling Mode?

Fri, 09 Jun 2023 09:51:00 GMT

Anthony Coker

VRF Quality Assurance Manager Gulf Coast District

Why Do Systems Freeze in Cooling Mode?

June 10, 2026

L11- Detected indoor unit address, Flow selector unit not connected.

E17- Communication trouble between indoor unit and flow selector unit.

When troubleshooting any issue, it is always best to start with the most probable cause and work your way to the less likely possibilities. In this article, I will cover some of the basics of why systems freeze up during cooling mode. It might seem like HVAC 101 to some, but for the new talent coming into our trade, this knowledge can be invaluable.

Low air flow and/or low refrigerant through the indoor evaporator coil

It is important to understand that refrigerant pressure and temperature are relative. If the pressure drops, then the temperature falls accordingly. If the temperature falls below freezing, then available moisture in the air will turn to frost and eventually ice. This process usually begins just past the metering device. When left unchecked, it can work its way across the coil and back to the compressor.

How dirty is the filter? This should always be the first thing to check.

A blower motor must draw air in to move it properly. Low airflow because of a dirty filter can reduce capacity and cause a system to freeze. Closed supply vents on a system can also cause airflow to slow down through the indoor coil. However, these may not be the only issues. Make sure to inspect the entire system thoroughly for other potential problems.

Meter leads on the DFT position 1 and the C terminal.

Schematic: The circles represent where meter leads were making contact for testing.

The Pipe Sensor:

The pipe sensor monitors the temperature of the water going to a 2-pipe FCU, also known as changeover sensor, changeover switch, Aquastat, among others:

If the water is hot (> 83 F), it signals the thermostat that the system is in heat mode;
If the water is cold (< 65 F), it signals the thermostat that the system is in cooling mode;
User configurable for Open or Closed activation
Compatible with both on-Cool / on-Heat sensors (determined on 1st run setup)
Compatible with dry-contact pipe sensors (on/off), not analog. (ex. 10K ohm thermistor)

Dehumidify with Fan (Yes or No): when Dehum is active this setting specifies if you want the furnace/air-handler fan to run as well. This will activate (G) output on the t-stat at the same time. This can work independent of a cooling cycle.
Min Runtime Delta (2-10%): to reduce short cycling, the dehumidifier will run beyond the desired humidity by the selected amount (%). Default is 5%.
Dehumidify in Heat Mode (Yes or No): If humidity is a concern during the heating season and have a standalone Dehumidifier, this setting can be used to activate the Dehumidifier and will work independent of a heating cycle.
Dehumidifier Active (Open or Closed): this setting is dependent whether the HVAC system or standalone Dehumidifier requires it to be open or closed while active. This setting is part of the 1st run setup but can change afterwards in the Dehumidifier menu.

2. Condenser: Half the magic happens here as high-pressure vapor pumped from the compressor rejects heat until it has changed state and condensed into a high-pressure sub–cooled liquid.

Remind Your Customers to Change Their Filters Regularly. Photos Courtesy of Josh Petty

An undersized return can contribute to a system freezing.

While checking the filter, take measurements to know if the equipment has enough return air. A good rule is 2 cfm (cubic feet per minute) of air per square inch. Your local and state codes may vary. Most conventional systems are designed to deliver 350-400 cfm per ton.

For example: A 3-ton system moving 400 cfm per ton provides 1200 cfm and requires 600 square inches of return. For this system, a 20×30 return air opening is ideal. Ductulators, sizing charts, and apps are handy tools for verifying the proper size of ductwork.

What condition is the evaporator coil?

If it is within line of sight when checking the filter, take note of accumulation or damage. If it is not visible from the filter location, put forth the effort to visually inspect the coil. Knowing the condition will assist in your final diagnosis. If it is too frozen over, you may not be able to tell until thawed.

Does the blower motor run? No… Figure out why and remedy the issue.

Is the outdoor contactor stuck closed? Yes… Replace it.

The points below are common causes for an evaporator coil freezing.

Open blower relay
Failed motor and ECM (Electronically Commutated Motor) module
Loose or broken belt
Insulation sucked into the coil or the blower
Outdoor contactor stuck closed

Is the cased coil installed correctly?

Many applications will have a furnace that is narrower than the evaporator coil. Always follow the guidelines set in the installation manuals. Pay attention to how air flows through the coil. Make sure all areas are getting equal distribution.

Up Flow Cased "N" Coil Installation

Tech Tip: Never leak search a coil while ice is present. For many leak detectors, the change in atmosphere around thawing Ice can produce a false positive.

Is the metering device restricted?

Metering devices such as pistons and TXVs are a common place for a restriction. Filter driers can occasionally become clogged. Find this issue by measuring the temperature on both sides of the drier. A temperature drop indicates a restriction. The evaporator coil itself can become restricted. Diagnose by eliminating air flow and watching for irregular freezing patterns in the capillary tubes and individual sections of the coil.

Check The Inverter (IPM)

How does the refrigerant charge look? How is the flow?

Before you check pressures and temperatures, make sure the system is completely thawed. Any ice remaining will affect your readings.

Low suction pressure with little to no superheat, and (usually) slightly high subcooling indicates poor airflow through the indoor coil.
Low suction pressure with high superheat and little to no subcooling is a strong indication of low refrigerant charge.
Low suction pressure with high superheat and high subcooling are symptoms of a refrigerant restriction.

These results may vary based on many other factors in the system.

Frozen Coil from Low Refrigerant. Photos Courtesy of Joe Miller

TXV

Piston

Frozen Coil from a Restricted TXV. Photo Courtesy of Daniel Gaydos

Restricted Indoor Coil Found Using a Thermal Camer

Do you have a kink in the refrigerant line?

A severe kink in a line can cause refrigerant flash and a significant drop in pressure and temperature. Sometimes, it may be necessary to read temperatures at multiple points across the lines to find this issue.

TXV

Kinked Suction Line Found in a Wall Cavity. Photo Courtesy of Joe Miller

Is there a need for low ambient cooling?

In applications such as server rooms, systems will need to run in the cool mode year-round. If the refrigerant ever falls below freezing, it begins a steady process of forming ice across the evaporator coil. In situations where low ambient cooling is required, it may be necessary to add a freeze-stat to the indoor coil and/or head pressure control at the condenser.

This article has provided a basic understanding of why systems freeze up in cooling mode. Hopefully, it has helped to elaborate on how to understand and diagnose one of the main service calls faced in the HVAC industry.

They call me Dutch… Photo courtesy of Joe Miller

Wiring Tip for Zoning

Fri, 12 May 2023 13:37:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Wiring Tip for Zoning

When a house has zoning, it feels like there are wires going everywhere! And if you suspect that some of the wires may be crossed, you already know you could be in for a LONG DAY!!

It doesn’t matter whether its Infinity/Evolution, Honeywell, EWC, April Aire, or any other brand – we have a tip that can save guess work and give you confidence in the wiring.

When pulling new wires for zone installation or simply pulling a new wire for one zone, BEFORE you cut the wire off the spool, decide and announce a color or color combination. Use the SAME color(s) on both ends to be wrapped around the wire casing. THEN, no matter what the device is (thermostat, damper module, outdoor unit, etc.) when you get to the zoning board, where ALL of the wires meet up, you can KNOW what wire is going where.

Can’t remember where they go? Don’t remember what zone #2 wire is which? Pull zone #2 thermostat off and look at the wire color wrapped- now you know what wire is Zone#2 at the zoning panel.

Keep in mind you have to keep the same exact color(s) on BOTH ends of the wire.

The color chosen for my example were for an example, please choose the color combinations that best fit your job.

If you choose a color you later want to use, you could substitute it.

Here is an example of a 3-zone setup to show one possible way to help identify wiring at the zone panel:

The zone thermostats would be identified as #1-Red/ #2- Blue orange/ #3-Orange:

The zone damper wires would be identified as #1-yellow/ #2- Blue/ #3-green:

Zone equipment would be identified as indoor unit- blue black/ outdoor unit-blue green:

Now get out there and organize some zone wiring!

June 10, 2026

Bryant only:

Bryant Service Technician

38MU/40MU Crossover System

Fri, 12 May 2023 10:08:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

38MU/40MU Crossover System

In this article, I will explain how to wire the new crossover system for 24V communication or scenario 3 using a 3rd party thermostat.

There seems to be some confusion when wiring this system for scenario 3. Wire the system like any other multistage system. Wire the system for 3 heat 2 cool if you are using heat strips. The most important part of scenario 3 is setting the dip switches in the units.

First, set dip switch SW1 on the indoor unit. Also, SW1-1 and SW1-4 needs to be turned ON. This tells the indoor unit to look for 24V inputs like any other system.

June 10, 2026

The outdoor unit dip switch, SW1-2, needs to be set to ON. This also tells the outdoor unit to look for 24V inputs.

How I explain this to people when installing the systems is make it look like the picture in the install manuals.

Also, follow the wiring diagram in the install manuals and you will not have any problems.

Indoor & Outdoor Coil Cleaner

Fri, 12 May 2023 09:57:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Indoor & Outdoor Coil Cleaner

It’s that time again! Summertime is around the corner. Let’s get this ball rolling by checking out this coil cleaner by Totaline that can be used on both indoor and outdoor coils and is concentrated so that it can be adjusted as needed for the job at hand.

This coil cleaner (PMB23-054) is nontoxic when diluted and has vast capabilities when the mixture adjusted for the job at hand. For evaporator coils use the 1:8 ratio, 1 part cleaner and 8 parts water. Spray your coil and wait 10 to 15 minutes and rinse. You have a choice to use a hand sprayer to rinse the coil or let the coil rinse with the condensation. If you use it on the condenser coil you use it is a 1:4 ratio, 1 part cleaner and 4 parts water. Spray it and wait 10 to 15 minutes as well. Rinse. They say also that the coil cleaner is non-reactive to the aluminum, so it cleans the coil from dirt and debris and doesn’t hurt the coil. Here is the part number for it. P902-0301

They also have a special 32-oz bottle available only in HVAC TotalClean Kit Part Number P902-9901.

Remember safety first! View the SDS here .

Simplify your job and only carry one cleaner that can do both jobs and avoid confusion when grabbing the coil cleaner out of your van

June 10, 2026

Multiple Failed Parts

Fri, 21 Apr 2023 18:24:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Multiple Failed Parts

If you have multiple failed parts as part of a claim, you should enter each part on the same claim.

If the parts are listed on different Mingledorff’s invoices, you will just enter the corresponding invoice number next to the correct part.

See the example below which shows where you will enter this information on the Part Detail Information section in Service Bench.

June 10, 2026

Locating Invoice Numbers

Fri, 21 Apr 2023 13:48:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Locating Invoice Numbers

With our new system in place, there are three different numbers associated with your order:

Billing document / Invoice #
Sales order #
Delivery Document #

Any of these three numbers may be used in Service Bench in the replacement invoice number box, but please use just one.

June 10, 2026

Compressor

The invoice number can be located here on the invoice

You may also use the Sales Order number located on the Order Acknowledgement

From the packing list, please use either the number before the hyphen or the number after the hyphen.

For example: 0080053355 OR 0010027596

Do NOT use the entire number with the hyphen

If your replacement invoice generated from our previous software system includes a suffix, such as -00 or -01, do not include the suffix on your claim. Example: 910448

Overheated Thermostat

Thu, 13 Apr 2023 15:36:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Overheated Thermostat

Have you ever run across an overheating thermostat? Where the thermostat displayed 90 and the room temp was in the 70s or it was a runaway system? Did you know why? How did you fix the problem?

I run into this a few times a year. It is fairly easy to trouble shoot and fix. I see this sometimes with an Ecobee thermostat, but it can happen to any brand. The thermostat will be warm to the touch and will throw off the room temperature reading. This results in causing a runaway system in cooling or a possible no heat situation.

We see this problem with 2 stage Infinity/evolution systems wired non communicating. What causes this is the transformer in the outdoor unit is out of phase with the indoor transformer.

Troubleshooting this is easy:

1) Remove the Y1 wire from the outdoor circuit board.

2) Give a call for cooling, take one meter lead and place on Y1 wire and the other to SEC1 on the circuit board.

If the reading is 40VAC and above, the transformers are out of phase and one needs to be reversed. If the reading is 10VDC, the transformers are phased correctly. 40VDC and above will cause the thermostat to overheat.

June 10, 2026

Carrier/Bryant Service Tech App – Part 2

Thu, 13 Apr 2023 15:27:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Carrier/Bryant Service Tech App – Part 2

Last Month I demonstrated the Installation and basic usage of the app which included how to look up Literature scanning the bar. This month I am going to get into a more in-depth view of the Quick Links.

Literature Lookup

The first one is Literature Lookup. When you log in, scroll down to the bottom of your phone screen and you will see this menu.

When you type in the model number, the various literature available for that model will pop up and you can choose the one you’d like to view.

My Jobs

In My Jobs you can open create and close jobs.

Troubleshooting

If you click Troubleshooting and see the screen to the right, you will need HVAC partners credentials to enter this link. This is an awesome tool to troubleshoot certain systems the easy way with Interactive Troubleshooting which is in its Beta Version as seen below.

Parts Cross-Reference

June 10, 2026

Infinity/Evolution Inverter Units

Thu, 13 Apr 2023 15:12:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Infinity/Evolution Inverter Units

When it comes to working on the infinity/evolution systems, there are several inverter-driven outdoor units. They all have nicknames, different specification, and different diagnostic methods. For the average technician, it would be extremely difficult to memorize all of this data.

How can you tell them apart?

For starters, they all have a different SEER rating, this make them have different model numbers (3 different HP and 3 different AC). Second, the inverters have different manufactures, so they physically look different. I have collected a picture for the electrical section for each different set of models. I will group them with interesting facts about the models along with their nicknames. I like to tell people: we have three at this time, and as each Ac/Hp increases with seer, the number of components in the electrical section increases.

1. The first in SEER sequence is the HP 18 SEER/ AC 19 SEER. It is nicknamed the 5 STAGE. It is recognized by having an “all in one” inverter, all of the components are tucked very tightly into a single kit.

Inverter made by Toshiba
Typically, 25%-100% in “5 stages”
Rotary compressors
Outdoor fan motor is 3 phase
Model numbers: 25VNA8/ 24VNA9 & 288BNV/189BNV

2. The second in SEER sequence is the HP 20 SEER/ AC 20.5 SEER. It has two nicknames: Greenspeed/ Extreme & 1st Gen Greenspeed/ 1st Gen Extreme. It is recognized by have the inverter at the top in a black box, with 3 items below it: control board, transformer, and a contactor.

Inverter made by Emerson
Typically, 40%-100% all variable
Scroll compressors
Outdoor fan motor is ECM
Model numbers: 25VNA0/ 24VNA0 & 280ANV/180CNV

3) The Third in SEER sequence is the HP 24 SEER/ AC 26 SEER. It is nicknamed: Next Gen Greenspeed/ Next Gen Extreme & 2nd Gen Greenspeed/ 2nd Gen Extreme. It is recognized by have the inverter at the top in a white box. Then several more items mounted below: control board, transformer, filter board, reactor(s).

Inverter made by Samsung
Typically, 25%-100% all variable
Rotary compressors on 2/3/4 tons & Scroll compressor on 5 ton
Outdoor fan motor is ECM
Model numbers: 25VNA4/ 24VNA6 & 284ANV/186CNV

June 10, 2026

Bryant only:

Bryant Service Technician

38MU/40MU 18/8 Low Voltage Wiring

Fri, 17 Mar 2023 10:26:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

38MU/40MU 18/8 Low Voltage Wiring

This month, I will be covering how to properly wire a 38MU/40MU for 24V operations and setting up the DIP switches.

I hate to say this, but the install manual is poorly written and many people get confused on why the unit does not operate on start up. Most of the confusion is understanding the DIP switches.

Many contractors are using this equipment with an Ecobee or similar type thermostat. The system can be configured several ways. When you wire this system for 24V, wire it like any other multi stage system using 18/8 wire. The part that trips people up is properly setting the DIP switches.

The indoor unit has 2 DIP switches that will need to be set and the outdoor has one.

The indoor DIP switch SWl-1 and SWl-4 will need to be turned on. The wiring diagram shows the correct location.

The outdoor unit has 1 DIP switch which needs to be turned on, SWl-2. Turning on the DIP switches tells the unit to look for 24V inputs instead of the communications RS-485.

Set the switches correctly and you should not have any problems making the system run on 24v.

June 10, 2026

Voltage Drop on Contact Points

Fri, 17 Mar 2023 10:11:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Voltage Drop on Contact Points

Most technicians know about checking capacitors under a load while a motor is running, but did you know that you can do the same thing with contact points!?

That’s right, on contactors you can actually inspect the points for quality BUT you cannot verify that the points are making good contact. Furthermore, you cannot see anything about relay contacts at all.

*** Before checking anything, please touch your leads together using ohms to verify the meter reads 0.0 (zero). Anything that the meter reads above Zero is how off the meter is. ***

One method that is time consuming for checking contact points: Unwire everything on the line voltage and to energize the coil. Use an Ohm meter to verify the resistance of the points. Anything reading greater than (1) one ohm is considered a bad connection.

One quick method for checking contact points is using voltage drop. This will be tested while everything is properly wired, and the relay or contactor is energized (for normally open contacts). With a voltmeter, you place the leads in parallel with the contacts. This means that the leads will be in contact with both terminals/wires that feed the contacts. This test will be performed on the same side of power. If you know that the proper voltage is being applied, then the voltage drop should be (0.0) zero. Anything that exceeds 5% (five percent) of the voltage being applied to the contacts is considered excessive and would require replacing.

I have taken pictures of a 2-pole contactor, 2 different relays, and a sequencer; these are commonly seen devices in the HVAC industry. The meter leads in these photos represent examples of checking in parallel with the contacts. Again, the method described in this article is for checking Normally-Open (NO) contacts while the devices are energized. This test is not limited to the devices listed but rather a test that can be utilized across the industry. Anything that is a “switch” likely has contacts in it, if so, then this can be utilized to verify that contact points are making good contact.

MATH EXAMPLES for Voltage drop:

If the voltage to your contacts is 236 Vac:
236 Vac Multiplied by (0.05) = 11.8 Vac
8 Vac or higher is considered excessive.

If the voltage to your contacts is 118 Vac
118 Vac Multiplied by (0.05) = 5.9 Vac
9 Vac or higher is considered excessive.

If the voltage to your contacts is 26 Vac
26 Vac Multiplied by (0.05) = 1.3 Vac
3 Vac or higher is considered excessive.

June 10, 2026

Bryant only:

Bryant Service Technician

Carrier/Bryant Service Tech App

Fri, 17 Mar 2023 09:54:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Carrier/Bryant Service Tech App

When I instruct Nate Classes, I typically suggest the Carrier Service Tech App to techs that have not used it. I have them download it and install it. Then, I have them open it and they have a couple of things to input. Once they begin to use it they love it, just as I did!

I will go through logging in and the My Jobs Quick Link in this article. In subsequent articles, I will demonstrate the use of other quick links. This app is a powerful tool for technicians in the field.

Download and Install the App

Search for the Carrier Service Tech app in the App Store or Play store. Click to download & install the app. Once installed, open the app.

Signing in to the App

Once you open the app, you will have to agree to terms & conditions and set your location preferences. Then, you will reach the Sign In screen. Enter your HVACpartners account information.

The app will prompt you to set your favorite store. Once completed, you will access the home screen.

Barcode Scanner

The barcode scanner button allows you to scan the model number barcode for easy access to information on that particluar model.

Feel free to explore the app and all the different information it provides.

June 10, 2026

How to Set Up and Access the Dealer Portal

Thu, 16 Feb 2023 13:58:00 GMT

Anthony Coker

Technical Services Manager Southwest District

How to Set Up and Access the Dealer Portal

We all know how complicated Infinity and Evolution systems can be; wouldn’t it be nice if you could see operation data and fault codes without you actually being at the house? This is a real achievement that could be done as long as the homeowner has Wi-Fi and you (technician) are registered in HVACpartners under a Carrier or Bryant account. This remote monitoring center is called the “Dealer Portal” and/or “Connected Portal”.

Why would you need to see operation data and error codes remotely, and how could this be useful?

The data that will be shown on the Dealer Portal is dependent upon what type of equipment that customer has. For example, if it is a non communicating outdoor, you would simply see if it is being commanded on/off and you would see faults pertaining to an indoor unit only; whereas if the outdoor was a communicating unit with an inverter, then you would actually see refrigerant pressures, compressor RMPs, line temperatures, superheat, and basically everything the wall controller would tell you if you were on the job standing in front of it.

You would have access to see the last 10 fault events, the units running CFMs and possibly even the running pressures. The model and serial numbers are viewable for all communicating equipment that is installed at the customer’s residence. This information could help you diagnose what may be the problem and give you enough information about the units to take the needed part with you to the job.

Lastly, in the event that the unit acts up or faults out while you are not on the job, or has a pattern for faulting at night: you could use the Dealer Portal to monitor the system and see what it is doing at the time the unit malfunctions. If the unit is registered in the Dealer Portal, then you could call on a Mingledorff’s Technical Service Manager to access it and review how it is running. Configurations can be changed in the unit (if needed) through the portal, but only by the dealer.

Let’s get the customer on the portal:

Have the customer sign in with their credentials here:

www.myinfinitytouch.carrier.com

www.myevolutionconnex.bryant.com

Once logged in, click on “My Locations” shown below. This will populate any locations/ homes registered to the account.

Within the locations, Click the location you want to add to the portal on the drop arrow circled in purple . This will open up the units registered to their account for this particular location. From here, click on the unit drop down arrow circled in blue . This will reveal loads of information about the system. Go ahead and scroll down to the bottom of the system information and look for Dealer information for the next step.

If the customer has never had a dealer connected it should say “confirm your dealer” or either “select a different dealer”. I have circled this in yellow. Click on it. A popup screen will appear for an “edit system” screen.

On the “edit system” popup screen you will need to click the text again that will read either: “confirm your dealer” or either “select a different dealer”. I have this located with a red circle. When clicked another popup will appear for a screen labeled “select an expert”.

On this “select an expert” popup, enter the zip code, and search. Local Carrier/ Bryant dealers should populate. Find your dealership and click select, I have shown this with an orange circle. When pressed, the “select an expert” popup will go away and you will be back on the “edit system” popup.

When you return to the “edit system” popup screen, scroll all the way to the bottom. I have put green squares around 3 checkboxes that need to be checked. After checking the boxes, you must click the “saved” button shown in the red square.

At this point the unit has been registered to the Dealer Portal. Please allow 24-72 hours for the servers to sync with new changes. The servers will then show the added unit under the dealer’s name within the portal.

How to get into the portal

After the allotted time has elapsed. Go to:

www.hvacpartners.com and sign in.

I show the pathway through the drop-down menus in the following picture:

Marketing/ Dashboards & Portals/ Connected Portal. Click the connected portal.

If you are a dual branded dealer, then both Carrier and Bryant will appear. If not, you will only have your brand. Click on the needed portal to continue.

When you click on your portal, the following screen should appear. If you click on “customer” (in the orange square) a list of customers who have chosen you as their dealer will appear. To view the information about their system, click the “details” tab in the red square.

From here you can see the entire communicating system and all associated software versions along with model and serial numbers. In this example you can see by the two green boxes for the wall controller, that this customer only checked 2 or the 3 check boxes. To view more in-depth information about the equipment you have to click one of the blue “details” tabs

Below is the view after clicking details:

You can see the list that can be expanded which I have circled in purple.

I have cropped some screens, and modified the serial numbers to keep certain dealer and customer’s information private. Setting the customers up on the portal is an easy process and could reap many benefits. Carrier and Bryant are going to begin utilizing this portal more with new upcoming equipment.

Get out there and get connected to the portal!

June 10, 2026

Bryant only:

Bryant Service Technician

Late Friday Night

Thu, 16 Feb 2023 10:52:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Late Friday Night

It’s late one Friday night and you are on a call with a bad OFM (outdoor fan motor). The OFM has seized bearings and you don’t have a replacement on your truck. What do you do? How can you get the customer going?

As field technicians, there isn’t always a by-the-book solution to solve a problem. I want to encourage all techs to think outside the box when solving problems in the field. There is an emergency temporary solution to this; HOWEVER, I caution to only use this as an emergency solution. If you receive a call regarding a bad OFM which is seized and need to buy a day or two to get the correct OFM, here is a trick that may help the customer and you.

Most likely the bearing has dried out and seized. You may be able to do this without completely removing the OFM. Start by removing power from the unit. Next, remove the OFM from the unit. Drill an 1/8” hole in each bearing cap on each end of the motor.

Take your favorite oil/lubricant and spray in the hole you just drilled. This part may take a few extra minutes. Slowly start rotating the fan shaft back and forth until the shaft spins free. You may need to use a small adjustable wrench to help rotate the shaft making sure not to damage the shaft in this process.

Lastly, reinstall the OFM in the unit and turn the power on. I highly recommend taking amp readings from the motor to ensure the motor is not over amping. After all this is done, please visit your local Mingledorff’s to get the correct OFM.

June 10, 2026

Dual Inlet Backward Curve Fan Installation

Thu, 16 Feb 2023 09:58:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Dual Inlet Backward Curve Fan Installation

The models listed at the end of this newsletter are designed to meet federal Fan Energy Rating (FER) requirements and are scheduled to be released into production. These furnaces use a dual-inlet backward curve fan wheel. The installation of these wheels into the blower housing and onto the motor shaft during service or replacement varies slightly from current standard field installation practices.

Technical Information:

Typical installation of traditional blower wheels requires you to slide the wheel on and center it into the housing. For the new wheel and motor design, the installer, after completing installation of the motor to the housing, will slide the blower wheel to the stop mechanism designed into the flat of the motor shaft per Carrier’s Specifications.

Carrier’s Installation instructions for the blower wheel are as follows as per TIC 2019-0012.

Installation of the DIBC wheel:

Lay blower housing on non-motor side
Insert DIBC wheel into blower housing
Place blower housing orifice onto blower housing, aligning motor mounting holes
Install motor shaft into hub of DIBC blower wheel
Align motor mounting arms and install 4 motor mounting screws. Tighten motor mounting screws to 40 in-lb.
Upright blower housing assembly
Align set-screw with flat on motor shaft
Push blower wheel toward motor until wheel hub bottoms out on the motor shaft and tighten set-screw to 160 in-lb.
Spin blower wheel and check for interference. Adjust as needed.
Install blower cutoff in housing
Install green ground wire from motor harness to sheet metal of housing
Reinstall blower housing mounting brackets to blower housing and install into furnace

Models Affected

Carrier

59SC5B040E141110
59SC5B060E141112
59TP6B040V141110

59TP6B060V141112

Bryant

915SB30040E14A-A
915SB36060E14A-A
926TB30040E14A-A
926TB36060E14A-A

Payne

PG95ESAA30040AAA
PG95ESAA36060AAA
PG96VTAA30040AAA

PG96VTAA36060AAA

June 10, 2026

Flame Simulator

Thu, 12 Jan 2023 15:31:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Flame Simulator

You go on a no heat call on a gas pack/ furnace. All the burners ignite, but then go out followed by the furnace showing an ignition failure code. After cleaning or replacing the flame rod, the furnace gives the same trouble. So, what now? What is the faulty component? The sensor, sensor wire, ignition board, or grounding?

There is a tool that can be used to verify the circuitry for the flame sensor. This tool can help you troubleshoot the components involved, which can prevent replacing parts that are not bad. We call this tool a “Flame Simulator”.

Safety First:

THIS TOOL SHOULD NEVER BE LEFT IN A UNIT BEYOND THE PARAMETERS OF TESTING. DOING SO WILL DIRECTLY VOID THE UNIT’S UL SAFETY LISTING.

What does it look like?

This tool is homemade and is a fraction of the cost of a store-bought simulator. There are a couple brands out there that can be purchased, but they are hard to find. It is customizable in the sense that you can add a small amount of wire to it or even an alligator clip to the bare end.

How is it made?

It is best to solder the connections to ensure they do not come loose.

How to use it

Remove the female crimp connector from the flame rod within the unit.
Connect the female connector to the male spade of the simulator.
Call for heat on W1 with gas on or off.
When the gas valve receives 24vac, touch the other end of the simulator to ground in the unit. If you have spark ignition, it will be sparking at this time. If you have Hot Surface Ignition then there will be a short period after it glows before the board is supposed to send 24vac to the gas valve.
If you touch it to ground too early, the unit will give an “abnormal flame-proving signal” meaning: flame is proved while the gas valve is de-energized.

This will tell the board that the flame exists.

Results

If the unit repeats the ignition failure when using the Flame Simulator:
First: Verify that all of the ground wires are intact in the unit, primarily on the gas valve and the ignition board.
Second: Try the same test with a new wire from the board to the simulator.
Lastly: replace the control board.

If the unit does not give an ignition failure code while using the simulator but does when connected to the flame rod:
1st- clean the flame rod again
2nd- verify the DC Microamps while in series with the flame rod (Carrier is typically 4-6)
3rd-replace if out of range or in the bottom of the range (less than 5)

The items needed to make the Flame Simulator are best bought in multiples, so you should make your HVAC buddies one as well. Always remember, this is a tool and not a part.

June 10, 2026

Bryant only:

Bryant Service Technician

DUCKT-STRIP Wiring

Thu, 12 Jan 2023 14:25:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

DUCKT-STRIP Wiring

DUCKT-STRIP wire is a great product for ductless units when used properly. The wire is used to power and communicate between the indoor and outdoor units. It also can be used to solve E1 fault code problems, which I covered in previous article.

June 10, 2026

The wire is designed to not have interference on the “S” wire or the 3 wire depending on how the unit is labeled. They do this by spacing the S wire away from the L1 and L2 with the ground wire in between.

When the wire is stripped back, you will see a black wire, white wire, bare copper wire and the red wire.

L1-black, L2-white, bare copper wire is earth ground and the red is S or signal wire. Depending on how the unit is labeled it could be 1 2 3. 1-L1 2-L2 and 3 is S or signal.

If wired wrong, and some people do, you can get an E1 fault code. E1 is communication failure between the indoor and outdoor unit. Some people think the red needs to land on L2 or 2 terminal and white wire on S or 3 terminal. If this happens the S wire is right next to a high voltage wire and could possibly induce a volts over on the signal wire causing the communication to scramble and get the E1 fault.

Follow this wiring and you should not have any problems.

Terminals for the indoor unit:

L1-BLACK WIRE

L2-WHITE WIRE

GROUND-BARE COPPER WIRE

S-RED WIRE

Totaline Slime Prevention & Removal

Thu, 12 Jan 2023 14:08:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Totaline Slime Prevention & Removal

TIC2021-0006 states that a slime has been detected in condensate lines, traps, drains and pans. From TIC: “The slime is what is called a biofilm and it is a natural defense mechanism of many microorganisms or bacteria. The slime forms around bacteria and acts as a protective armor for the bacteria. Nutrients and moisture can pass through the biofilm but many chemicals that can harm the bacteria have more difficulty passing through the biofilm. Air Conditioning coils cool the air passing over it and dehumidify the air creating condensate. Airborne bacteria can collide with condensate droplets and become entrapped inside of the droplet. The droplet can then transport the bacteria through the entire condensate management system. Bacteria will accumulate in any area that does not dry out and has very slow-moving condensate.”

It also says “The ideal habitat needs to be absent of extreme temperature swings, UV light or harsh disinfectants. A consistent supply of moisture ensures that the bacteria will not dry out and die. These condensate management systems include all field installed piping are not unique to Carrier, and thus can be considered an industry wide issue.” There is not a solution at the moment to fix this but it is in the works.

Further testing shows that UV lights reduce growth in close proximity. However, when the light is out of sight, the heat from the UV light makes it grow faster. Also, using “antimicrobial impregnated materials have limited effect on the rate of microbe growth because either the antimicrobial material leaches out of the system and becomes ineffective, or a layer of dead bacteria forms on the surface protecting future bacteria growth.” They ask you not to use bleach because it breaks down some components and becomes neutralized as quick as it attacks the biofilm.

A combination of a cleaning method below along with regular monitoring for system blockages or backups will be needed. Each application will have a different amount of time required to block the drain lines, but the methods below will help minimize regrowth rates of the biofilm.

June 10, 2026

Carrier’s Recommended cleaning method:

Remove as much water and biofilm as possible from coil and pan with vacuum.
Flush with large quantities of fast-moving water.
Optional – Use one of the cleaning chemicals listed below in order to delay regrowth.

Directions for completely blocked drainage systems with accessible drain terminations:

Vacuum out any slime located in the drain pan or on the fin surface.
Optional – Pour 2 quarts of Totaline® Cooling Coil Treatment P902-1101 and let sit for 10 minutes.
Fill drain pan with clean water.
Attach vacuum hose to outlet of the drain termination and vacuum all liquids out of drain pan.
Flush system with either 5 gallons of water or with a hose. For maximum effectiveness when using a bucket, be sure to fill drain pan as much as possible without overflowing.

Directions for completely blocked drainage systems without accessible drain lines:

Vacuum out any slime located in the drain pan or on the fin surface.
Optional – Pour 2 quarts of Totaline® Cooling Coil Treatment P902-1101 and let sit for 10 minutes.
Insert a hose to the inlet of the drainage system in the drain pan and turn on faucet. Allow system to build pressure to dislodge blockage and then allow ample water to flow once blockage is removed.
If blockage does not come free before drain pan fills with water, remove hose, run a long, small wire brush through the drainage system to mechanically dislodge the blockage and then repeat previous step.

Directions for drainage systems that have been partially blocked:

Vacuum out any slime located in the drain pan or on the fin surface.
Flush system with either 5 gallons of water or with a hose. For maximum effectiveness when using a bucket, be sure to fill drain pan as much as possible without overflowing.
Optional – Use Totaline® Cooling Coil Treatment P902-1101, add slowly allowing chemical to interact with biofilm in drainage system and then flush with large quantities of water.

Directions for a continuous disinfectant method between preventative maintenance:

Use Totaline® Condensate Pan Strip P902-38003 through P902-38007 based on size of the cooling system.
Place close to the drain pan outlet. Testing has shown to delay the growth of biofilm downstream of the pan strip.
This product is currently available in the following states: AL, AR, CO, CT, FL, HI, LA, MA, MD, ME, MS, NC, NH, NJ, NY, OK, PA, RI, SC, TN, TX, VA, WV. Certifications for additional states are currently being pursued.
Strips will need to be replaced and a new strip inserted on a regular PM schedule.

Adaptive Heat

Wed, 21 Dec 2022 16:37:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Adaptive Heat

If you have a 2-stage performance furnace, you have a heat mode called adaptive heat. Adaptive heat can be controlled with a single stage thermostat on a 2 stage performance unit with a call for heat on W1. The furnace control CPU determines what stage (low or high stage heat) is required based on stored previous run time.

The furnace will start with either low or high heat. If the furnace starts in low heat, the CPU will determine the time before switching to high heat. The time is 0-16 minutes. After 16 minutes, high stage will come on and stay on for the remaining of the heat cycle.

This can be very useful if there are not enough thermostat wires for 2 stage heating or a simple single stage thermostat is needed. Having a 2-stage furnace controlled from a single stage thermostat is a handy feature to have.

June 10, 2026

Pressures Not Reading Right?

Tue, 20 Dec 2022 14:05:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Pressures Not Reading Right?

Have you ever put your gauges on a unit and notice that the pressure reading rises slowly, shows Zero but only on one side, OR while trying to add refrigerant, it just doesn’t seem to be going into the unit?

At this point you know that there is a flow or connection issue with the unit. Here are a few steps you can follow to get accurate pressures from the system to the gauge and get refrigerant to flow faster:

For starters let’s discuss the two MAIN types of valve connections:

1) The standard shrader which has an internal replaceable valve core:

This is a Carrier residential Liquid Line Service Valve and the core within it.

June 10, 2026

Bryant only:

Bryant Service Technician

2) The CoreMax which is mostly seen on Packaged Units:
This Valve is an all in one and shouldn’t be disassembled any further

Both of these valves work with the same process. “Something” pushes on the STEM circled in green which then pushes down on and separates and opens the gasket- pointed out in blue. If these stems are not depressed then the gaskets will not be released.

Now that we have covered what has to happen, let’s figure out why it isn’t happening.

If you look at your hose connector:

In the center of the gasket within your hose connector there is a device called a “Depressor.” You can use the slotted top of your Tstat screwdriver to raise, lower, or remove this depressor from the hose connector.

As you move throughout your day, moving from unit to unit, take notice that some valves allow the “valve core” or stem in the CoreMax to sit LOWER than normal (resulting in them not being depressed when you gage up to the unit) or HIGHER than normal (This can push the depressor further into your hose connector)

It is a good idea to regularly check on the depressor height in your gauge connector to ensure that the pressures brought to your gauges are right. Looking at them also ensures that you’re looking at the gaskets so you know when they need to be replaced.

Now get out there and keep your depressor height right!

Because I was Inverted

Thu, 17 Nov 2022 10:35:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Because I Was Inverted

For this article, I will explain how to replace the main control board on a 38MARB ductless outdoor unit. The boards are inverted or upside down in most ductless outdoor units.

The 38MARB board has a heat sink under the board that you cannot see with a refrigerant loop running through the heat sink. At first glance, it looks easy to replace, and it is; however, if you do not know about the hidden screws you could damage the refrigerant loop when trying to remove the board.

Start by removing power to the unit and confirming with a meter. Remove the top cover and the fan side cover exposing the board, fan, and compressor section.

Then remove the wires from the board (this will help when it is time to flip the board over). Next, find the pigtail for the compressor harness and disconnect.

Next, locate the wiring diagram on the board. Once located, take your finger and move it around the board feeling for round holes under the diagram. There are four screws holding the heat sink to the board and three are under the wiring diagram. It is best to insert a #2 Philips head screwdriver through the thin wiring diagram and remove the screws.

Once all four screws are removed, locate the small plastic clips on the front and back of the board and gently release with a flathead.

Simply lift straight up off the heat sink and lay it to the side where the copper and electrical are located. Finish removing the remaining wires and start the new board installation. Remember to add new heat sink paste to the heat sink. If this is not completed the new board may not last long.

Install the new board, assemble the unit, restore power, and check for normal operation.

June 10, 2026

Cleaning Coils

Thu, 17 Nov 2022 09:17:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Cleaning Coils

Fall is the time for the leaves to fall and with the mixture of rain and wind tends to stir up debris that can cause your outdoor coil to get dirty along with all the natural elements that cause deposits to attach to the coils. With that said, we want to make sure that we are cleaning the coils properly and to Carrier specifications to extend the coil lives longer.

The most important thing to remember is safety first. Always wear the proper PPE (Personal Protection Equipment) when working with chemicals and always be aware of the SDS (Safety Data Sheets) as to be aware of what steps to take if ingested, inhaled, or if it gets on your skin and the things to do for protection along with precautions that you might be or not be aware of!

Now that we are past all the boring stuff, let us get down to the good stuff!

Coil cleaners come in a variety of strengths and concentrations that need to be taken seriously. An example would be: if you washed your clothes with pure bleach what would happen? Nothing good I can guarantee that! You will want to read the labels on the containers to make sure you have the properly mixed solution. You will have a label on every container size that tells you the proper ratio for mixing the cleaners with water to dilute it to the specified ratio required to do the best and safest cleaning job possible. If you go over it, it can do more damage than good by eating or breaking down the elements that make up the coil. Too little and you don’t have a clean coil.

Just a few part numbers of the variety of coil cleaners available!

P902-0101, P902-0301, P902-1001, P902-1801

Below are photos of coil cleaners and their labels so that you can see the mixing ratios and instructions of use.

June 10, 2026

When you use any coil cleaner, you should clean out all debris from cabinet before using so that it can drain properly. Proper drainage can increase efficiency. Rinse thoroughly and always use safety!

Furnace Rapid Flash

Thu, 17 Nov 2022 08:55:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Furnace Rapid Flash

This article is in reference to non-twinned furnaces. Pictures are shown of a Carrier 58STA110-13122

The manual and sticker for Carrier/Bryant/Payne furnaces show the following:

June 10, 2026

Bryant only:

Bryant Service Technician

At first glance, this seems simple. Just swap the two incoming power wires, right? But the furnace has been running for years at the home with no issues and swapping the wires produces the same rapid flash situation…. What gives?

Let’s tackle how to attack this fault:

FIRST , trace the wires or read the schematic to determine where L1(black) and Neutral(white) land on the board- Pointed in green. Use a voltmeter to Verify the follow:
L1-N= 120vac
L1-Ground=120vac
N-Ground=0vac
This will verify that the ground to the equipment is good and that L1 is the HOT wire and not N. ***If L1 to Ground is 0vac and N to Ground is 120vac then simply reverse the two wires as they wire nut to the furnace power in the Junction Box highlighted in Purple.

Second , Use the Voltmeter to check AC voltage from R (on the screw terminal strip) to L1. This test SHOULD read mid-90’s, my test produced 93.4Vac shown here:
This picture is an actual reading with my meter as well as a layover of the schematic showing the terminals that I am checking.

This test will verify that low-voltage R is truly the hot wire. IF this test produces roughly 145 Vac then this means that the transformer low voltage is out of Phase. *** The easiest way to correct this is to swap SEC-1 & SEC-2 on the board. (this is commonly seen when people replace transformers on furnaces)

Third , if the high voltage and low voltages have been checked for proper phasing and they are correct, and the board is still showing a rapid flash, at this point it is recommended to replace the furnace control board.

Lastly , If everything above checks good and the board is changed and the unit produces a rapid flash then you could (temporarily) try wiring the furnace to an extension cord and plugging it into a receptacle within the home. After ensuring the L1 and N are correct once more, if this corrects the rapid flash then the issue is with the breaker feeding the furnace.

There will/can always be a “one in a million” situation but for the vast majority this guide will assist in finding the reason for the furnace rapid flash.

Schematic Reading Basics

Thu, 13 Oct 2022 16:39:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Schematic Reading Basics

For those new to the field, do you find it intimidating when you have to rely on the wiring schematic on a unit to figure out what a device is or what it should do? Or do you sometimes get confused looking at all the endless lines, weird symbols, and acronyms?

I’ll be first in line to tell you I shared those same feelings when I started my HVAC career. I am going to share some basics to reading Residential Wiring schematics with you in the article. The cool thing is almost all symbols are the same across all brands, and TYPICALLY the details within the symbols have a meaning, but every now and again the symbol will be generic and you will have to add in context clues to determine what they are.

Let’s dive right in… Typical Residential Carrier wirings diagrams resemble this:

June 10, 2026

Bryant only:

Bryant Service Technician

The Connection Diagram is best used when you need to know exactly where the high voltage wires are terminated, the Ladder form is best when trying to figure out how power flows from L1 to L2 through the devices- I have added two arrows to indicate L1 & L2.

Legend –ANYTIME you have an acronym (which is where a word or group of words are shortened into just a few letters) the full meaning can always be found here.

Notes – Periodically you will see “see note x” on a diagram, refer to this area for details pertaining to the area dictating the note.

Symbols

Okay, now let’s break down some common symbols:

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an O utdoor F an M otor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

Drawings in this article are from two Carrier manuals:25HNB9---2W & 50VR---07SI

This is a D e F rost T hermostat. This zig-zag line means temperature. TYPICALLY, if you look at the right bubble on limits: if the line lands on top then it means “close on drop and open on rise” and if it’s on the bottom then it would mean “close on rise and open on drop” Remember this!

This is a C rank C ase H eater- According to the description above: it will open on temperature rise.

Let’s add more to this same rule

Without looking up the acronyms I want to break these down.

Anytime you see these half circles they mean pressure. With this known, we can now see that the top switch will “open on pressure rise”- this is a High-Pressure Switch and the bottom will “open on pressure drop”- it is a Low-Pressure Switch.

Lastly, if you see a backwards “C” next to a straight line like is presented here, then it is a capacitor. Some drawings will rotate this symbol so it will then look like a “U” and a flat line. This particular one is a Start Capacitor.

Now, keep this basic knowledge memorized and build onto it. Take a look at the close-up diagrams below and look for the symbols we just discussed and see how they interact with the electrical system.

ABB VFD ACH580 Drive App

Thu, 13 Oct 2022 16:10:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

ABB VFD ACH580 Drive App

The ACH580 will be the new norm and it’s better to prepare now than later. With doing so, you will be familiar with its presence as well as it operation. The ACH580 ABB VFD’s have a regular keyboard which will need a kit to install the keypad behind plate. It comes with a standard and/or a Bluetooth keypad that can be purchased separately. With the Bluetooth keypad, you can use your phone to see vital information.

Link to Manuals that pertain to the ACH580

To use the Bluetooth, all you have to do is download and install the app for your phone to connect with the Bluetooth keypad. Then, you will have access to the drive information, firmware version, drive type, panel firmware, drive status, and last fault. It will show the fan condition of the main fan and the second fan as well. It will show motor usage in days and amount of time powered on.

Go to Play Store for Android or

Go to APP Store for Iphone

Type “Drivetune” in your search but without the quotation marks.

June 10, 2026

Drivetune App icon

QR Code for Sample Drive

Does the Defrost Board Have 24VAC?

Thu, 13 Oct 2022 15:57:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

Does the Defrost Board Have 24VAC?

The heat pump works in heating and cooling mode but it simply will not go into defrost mode.

Why won’t the heat pump go into defrost mode? I find this question quite often in the winter months after the tech has changed multiple defrost boards. This is a very simple problem to check and troubleshoot. Does the unit have 24VAC? Do not say yes because the unit will operate. Yes, the heat pump will work when the “R” or 24VAC is missing. The “R” powers the defrost circuit and the unit will run without it. Much like a straight cool unit, all that is needed to run is “Y” and “C”. Start by checking 24VAC at the defrost board on “C” and “R”.

I highly recommend using needle point leads so as not to damage the wiring harness. Start by checking 24VAC at the defrost board on the plug. 0VAC will be read when this problem occurs. I recommend starting here and working backwards towards the 24VAC source, for example, the transformer in the indoor unit. Working backwards will lead you to the source. This could include a broken wire under a wire nut or a broken thermostat wire. So, to recap, 0VAC between “C” and “R” = 0 defrost. The unit will run in both heating and cooling modes.

June 10, 2026

What We Have Here… is a Failure to Communicate!

Thu, 08 Sep 2022 14:09:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

What We Have Here… is a Failure to Communicate!

Have you ever found a communication fault or failure on an Infinity or Evolution system? Did you get a fault code 178 indoor coms fault or a 179 outdoor coms fault? Or have you seen a code 16 coming from the indoor board?

The cause of a communication failure could be a circuit board failed dragging down the com bus or the thermostat wire has failed. The thermostat wire may have high resistance in the wire causing coms loss or the wire has shorted killing the com volts.

This is how I explain to people in the field trouble shooting a 178/179 coms fault code.

Anytime we are checking the coms bus, we check A&B or green and yellow depending on how it is labeled.

Start by checking the communication volts on A&B or green and yellow on the green plug at the indoor board. Good coms volts are around 4VDC. If the volts are below 3.2VDC, you will see coms failure. If the coms volts are low, my next step is to check the volts at the board without any wires connected. Good coms volts on the board without thermostat wires should be 4.5VDC. If the coms volts are low coming out of the board, then the board is bad.

Next, I ask the tech to remove the wire for the outdoor unit leaving the thermostat connected to the indoor only and recheck coms volts. If the coms volts come up and the thermostat can communicate to the indoor unit, we will then know to check the thermostat wire going to the outdoor unit and the board for the outdoor unit. If the coms volts are still low then we need to check the thermostat or thermostat wire. I recommend checking coms volts on the thermostat base plate. Does the coms volts come back with the thermostat removed? If yes, then I recommend checking the ohm value on the thermostat. A trick we use in the field is taking the thermostat off the wall, attaching a short peace of thermostat wire, and connecting direct to the indoor unit.

Reconnect the wires after this step is completed.

Lastly, I ask the tech to remove the green plug from the outdoor unit board and check the coms volts on the green plug. Does the coms volts come back up or stay low? If the volts stay low, then most likely there is a wire problem and the wire needs checking. If the volts come back up, then we will check the board. I ask the tech to reattach the green plug, recheck coms volts, and see if the volts dropped. If yes, then we will proceed to check resistance on the board. Remove power to the unit and the green plug to ohm the board on A&B or green and yellow.

All of the communicating components may be checked by checking the ohms on A&B or green and yellow.

June 10, 2026

Testing Capacitors

Thu, 08 Sep 2022 13:56:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Testing Capacitors

First, let us start by saying there are a variety of capacitors in various shapes, sizes and colors. For the purpose of this article, we will just be talking about run capacitors, dual capacitors and I’ll offer a brief explanation of start capacitors. We will not go into how capacitors work because this is strictly for testing purposes only when you are out in the field.

Please, before ever attempting to do these procedures, be safety conscious about what you are doing. Always discharge the capacitors with a discharging tool, which can be found online. Never touch a capacitor until you have done so.

Capacitors

You might say: the system is running, so the capacitor must be good! That is not 100% true. Now let’s see why.

A capacitor has a voltage rating on it such as 370 vac or 440 vac. So, anytime you exchange it with a new one, make sure you get the voltage that matches or is greater than the one you are replacing. Also, remember to get the manufacturer rated capacitor for the motor. Do not replace with a different size microfarad.

Capacitors are used on motors to make them more efficient by increasing the RMS (Root Means Square) of the sine wave. Capacitors increase efficiency by taking the load off the windings and they have a range for tolerance. For example, a 5 microfarad capacitor with a +/- 5% tolerance means that 5-microfarad x .05 (which is 5%) = .25 tolerance. You can add 5 or subtract 5 and that will be your range. In this example, it would be a range of 4.75 to 5.25 microfarads. If you put your meter on microfarads and measure the capacitor from one side to the other and it reads 4.25 or 5.75, it will be out of range. This makes the motor less efficient and should be replaced. You should also check the new one as well because you can get one out of tolerance right out of the box.

Start capacitors are usually made of a composite material. They are usually black or brown but they can be other colors as well. They are rated in ranges such as 150 to 275 microfarads. That is how you can tell that they are start capacitors because they are only used for a moment to boost the starting of the compressor.

A run capacitor is in the circuit the entire time the motor is running. Typically, they are in a metallic shell and they come in various shapes. For example, it can be a round canister looking object or it can be oval looking cannister. Run capacitors can have either two or three terminals to put wires. Each terminal can take 1-4 wires. The capacitors with just two terminals are called run capacitors and the ones with 3 terminals are called dual capacitors. The only difference between single vs dual capacitors is that dual capacitors internally share one point – which they call “common”. The other two terminals are called herm and fan. Herm for the compressor and fan is for the fan.

June 10, 2026

Testing Without Power

As a reminder, you have to read the tolerances of the capacitors each time you use one and remember that some manufacturers make the plus and minus tolerances different. For example, some might have a tolerance of +10%/-5%.

When you test a dual capacitor, always remember to discharge it before continuing. You have to measure from the common to herm and the common to fan and determine the tolerance for both. This would be like testing two single capacitors but this one shares one terminal – the COMMON!

You may see μF on your meter or MFD. They both stand for “microfarad”. Learn your meter with no power before you learn with power. Again, safety first!

Testing With Power

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Remember this is live and to use extreme caution during this process!
In the picture, the top meter is measuring the amperage or amps of the herm wire which is the compressor side of the capacitor. The bottom multimeter is reading the voltage from the herm wire to the common. The formula to calculate microfarads is shown with values from the example.

MFD = (Amperage x 2652) / voltage

Simply measure the voltage from the herm to the common on the capacitor and write it down. Then measure the amperage of the herm wire coming from the capacitor to the compressor and write it down. Plug the numbers from your readings into the formula to find the microfarad reading.

38AUZ/D with Twin Furnaces

Thu, 08 Sep 2022 13:44:00 GMT

Anthony Coker

Technical Services Manager Southwest District

38AUZ/D with Twin Furnaces

One popular combination of Carrier equipment is twinning 2 residential furnaces together with a 6-10 ton commercial outdoor A/C unit. When this is done, it can get complicated very quickly because residential and commercial controls are different and yet they will have to be merged together for proper operation to occur.

What's different between Carrier residential controls VS Carrier commercial controls?

For the purpose of this article, the main difference is that on residential systems the transformer used to operate the system is located in the indoor unit whereas on commercial systems the transformer used for system operations is in the outdoor unit. With that being said, this combination has two furnaces each with their own transformer as well as the commercial outdoor unit with its own transformer. This gives us a total of at least 3 transformers.

On commercial buildings, it is not as simple as combining all the R (24v) wires because these buildings typically have 3 phase power. With three different incoming power combinations for the three transformers, there is a good chance that the transformers will not be “in phase”. Yes, there is phasing on low voltage 24 too (not to be discussed in this article) …. If the transformers are out of phase then R to R on two different transformers will read roughly 45vac when it should be 0vac.

So, what is the solution to this dilemma?

1st, Plan ahead- determine how the system will be controlled for furnace operation. This will be critical to the thermostat setup. The options are A) single stage furnaces acting as two stages, B) single stage furnaces acting as one single stage unit, C) two stage furnaces setup for “adaptive” heating or setup to operate traditionally with W1 & W2 inputs.

2nd, Install twinning kit- use an approved twinning kit to tie the furnaces together. When the twinning kit is installed there will need to be a “main” and a “secondary” furnace setup. These kits can be installed differently Depending on the selection from the first step. (please follow the installation directions for the appropriate twinning kit)

3rd, Install relays- there are wiring diagrams with the twinning kits for wiring residential outdoor units. Since the Carrier commercial units have their own transformers, the wiring will be slightly different. The best way (recommended way) is to utilize isolation relays to ensure that the two different low voltages (furnace vs outdoor unit) never cross paths.

Wiring the outdoor unit

The twinning kit should be used to determine how to wire the furnaces so I did not show wires for the heat side. I want to show clarity on the outdoor unit alone. Please take a look at the way the relays are used to separate the two different control voltages.

June 10, 2026

Bryant only:

Bryant Service Technician

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an O utdoor F an M otor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

The Infamous E1: Part 2

Tue, 09 Aug 2022 14:15:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

The Infamous E1: Part 2

E1 fault code on Ductless equipment is communication fault between the indoor and outdoor units.

When the E1 code shows up on the indoor display board, the coms have failed and the systems have stopped working. Until this problem is fixed, the system will remain off.

Start trouble shooting this problem at the outdoor by taking a DCV reading on L2 and S or 2 and 3 depending on how the unit is labeled. Take a DCV reading on the terminals for the indoor unit wires.

Good coms volts look like + to – 50 volts fluctuation.

If you see a fixed negative or a small amount of fluctuating volts staying in the negative, the indoor board has failed. If you see a fixed positive volt reading or a fluctuating positive reading the outdoor board is bad.

The reactor also needs to be checked. Check the reactor with the wires off and ohm it out. The ohm reading should be .1-1 ohm and should not be grounded.

June 10, 2026

Common Explained

Tue, 09 Aug 2022 14:04:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Common Explained

When you’re still green with experience or if you just entered an HVAC apprenticeship, there will be terms or sayings that you will not understand. One of these things will be the term “common” when discussing wiring. I’m going to cover what common is and give examples.

The word Common in the HVAC field is used everywhere, it can be almost anything. Almost every electrical device has a common. Common for each device is the same BUT its meaning is only local. What I mean by that is: the definition for what “common” is, changes with each item or device.

Confused yet? Let’s break down some items within the system for a better understanding:

Single Phase Motors & Capacitor

June 10, 2026

Bryant only:

Bryant Service Technician

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an O utdoor F an M otor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

*Wiring diagrams highlighted with colors chosen for high contrast- not for wire color designation*

For the motors, I have highlighted the L1 & L2 power wires through a basic Carrier 25HCB condenser unit as they feed the compressor and condenser fan motors. The fan motor’s terminals are not labeled but are the same as the compressor’s. I circled the “commons” in purple. For the motors, there are two windings within the motors: Run to C and Start to C . The two windings come together at a “common” terminal as this meeting spot is what they both have in common.

For the capacitor in the center—the capacitor has one input and two outputs. One is (F)Fan and the other is (H)Hermetic (compressor). These two outputs have the same terminal for their input- common.

Relay Contacts

Relay contact terminals are labeled (C) Common, (NO) Normally Open, (NC) Normally Closed. When the relay is not energized C will be closed to NC and C open to NO. When the relay is energized, both will be reversed. Now it will be C closed to NO and C open to NC. Each terminal (NO & NC) have a relatable contact: (C) Common.

Catching on? Let’s discuss a more complicated “Common”:

Carrier Residential Packaged Unit Low Voltage

*Wiring diagrams highlighted with colors chosen for high contrast- not for wire color designation*

Low voltage starts in the red box at the transformer, 24vac goes to the Indoor Fan Board (IFB), through a fuse and on to the thermostat. Depending on what the thermostat calls for, 24vac will be sent down a different wire(s) to turn on/off the multiple devices in the system. The other low voltage wire (C) has an unbroken path to EVERY component in the unit. I have highlighted the pathway in blue and circled each component in purple. This wire/path is something each device has in “common”—it is the common wire. In layman’s terms, the common wire is the return pathway for voltage to come back to the transformer since it left out on the 24vac side.

The Common wire/terminal is always the one thing that is relatable or in common with the surrounding wires/terminals. Relays, motors, control boards, and even transformers all have some type of common wire/terminal. Common for a relay isn’t the same as common on a motor, but within each given device they carry the same meaning. Now go back and reread the second paragraph above—it will have a deeper meaning now.

Challenge: Check out the high voltage side of the Transformer. It has a COM terminal…. it’s not low voltage common. What is it?

That’s all.

Soldering, Brazing, and Welding

Wed, 06 Jul 2022 16:47:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Soldering, Brazing, and Welding

In this article, we will go over a few differences between the types of metal-joining processes used to connect pipes together. Without these processes, we would not be able to move refrigerant to any components such as steel pipes on a chiller or copper pipes on a residential air conditioner. We may have to make field modifications to attach them together in the field or just to replace an item such as an evaporator coil. That is why it is important to know the various techniques used in today’s industry. Remember: safety is first and foremost. Always wear safety glasses or a face shield when brazing or soldering. Gloves should always be worn to protect your hands. If you are in a confined area where there are a lot of fumes or smoke, then use a respirator.

Soldering

Soldering is the process of joining two pieces of metal together. You will need solder, flux and a heat source for soft solder. For this example, we can use a propane torch. This is what a lot of plumbers use to plumb your house for water.

You will need to clean both pipes on the outside ends and deburr the inside of them to make sure there are no objects that can break free in the pipe and cause clogging or issues with the operation of the refrigerant cycle. Now we clean the inside of the fittings as well, typically using an emery cloth or sand paper. After cleaning all surfaces by sanding, you will want to wipe them with a cloth to remove any residual debris. Then, you will need to put the flux on the areas you cleaned and connect them together with the coupling. Now that they are together we can solder them.

Flux paste cleans and assists in the bonding of the solder to the pipes. When you solder you will need to heat the fitting in the middle as to draw the solder into the fitting. The fitting has to be hotter than the pipe. If they are the same temperature, the solder will not flow inside or wick into the fitting between the pipe and the fitting; it will just drip onto the ground. If that is the case, cool the pipe down with a rag that has been wet with water and then try again until it is right.

Applications for solder are as follows: Refrigerant lines that will not exceed around approximately 200psi when using 50/50, which is 50% tin and 50% lead. This will work for low pressure refrigerant and non-potable water (not drinkable).

95/5 solder is 95% tin and 5 percent antimony and can be used for drinking water applications. 95/5 is stronger as well for HVACR applications which can handle pressures up about 275psi. Now there is a lot more involved than this. This is just an informative view. Other variables include pipe strengths, tensile strengths and types of copper you are using. “Example: type k, l or m which is a rating of copper pipe for wall thickness changes the maximum pressure each can handle. The lowest of the three is M and the highest is K. But it even has an annealed version and a drawn which changes the pressures as well.

June 10, 2026

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

It consists of two similar metals or dissimilar metals being joined by a brazing rod that melts before the metal being joined will. This will help assist in the bonding process. You can butt the two pieces together and braze them and it will be stronger than a soldered joint. The copper pipes can get red and silver solder will already be melted at this point.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid. Solidus temperature is the highest temperature at which the metal is completely solid.

The temperature at which metal melts is called its melting point.

Brazing uses a higher temperature to melt the rods than soldering. Gas torches such as MAPP gas or oxy acetylene could be used depending on the environment and the size of pipe. MAPP gas works well in non-windy areas for up to ¾ inch pipe. Anything larger than that would push the limits of the heat.

In brazing, the components that make up the rods is determined by the metals you want to join. For the HVACR industry, we typically use silver solder containing different percentages of silver. This will determine the fluidity of the rod on the metal being joined, the cleanliness of the joint for aesthetics, and the strength of the joint.

Flux can come in various forms such as a paste or a coating on the rods. In the example for the HVACR purposes we will use 15% silver solder. An example composition of 15% Silver Solder is: 15% Silver, 80% Copper, 5% Phosphorous. In joining copper to copper, none of these phosphorus/silver/copper rods need flux or would even benefit from it. The phosphorus allows the rod to self-flux on copper. So, if you use the silver solder it has phosphorus in it and does not need flux. It is the flux!

Example: Two pipes cleaned and placed inside a coupling. Heat the pipes until the 15 percent silver solder melts and spreads smoothly along the metal joint between the pipe and the coupling. Then do the other pipe at the joint at the coupling as well. Then stop and allow to cool. Or use a wet rag to cool it down.

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Welding

Welding is the process of melting the two metals together and is the strongest of all joints. It can be used on various metals and there are several processes that go along with this as well but we will stay within the HVACR industry needs.

Welding comes in various forms such as MiG, TIG and Stick Welding. There are others but these are the main ones.

MIG is a form of wire welding. TIG is a form of a high frequency welding which melts the metals together or melts the filler rod to the metal to fill the void between the two pieces of metal. Stick welding uses a flux coated rod that comes in contact with a grounding clamp from high current. It produces an arc, which starts the melting process of the fluxed filler rod in the midst of the two pieces of metal.

In the HVACR industry steel pipes are used for industrial equipment with large pipes such as chillers. The pipes are welded together at the factory but if there was ever a leak in one you would have to weld it. Not your typical daily function, but it can be done. It is probably the least used metal-joining process from a technician’s point of view but it is still used.

The Infamous E1: Part 1

Wed, 06 Jul 2022 15:25:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

The Infamous E1: Part 1

First, what is an E1 fault code? E1 is a ductless system communication fault between the indoor and outdoor units. Are you having a nuisance E1 after you replaced the circuit boards? Did you retro fit a ductless system using the existing wire and line set and received the infamous E1?

E1 from an induced voltage will cause communication problems with your new ductless system whether it is a brand new install or a retro fit change out. The problem is the wires inside the sheathing are twisted together causing an induced voltage on the “S” wire or signal wire. A 20 VAC and above will kill or scramble the signal causing a communication fault between the indoor and outdoor unit.

The way we check for this is to turn power off to the system, disconnect the “S” wire or the number “3” wire from both units. You may see the “S” wire or the number “3” wire depending on how the unit was labeled. Make sure the “S” wire does not touch anything when disconnected! Then turn power back on. I want to ensure you are cautious and aware: you are working on LIVE equipment! Set your multimeter to Volts AC with an alligator clip on one lead connected to the “S” wire and the other lead to ground; measure the induced current. It is preferred the reading is 0 volts, however, anything under 20VAC is acceptable. This problem has occurred due to using the wrong type 14/4 wire as well as using 18/8 wire. The use of the 18/8 wire is incorrect and dangerous!

The way to correct this problem is by replacing the indoor unit wire with the correct 14/4 wire. It is recommend using Duckt-strip brand wire due to its flat 4-wire design. Also, the Duckt-strip will not self-induce voltage into the “S” wire. Something to remember when installing a ductless product: it is best not to run the wire next to other high voltage wires. This can cause an induced voltage as well.

June 10, 2026

What’s Your Resistance?

Wed, 06 Jul 2022 15:06:00 GMT

Anthony Coker

Technical Services Manager Southwest District

What's Your Resistance?

When assisting with field calls, I ask this question in reference to electrical devices several times a day. The answers that I receive back ranges from: 75, none, a lot, nothing, 237K, and many more. I would like to help you better understand what you are checking and how to “read” it.

Electricity wants to flow! This is a fact. What keeps electricity from flowing? Resistance. Resistance is a force that opposes the flow of electricity and is measured in Ohms. The symbol for Ohms looks like an upside down “U”. When checking resistance there are no negative numbers. It starts at Zero and goes up from there and goes into the millions.

Whatever you are checking, whether it’s compressor windings, relay contacts, reversing valve coil, etc. if the meter reads 0.0 then this means electricity can flow with absolutely no trouble where as OL means the opposite that electricity will not flow at all. I recommend checking your meter for integrity periodically. This can be done by putting your leads together. This test should result in 0.0. Anything above 0.0 should be added to your reading when testing something. If the meter is reflecting anything higher than one or two ohms then the test leads and/or battery should be replaced. This ensures your readings are accurate.

Sometimes the meter will not show a number but instead “OL”; this represents Open Line which more or less mean infinite ohms. OL can be tricky, though, because the meter being used will show “OL” when the resistance being checked is higher than the meter can check. For example, if a meter that is rated for 100 ohms is used to check something that is 120 ohms this meter will show OL.

June 10, 2026

Bryant only:

Bryant Service Technician

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an O utdoor F an M otor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

With all these possible large numbers it is impossible to put them on a meter’s tiny screen. To make the numbers fit, abbreviations have been made. K for Thousands and M for Mega. Mega means million. Things get misdiagnosed due to the two mentioned letters being overlooked. If a meter reads 1.1, 1.1 K, or 1.1 M these are not the same thing. The first is literally 1.1 and the second is 1,100 and the last being 1,100,000. For example, let’s say you’re reading a compressor’s resistance to ground and you are looking for it to be greater than 2 million. If you misread 2.1M for simply 2.1, then you have misdiagnosed the compressor as being grounded.

Some meters are auto ranging, meaning you simply put it on resistance and take your reading. If the meter is equipped with a “Range” button then you likely have to select which range you want to check. As you push the range button it will move the decimal which allows for different number arrangements. Each meter should be looked at individually for the exact specs but as an example the meter may start with 60 ohms range so anything over 60 would show OL. Pressing the range button one time changes it to 6,000. Here is an example from fluke

Range values

600.0 Ω
6.000 kΩ
60.00 kΩ
600.0 kΩ
6.000 MΩ
60.00 MΩ

If there’s resistances there’s an ohm value. Get out there and ohm something out!

CADM Fault Code 3

Thu, 02 Jun 2022 15:22:00 GMT

Anthony Coker

Technical Services Manager Gulf Coast District

CADM Fault Code 3

What is fault code 3 on the Comfort Alert Diagnostic Module (CADM) and why am I getting nuisance trips?

CADM Fault code 3 is a short cycle alarm and lock out meaning the system did not run for a minimum of 3 minutes. This could be due to a no load or low load application, like a church. When no one is occupying the building, the system ran in cooling mode for under 3 minutes then cycled off. This has to happen four consecutive times, then the CADM will lock out on fault code 3. To reset the fault you simply power cycle the outdoor unit.

If you are receiving a code 3 and it is not from a lack of run time, then you need to look into a possible charge problem or blower problem.

This information can be located in the installation manual that comes with the unit. This is the definition from the install manual:

Yellow “ALERT” Flash Code 3 Short Cycling Compressor is running only briefly (four consecutive cycles of less than three minutes each) LOCKOUT 1. If low pressure switch is open: a. Low refrigerant charge b. Evaporator blower is not running c. Evaporator coil is frozen d. Faulty metering device e. Condenser coil is dirty f. Liquid line restriction (filter drier blocked if present) 2. If high-pressure switch is open, go to Flash Code 2 information 3. Intermittent thermostat demand signal four. System or control board defective.

The system needs a minimum run time for oil return. The way we fix this is with the correct type of thermostat.

I recommend two different thermostats for this application to help resolve fault code 3 due to short cycle.

Carrier Part Numbers 33CS2PPRH-03 and 33CS2PP2S-03 commercial thermostats with built in 3 minute minimum on time.
PRO1 T855 is a commercial programmable thermostat. You have to enable this feature and I recommend setting to a minimum of 5 minutes.

By using one of these thermostats, with a minimum on or run time, fault code 3 short cycle problem will go away.

June 10, 2026

Condensate Pump Replacement

Thu, 02 Jun 2022 14:33:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Condensate Pump Replacement

We are finding ourselves with more and more VRF components that will require maintenance periodically. Example: a 40VMF

Below are the procedures of handling one of the components mentioned above. As always, please take your time and use precautions in all work you perform.

12 Steps to replace a Condensate Pump on a 40VMF

1) This is the location of the condensate pump in relation to the control compartment

Step 1

2) Remove all screws from the four corners indicated by the arrows

Step 2

3) Remove the 3 screws to remove wire routing cover.

Step 3

4) Remove the felt tape covering the wire route

Step 4

5) Trace the pump high voltage wiring harness to the control compartment

Step 5

6) Unplug the 2 black wire connectors from the pump connector on the control board and unscrew the green ground wire from the control compartment

Step 6

7) Trace out the pump float alarm cable. Notice that it runs under the control compartment and will require taking the control compartment screws out. Let it hang down so you can access the wire all the way over to the wire bundle on the right side of the control compartment.

Step 7

8) To remove the control compartment first cut the wire tie holding the wire bundle together.

Step 8

9) Next unplug the red and black 2 wire plug from the water connector on the control board

Step 9

10) Once you have both cables disconnected remove them from the wire route in the bottom of the foam drain pan.

Step 10

11) Next you pull the drain pan down about 2 to 3 inches all the way around the unit. You will then be able to pull the condensate pump side down about 10 inches.

Step 11

12) You will then be able to access the pump Assembly which can now be removed by removing the 3 mounting screws.

Step 12

To complete the replacement, install the new condensate pump assembly and reverse the previous steps.

June 10, 2026

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid. Solidus temperature is the highest temperature at which the metal is completely solid.

The temperature at which metal melts is called its melting point.

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Alerts vs Alarms on the Comfort Link

Thu, 02 Jun 2022 13:24:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Alerts vs Alarms on the Comfort Link

Disclaimer- This article does not detail on how to reset alarms because a previous article was done on this already. You can view that article here .

When using the comfort link to check out alarms and alerts you might wonder: is there a difference or are they the same? Which one shuts down the whole unit and which one will leave it running or partially running? I will get into that here and clear up some of the confusion with how the Comfort Link controller dictates all of this.

There is a difference with alerts and alarms. In the controls manual it defines these as follows:

T — Alert: Part of the unit is down, but the unit is still partially able to provide cooling or heating.
A — Alarm: The unit is down and is unable to provide cooling or heating.

June 10, 2026

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid. Solidus temperature is the highest temperature at which the metal is completely solid.

The temperature at which metal melts is called its melting point.

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Let’s start with the alert or code that begins with the letter T. Usually, this is not a full shut down alert code. In this mode the circuit with the problem code will not run and the secondary circuit takes the lead and attempts to condition the space. So, if you were to check alarm history you would see alerts starting with a T for a specific circuit depending on how many are available to the unit.

Now let’s go over when the Comfort Link controller has an alarm light indicated on the unit. It is in an alarm state and will not run without technician intervention. The controller has to be reset and the responsibility falls on the technician to troubleshoot the issue.

Where do alerts or alarms start? In the manual it states they start as pre-alerts. This is defined below :

P — Pre-Alert: Part of the unit is temporarily down. The alarm is not broadcast on the CCN network. The alarm relay is not energized. After an allowable number of retries, if the function does not recover, the pre-alert will be upgraded to an alert or an alarm

For both alerts and alarms they start out as pre-alerts. They get upgraded after a certain amount of startup has been tried. These usually follow a three-strike system or something similar. On the third start if the issue persists it will either go into alert or alarm depending on what it is.

Depending on what code the unit is indicating it can lead you in the right direction. Confirm the controls manual when you can to ensure that the right error code is being defined. Not all Comfort Link manuals are the same nor alarm and alert codes are the same. Each unit differs.

HVAC Safety

Mon, 02 May 2022 14:26:00 GMT

Anthony Coker

Technical Services Manager Southeast District

HVAC Safety

June 10, 2026

Safety is something we should think about and practice in almost everything we do. We get comfortable in our everyday lives and don’t think of the dangers in doing the work that we are accustomed to doing or paid to do. For example, just picking up a box off the floor to put it on a counter could injure your back. Let’s look at and review some of the safety equipment and procedures used by HVAC technicians. Before we get started, I’d like to remind you that only trained and qualified persons should service or install HVAC equipment. On the job safety is your responsibility to keep you and others around you safe. Also, the information given here is general in nature and not to be used as a substitution for the manufacturer’s instructions.

A lot of on the job injuries happen because personal protective equipment is not used. Here is a list of common personal safety equipment: a Hard Hat to protect your head, Safety Glasses or Goggles to protect your eyes, Gloves to protect from burns, chemicals, cuts, etc. Ear Plugs, Safety Shoes, and Safety Harness or Lanyard, just to name a few. Safety equipment needs to be taken care of inspected often and used properly.

When working on HVAC equipment with the electricity turned on, we should remember to remove rings, watches, bracelets, etc. that are metal that could come in contact with electrical components that could cause electrical shocks and burns. An HVAC technician will work with equipment that will have AC voltage that ranges from 24v to 575v. With the new inverter equipment, there is DC voltage ranging from 5v to over 300v. So, remember to always observe the safety tags and labels on the equipment and the instructions. When working on the equipment, LOCK OUT / TAGOUT the disconnect or electrical panel to make persons aware that the equipment is being worked on. Never take for granted that the equipment does not have electricity; always use a meter to verify it.

Safety is used to keep you and others from injury or death. Please follow a manufacturer’s instructions and instructions that come with the safety equipment. We will discuss next time safety around refrigerant and pressurized gases that are used in the HVAC industry.

Sources:

HVAC Servicing Procedures

Safety labels from:

safetyculture.com ( PPE )

The Unknown Soldier

Mon, 02 May 2022 14:12:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

The Unknown Soldier

Wondering why the VFD is called the Unknown Soldier? It is because it does a lot of work and goes unrecognized. It is one of those things that does its work behind the scenes and doesn’t get recognized until it stops working. Well we are going to give the recognition to this one and maybe by doing so it will have a long and productive life!

VFD

Maintenance of the VFD is critical and can be detrimental when not maintained at specified intervals. The dust can cause overheating and possible damage to the VFD as well causing a shortened life span to the device.

All this information can be found on HVAC Partners under VFD-08SI

VFD Maintenance

If installed in an appropriate environment, the VFD requires very little maintenance.

Table 1 lists the routine maintenance intervals recommended by Carrier

June 10, 2026

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid. Solidus temperature is the highest temperature at which the metal is completely solid.

The temperature at which metal melts is called its melting point.

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Table 1 - Maintenance Intervals

Heat Sink Cleaning

The heat sink fins accumulate dust from the cooling air. Check the heat sink annually and if the dust is heaver than usual increase the frequently of cleaning.

Use the following procedure to clean the heat sink on the (AHC550 VFD)

1. Turn off power and (lock out/tag out) unit for your safety and others.

2. To remove the drive cover. Remove the captive screw. (See Figure 1)

Figure 1 – Remove Cover on the (ACH550 VFD)

3. Press together the retaining clips on the top cover and lift. (See Figure 2)

Figure 2 – Remove Cover on the (ACH550 VFD)

4. Blow clean compressed air (not humid) or dry nitrogen from bottom to top while simultaneously using a vacuum cleaner at the air outlet to recover the dust.

5. Replace the cooling fan.

6. Replace the drive cover.

7. Restore power.

Use the following procedure to clean the heat sink on (ACS320 VFD)

1. Turn off power and (lock out/tag out) unit.
2. To release the top cover, insert a small straight blade screwdriver into the slot and press it in to release. (See Figure 3)

3. Blow clean compressed air (not humid air) or dry nitrogen from top of ACS320 while simultaneously using a vacuum cleaner at the base to recover the dust.

4. Replace the top cover.

5. Restore power.

Figure 3– Remove Cover on the (ACS320 VFD)

Using the Navigator Tool

Thu, 28 Apr 2022 14:23:00 GMT

Anthony Coker

Technical Services Manager North Georgia District

Using The Navigator Tool

The Comfort Link Navigator is a great option for Comfort link products with faulty or non-responsive controllers. A lot of times the sun will fade the screens and you can’t see the LED readouts. The control buttons will also fail and get stuck so you can’t control anything.

So how do we fix these issues?

That’s where the Navigator comes in. You can do all of the same functions as the Comfort Link controller with a plus. It has a four-line read out screen. You can still force certain points on or off with the same authority as the Comfort link. It is universal so you can plug it into any Comfort Link with confidence.

June 10, 2026

Brazing

Brazing is the process of joining two metals together without the wick effect that solder has.

Now a few other terms we must be aware of:

Liquidous temperature is the lowest temperature at which a metal is liquid. Solidus temperature is the highest temperature at which the metal is completely solid.

The temperature at which metal melts is called its melting point.

Round 2 terminal capacitor

Round 3 Terminal Dual Capacitor

Oval Capacitor

Oval Dual Capacitor

Start Capacitor - Black

Start Capacitor - Brown

Part Number 30GT-911---062

Setting Up the Navigator

Only plug into the LEN port, do not plug into the CCN because it could damage the hand-held unit.

On every Comfort Link product there are two modular telephone style (RJ14) connector. They are labelled LEN which is Local Access Network. The other is labelled CCN which is Carrier Comfort Network. You will plug into the LEN port of the unit. All the power and data are done through the one LEN jack. No batteries or chargers are needed. It is a self-contained unit. It is also equipped with two large magnets on the back to ensure it stays on the unit while you are using it.

Accessing the LEN Ports

On some units, you can access the LEN port through means other than opening the electrical cabinet. See table below for locations:

Once you have located the plug locations and connected to the LEN port, the Navigator tool will start up.

You can use all the same functions as the Comfort Link controller mounted to the unit. However, with the Navigator tool, you have more than one read out screen, and no longer have to press escape and enter for every screen. Your local Mingledorff’s will be able to help you find one if you decide to purchase one.

Source: All information came from Form 30/48/50-6SI Installation Instructions

M#25VNA8 Troubleshooting Tips

Thu, 07 Apr 2022 16:25:00 GMT

Anthony Coker

Technical Services Manager Southeast District

M#25VNA8 Troubleshooting Tips

June 10, 2026

The M#25VNA8 communicating unit has several devices that aid in the operation and protection of the unit. These devices are the suction pressure transducer, outdoor coil thermistor, outdoor air thermistor, suction thermistor, and the discharge thermistor. Sometimes these devices can start to fail, but not completely fail. When this happens the M#25VNA8 unit tries to correct the operations or protect itself with the info it is receiving from these devices. The info the unit receives can cause the unit to shut down on a safety or run inefficiently.

The suction pressure transducer allows the unit to monitor low pressure cut-out, loss of refrigerant charge, compressor protection, lubrication and oil circulation. It also aids in the control of the electronic expansion valve in the heating mode. The outdoor coil thermistor provides the outdoor coil’s liquid line temperature to the heat pump board in order to allow the unit to operate in the low ambient operation, defrost initiation, and defrost termination, with the assistance of the outdoor air thermistor. The suction thermistor is used to assist with the control of the electronic expansion valve and monitor the suction line temperature to the compressor. The discharge thermistor is used for protection against over temperature of the compressor. Now that we have a description of what the devices do and assist within the unit, we can look at ways to check and determine if the devices are defective and causing problems.

The suction pressure transducer receives 5 volts DC to it and sends 0 to 5 volts DC back to the control board, which is interpreted into pressure. At the connector on the control board, you can confirm that the suction transducer is receiving the 5 vdc on the ground pin and the supply pin. There is a formula that you can use once you read the output voltage between the ground pin and output pin on the control board. A formula is used to calculate the DC voltage in to pressure. You can also use the graph in the service manual. Once you get the pressure from the graph or formula, compare these calculations to your refrigerant gauge readings and compare for accuracy.

Pressure DC Voltage Formula

For example, if the measured output voltage is 3.0 VDC & Pressure is 50 psig:

50 X (3.0 — 0.5) — 50 X 2.5 = 125 psig.

The temperature thermistors are electronic devices which sense temperature. You can check these thermistors with an ohm meter. As the temperature increases, the resistance of the thermistor decreases. The outdoor air, outdoor coil, and suction thermistor are all 10K ohm thermistors. There is a graph that is in the service manual to compare the resistance of the thermistor to temperature. See below.

The discharge thermistor is a 50K ohm thermistor, which also has a graph that is in the service manual to compare the resistance of the thermistor to temperature also. See below.

There is one other way to check the accuracy of these devices. With a communicating wall control, you can go into the service information of the wall control and look at the system while it is in off mode. After the unit has been idle for about 20 minutes, you can compare all the thermistors readings to each other. The readings will be close if there are no failing thermistors. The discharge thermistor can read a little higher due to the heat from the compressor if it was previously running, or the sump heater was on. While the unit is still off, or if it is running, you can compare the unit pressure from your gauges to the reading on the wall control while still in the service info screen.

The info discussed from the service manual is to get a more accurate picture of the device that may be in question, but use the communicating wall control for a quick reference if these devices are in question. With a little understanding of what a device does in a unit, it can help determine why the unit is not operating efficiently or shutting down on a safety.

Sources: Service Manuals For

25VNA8 Infinity 18VS Variable Speed Heat Pump

24VNA9 Infinity 19VS Variable Speed Air Conditioner with Puron Refrigerant

288BNV EVOLUTION V VARIABLE SPEED HEAT PUMP

189BNV EVOLUTION V VARIABLE SPEED AIR CONDITIONER

WITH PURON REFRIGERANT

Ductless Line Set Sizing

Thu, 07 Apr 2022 16:14:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Ductless Line Set Sizing

When installing Carrier/Bryant Ductless (mini splits) units please refer to the installation manual for the particular model of the unit you are installing or servicing. If you don’t have the needed manuals, they can be found on HVACPartners.com where you can also register for an account. You can also reach out to a Mingledorffs Technical Service Manager who would be glad to send them to you.

I will be referencing charts or tables from the manuals. In older literature, it is under “System Requirements”. In newer literature, it is under installation titled “Refrigerant Piping.” On multiport units it is under “Piping Requirements.”

Indoor and outdoor manuals should always refer to the same pipe diameters needed but, in the event that they differ, please refer to the install manual of the indoor unit when determining the lineset pipe sizing.

BEFORE installing a ductless unit, the information discussed in this article should be taken into consideration to ensure that the parameters are followed. If the wrong size lineset (according to the manual) is installed then then our recommendation would be to replace with the correct size.

June 10, 2026

Bryant only:

Bryant Service Technician

This symbol is for an equipment ground- almost any time you see three lines parallel either horizontally or vertically- they will mean earth/ ground.

Here is an O utdoor F an M otor where you can see it contains two windings, Start and Run. Also, in green is another symbol for ground

Pulled from an indoor ceiling cassette 40MBCQ

The chart/table on outdoor units have loads more of information so I will assist in clarifying.

*to keep things simple, we typically round close decimal numbers*

Min. Piping Length- This is the minimum allowed amount of lineset. Nothing less than 10 Feet.

Standard Piping Length- this is how much lineset the unit is precharged to handle. Do not remove charge to compensate for linesets that are shorter than 25 feet.

Max. outdoor-indoor height difference- how far you can separate the indoor from the outdoor vertically, two labels are show- IU indoor unit above OU outdoor unit and vice versa.

Total Maximum Piping- this is the maximum allowed pipe length. Installations beyond this lineset length will not be approved nor recommended.

Additional refrigerant charge- if your lineset is over 25 feet but not longer than the MAX, this is how many ounces per foot should be added to the unit for proper operation.

Suction Pipe- the suction hookup size at the outdoor unit.

Charge amount- how much charge the unit has from factory to cover 25ft of lineset.

Pulled from an outdoor heatpump model 38MARB

Pulled from Multiport outdoor unit 38MGR

These units are more complex and have more variables to consider.

*to keep things simple, we typically round close decimal numbers*

Min. Piping Length per each indoor unit- This is the minimum allowed amount of lineset for each indoor unit

Standard Piping Length per each indoor unit- this is the amount of lineset that has been “reserved” for each indoor unit for refrigerant charge purposes.

Max. outdoor-indoor height difference- how far you can separate the indoor from the outdoor vertically. Two labels are shown- IU indoor unit above OU outdoor unit and vice versa.

Max. height different between indoor units- if the indoor units are on different levels, then they should not exceed this amount of vertical separation amongst themselves.

Max. Length per each indoor unit- no indoor unit should have a lineset longer than this number. Do not exceed this number for any indoor unit lineset.

Max. Piping Length with no additional refrigerant charge- add together all of the lineset lengths for all the indoor units. If your lengths are above this number, then additional charge is needed.

Total Maximum Piping Length per system– when adding together all the indoor pipe lengths, this is the total length that the unit can support. Pipe lengths greater than this are not approved nor recommended.

Additional refrigerant charge- if your total lineset length is over the “Max. Piping Length with no additional refrigerant charge” amount, this is how many ounces per foot should be added to the unit for proper operation.

Pipe sizes: these show the pipe sizes with an asterisk (*) and then the quantity of those ports.

For example: from the 36K– 1/2 *2+3/8*2

This means 2 at ½ and 2 at 3/8.

In the event that the correct line set size is ran and it is not the same size as the hookup of this unit, use the factory supplied adapters to make the connections.

HVH8 Compressor Troubleshooting

Thu, 07 Apr 2022 13:51:00 GMT

Anthony Coker

Technical Services Manager North Alabama District

HVH8 Compressor Troubleshooting

The HVH8 compressor operates with 3-phase variable frequency Pulse Width Modulation (PWM). To troubleshoot a fault related to the code use the following steps.

1. Disconnect compressor power leads from the inverter (MOC Board) terminals, U (Yellow), V (Red), and W (Black).

2. Measure the resistance between yellow to red, yellow to black, and red to black. Then check the values with table 7 in the installation book. Each value should be equal.

June 10, 2026

3. Measure the resistance to ground for each lead.

4. If the resistance checks out, reconnect power leads to appropriate terminals.

5. If the resistance appears to be abnormal, it will be necessary to measure the resistance at the compressors fusite terminals.

6. During the removal of the compressor fusite cap, do not remove the RTV sealant. Remove the harness plug, measure resistances, and compare to table 7.

7. Special care will need to be taken with the replacement of the compressor fusite cap. Make sure the two holes in the compressor fusite terminal box are still full of RTV sealant before the cap is reinstalled. The factory RTV can be reused as long as none of it has been removed during the cap removal.

8. Reinstall compressor sound blanket making sure the discharge thermistor and compressor power harness are routed as they were from the factory.

Isolating the Problem in The Unit

Thu, 10 Mar 2022 16:58:00 GMT

Anthony Coker

Technical Services Manager Southeast District

Isolating the Problem in The Unit

June 10, 2026

There are many ways to diagnose problems with a unit. You can listen to the customer describe the operations of the unit, and you can observe the operations for yourself. Then comes the time when you have to get your tools and meters to start checking why some parts of the unit are working, or why nothing is working.

One way of checking out why a motor or compressor is not working is the Hopscotch Troubleshooting Method. Hopscotching is a way of testing for voltage readings across components in the circuit that is not working. You would place one meter lead on one side of the unit’s line voltage or control voltage, depending on what was not working. For example, let’s say the motor is not running: place one meter lead on one side L2 going to the motor, then you would take the other meter lead and put it on L1 going to the motor before any components that this wire would connect to. Let’s say your voltage is 230v at this point, as you move your meter lead that is on L1 to the next place (the other side of a contactor or relay switch) leaving the other meter lead on the L2 and not moving it. This is how you hopscotch through to the controls to the part that is not working. When the meter lead that is testing the L1 side does not read 230v, that is where the problem is.

There may be burnt out points on a contactor, and/or the relay switch didn’t close due to being stuck open. If you had 230v at the motor, you probably have a motor that failed, but the process of hopscotching confirmed that there were no problems with the controls before the motor. The same process can be used to check the control voltage that turns on the components.

This is just one way to isolate problems with components within the equipment. You can use the hopscotch method in troubleshooting resistive loads like crankcase heaters or heater elements, as well as inductive loads such as relay coils, solenoid coils, and transformers. It can also be used to check switch contacts as in low/high pressure switches, contactors or relays, etc. This method allows you to check the complete circuit from start to the end.

Sources:

HVAC SERVICING PROCEDURES

Ecobee 5 Setup for 2 stage with Dehum

Thu, 10 Mar 2022 16:58:00 GMT

Anthony Coker

Technical Services Manager Southwest District

Ecobee 5 Setup for 2 stage with Dehum

One of the most popular combinations right now is the FV4 air handler with a 2 stage outdoor unit with a/c driven dehumidification. This combination is an awesome thing when it is adequately setup. When this system is installed and it is not setup or wired correctly it will not pull moisture from the home but instead cause the home to have higher humidity. I have made a guide to walk you through setup up and wiring this system to allow the homeowner to reap all of the benefits their system is capable of. This setup slows the blower down while running in the cool mode which causes the evaporator coil to be extremely cold. With the blower running slower and the coil being colder it allows more moisture to be removed from the air. If a home has high humidity due to infiltration, this setup will not correct their problem.

Sequence of operation for Dehum:

When dehum alone is needed (and overcool is setup) the unit will deenergize the ACC+ terminal and run the unit in cool. If overcool has been maxed out or has been set to zero then the thermostat will deenergize the ACC+ terminal but not run. The thermostat will wait for a cooling demand and deliver a reduced amount of airflow.