Servicing Carrier VRF Part 3

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