Picture of Austin Caldwell

Austin Caldwell

Technical Services Manager
North Georgia District

I Need My Building Back Running Right NOW!

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:

  1. Go into the comfort link panel under “Temperature”.
  2. 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.
  3. 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.

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. 

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