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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8695
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a trane combi temp/humidity sensor BAYSENS036A. Can I

Customer Question

Hi I have a trane combi temp/humidity sensor BAYSENS036A. Can I wire just the thermistor or does it require loop power to the humidity sensor.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: just today. the electrical contractor wired the thermistor to the humidity connection on the control board which has 24 vdc and the thermistor now reads 5.7 degrees F even though it is at room temp.
JA: Do you plan on doing the work yourself?
Customer: I've connected the thermistor back to the correct terminals in the control panel but it still reads 5.7 degrees F and I'm not sure if the thermistor is faulty or if the temp/humidity unit needs both sensors to be wired in order to work properly
JA: Did you double-check the thermostat? And what about the unit's filters?
Customer: I didn't check the resistance value of the thermistor. What filters?This is a room sensor.
JA: Anything else we should know to help you best?
Customer: No I just need to know if this looks like the thermistor has been damaged by overvoltage or if the unit requires both the humidity and temperature sensors to be wired in order to work properly?
Submitted: 10 months ago.
Category: HVAC
Expert:  Phil replied 10 months ago.

Hello. If this is what you have, such a wiring error would have damaged the printed circuit card (control board) that the sensor connects to most likely.

If that is what you have you can wire wire them separately, the thermistor is a resistance circuit only, if that fails you will need to replace the entire humidity/ temperature sensor and quite possibly the control board.

We can go from there as needed, if you want to do some tests you will need both a vdc and 4 to 20 miliamp signal generator.

Note regarding electricians: One in a few hundred is a qualified HVAC controls man, the rest are only trained in running the power connections to equipment, no controls and nothing internal to the units... that is an HVAC specialty.

Customer: replied 10 months ago.
Thanks for your reply.
This is what I suspected as well.
I need to check the input on the controller as well just to make sure the channel is ok.
They mistakenly connected the thermistor to the humidity temp sensor input and left it there for over two weeks so I think that has done the damage.
I need to check the controller temp input channel but it wasn't connnected so it should be fine and I have a 10k ohm resistor which will work fine for testing.
We have a trane contact that I can call for a replacement unit, I think it's a pretty common part, so that should fix the problem.
Just wanted an expert opinion before I proceed.
Thanks for your help.
Expert:  Phil replied 10 months ago.

You are welcome.

It is time to rate my input now, I will appreciate it, simply select one of the stars... my favorite one is 5 stars of course.