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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8511
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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J. Caldwell. I have my own HVAC business. I replaced a

Customer Question

My name is***** I have my own HVAC business. I replaced a defrost board on a Nutone 4 ton heatpump because there was power coming into the board and nothing coming out of the board to tell the contactor to engage. The system worked great for two weeks heat and cool modes, and now it is out again. Same issue. Power in 29v, no power out to contactor.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: Yes., thermostat settings fine, filters clean.
JA: Do you plan on doing the work yourself?
Customer: Yes, I am an HVAC technician
JA: Anything else we should know to help you best?
Customer: My trouble shooting procedure was this: Checked interior unit control board and fuse, checked good. Checked transformer, checked good, output is 29 volts. Contactor coil ohms read 16.8 and is functional. Power is coming to the defrost board from the thermostat at 29v, no power coming out of the board to the contactor
Submitted: 7 months ago.
Category: HVAC
Expert:  Phil replied 7 months ago.

Hello, if you can take a close up photo of the units wiring diagram for me and post it here I will mark it up with trouble shooting instructions.

Photo must be well lit and exceedingly well focused, use the attach files link next to the send button to get the picture to me.

I also need the model number of the nutone heat pump.

We can go from there

Customer: replied 7 months ago.
Model# ***** (4.0 Ton)
Customer: replied 7 months ago.
Your assistance is greatly appreciated.
Expert:  Phil replied 7 months ago.

Hello again, if the ODT (out door thermostat) is open then there will be no power to the compressor contactor. Locate that and tell me where its set and how cold it is outside, we can go from there

Customer: replied 7 months ago.
Found a filty dirty coil and a bad high pressure switch. Thanks for your help.
Expert:  Phil replied 7 months ago.

Good work!

It is time for you to rate my efforts, I will appreciate it. Thanks.