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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 953
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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The a/c turns off but the compressor motor keeps running. I

Customer Question

the a/c turns off but the compressor motor keeps running. I recently changed the compressor fan motor and capacitor. then the light on the control board kept flashing, so I changed the control board. the light is still flashing. a/c works
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: about two weeks.
JA: Do you plan on doing the work yourself?
Customer: yes. I can't find the next problem.
JA: Anything else we should know to help you best?
Customer: just need to know why the compressor would continue to run after the ac shuts down
Submitted: 2 months ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 months ago.

Hi I'm Brian and I'll be happy to help you try to diagnose this!

There are a couple things that can do that. Which one depends on the model of your ac unit. It could be either a compressor contactor with stuck or welded contact points. Or, in the case of some of the newer ultra-high efficiency units, the unit control board actually turns the compressor on and off and the board has a failure condition. I would need the make and model number of the unit to tell which it could be. If you want to send that info, I'll try to narrow this problem down for you.

Thanks,

Brian

Customer: replied 2 months ago.
trane xr80.
Expert:  Brian HVAC Guy replied 2 months ago.

Ok thanks. That unit will not have a control board that makes and breaks power to the compressor, the compressor will be started and stopped by a compressor contactor. So, either you have a stuck contactor or (and I forgot to mention this possibility earlier), you have a short in the low voltage control circuit somewhere between your thermostat and indoor unit somewhere that is causing a signal to run to be sent to your compressor when it shouldn't be. There are rare circumstances where a thermostat cooling relay is stuck but that is a stretch, disconnecting the wire at Y on the thermostat can confirm that.