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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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I am having a problem with my compressor. Thermostat

Customer Question

Hello, I am having a problem with my compressor. Thermostat is on and fine, air handler in the attic is moving air, but the compressor is not coming on when I call for cooling from the thermostat.
Submitted: 2 years ago.
Category: HVAC
Customer: replied 2 years ago.
I am getting 240 V to the unit, measured at the inlet wires to the contactor. I have replaced the contactor and capacitor both just as an attempt and also as standard maintenance, as we live at the beach and things like to corrode. We had a tech out last week and he had checked the coolant pressure at that time and said it was OK.
Customer: replied 2 years ago.
The compressor will run when I manually push the plunger on the contactor in, but will not engage at all on its own from the thermostat call for cooling.
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! It sounds like you are not getting 24 volt control voltage to your compressor contactor. This can be caused by several different things:1) You have a clogged drain switch at your air handler keeping the cooling off to prevent water damage. If this is the case you should clear and clean the clogged drain with a wet-dry vacuum.2) You have a high or low pressure switch tripped on your outdoor unit. This generally requires a manifold gauge set to check the refrigerant pressures to determine the cause.3) You have a failed time delay relay in your outdoor unit (if equipped) and it needs replaced. This requires either changing the part (if equipped) or using a volt meter to diagnose.4) Your compressor contactor coil has failed and the contactor will have to be replaced. This requires either changing the part or using a volt meter to diagnose. These are by far the most common causes of this symptom. There are some less common problems that can cause this as well. Please reply if you have further questions about this. Otherwise, if I have answered to your satisfaction, please remember to rate positively before you leave! Bonuses are welcome and very much appreciated! Thank you,Brian
Customer: replied 2 years ago.
Then how would I go about testing for each of these problems? I do have a multimeter.