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Regan Land
Regan Land, HVAC Technician
Category: HVAC
Satisfied Customers: 587
Experience:  18 years of experience, NATE Certified, Licensed HVAC Contractor, Certified IAQ Specialist
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outside unit of heat pump not working. just a hum from a

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outside unit of heat pump not working. just a hum from a switch.

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The switch with the hum is likely the contactor. It is possible that it either isn't making good contact or that there is no high voltage to the unit.


Let's start by checking the breakers to make sure they aren't tripped. Also, if there's a disconnect on the wall by the outside unit, make sure it is on.

Customer: replied 7 years ago.
I think it is the capacitor, what do you think?
It could be the capacitor... is it a dual capacitor (both compressor and fan connect to it)? Let's try to spin the fan motor with a screwdriver when you hear the humming sound. If it's a bad capacitor, the motor should start to turn. Also, if it's the capacitor, the fan motor and compressor will be hot to the touch.
Customer: replied 7 years ago.
yes the capacitor is dual. we had a power surg and then the unit didn't run. should I turn on the power at the breakers then try to spin the fan?
No, try to spin it while the thermostat is calling for cool and you hear the humming sound.
Customer: replied 7 years ago.
ok fan is running slow, but compressor not running
Definitely sounds like a capacitor then. Look on the side of the cap for the rating. There will be a microfarad rating (uF) and a voltage rating (370v or 440v are the most common). Check to see if the local air conditioning distributor will sell to the public. If not, a dealer will likely sell you the part (just make sure to write down where the wires go or replace wire for wire).
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