Air conditioner troubleshoot: outdoor unit not running
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Power to the outdoor unit but unit not running
When voltage check at outdoor unit reveals high voltage power at the contactor but contactor is not closed, look for low voltage power to contactor coil.
With the voltmeter, check for power at the contactor.
With the voltmeter, check for power at the contactor.
The following videos explain the operation and troubleshoot of HVAC contactors.
The contactor is closed and power is available at the outlet of the contactor. Outdoor fan is running.
If the outdoor fan is running but the compressor is not there is power available at the outlet of the contactor. To determine if the compressor is running, check amp draw at the contactor. If the amp draw is too low (checkout the video below), there is an open circuit somewhere between the contactor and the inside of the compressor. This could be a burned wire at the contactor or the compressor, the motor inside the motor/compressor hermetic unit has an open winding or the compressor has overheated and the internal overload is off.
Sometimes the contacts of the contactor will overheat because they do not make good contact with each other. When they do, the contacts overheat (See "how to test for overheated HVAC equipment contacts"). The video below looks at a set of contacts that have overheated.