- How to diagnose a burned-out air conditioning compressor
- When is a compressor at or near end of its life?
- Air conditioner compressor defect diagnosis
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This chapter of "How to Inspect the Central Air Conditioning or Cooling System" discusses the
how to diagnose and replace a burned out air conditioner compressor, including
evaluation of air conditioner compressor noises, hard starting, lost cooling capacity, and detection of a burned out
compressor or A/C compressors at or near end of their life. Maintenance tips including attention to compressor support
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How to Diagnose a Burned-Out Air Conditioning Compressor
When a sealed compressor motor has "burned out" this means that the internal wiring of the motor has become
irreparably damaged: the compressor motor windings may be burned and shorted together or shorted to the steel shell
of the motor, or the windings may have burned and simply become "open" or disconnected. If the motor has burned
out in either of these ways it needs to be replaced.
When an air conditioning compressor has "burned out" by shorting of internal components - it will fail to start at all. This failure is detected
by disconnecting all power and wiring from the unit and measuring resistance (ohms) between the motor start/common and run/common terminals.
If there is zero resistance the winding is open or broken.
If you measure the resistance across a compressor winding and your meter's needle is stuck over at infinity,
or "OL"/"OVER" on a digital meter, that would indicate the compressor winding is open (burned through).
The same effect can be observed from simply connecting the meter to absolutely nothing.
If the resistance measured across the air conditioning compressor winding is too close to 0 ohms, it's shorted.
The compressor should blow the fuse or trip the circuit breaker when power is turned back on.
But watch out: we get field reports of equipment burn ups and even fires when the air conditioning circuit breaker for the
compressor happens to be an old FPE Stab-Lok or Zinsco unit.
If there is
resistance between the motor terminal and the motor casing, the motor has become shorted to ground internally and the unit needs to be replaced.
If there is no resistance between the start and run terminals to common, but there is resistance between the start and run terminals, this means
that the internal motor overload protection circuit is open. In this last case, allow the motor to cool and re-test it before replacing it.
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