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The Art of Troubleshooting Compressors

Updated: Jun 20


Technicians must act quickly to figure out why a compressor is struggling to perform


The compressor is the heart of any air conditioning or refrigeration system, so when it starts showing signs of not working correctly, technicians must act quickly in order to find out what is wrong. But identifying the reason behind why a compressor is not performing optimally can be a challenge, because there are a variety of reasons why a problem may occur, and by the time the problem is discovered, it may be too late for the compressor.

For systems showing signs of compressor trouble, technicians should employ comprehensive troubleshooting techniques in order to isolate the problem.

Signs of Distress

Systems showing signs of a compressor problem may exhibit a variety of symptoms, said Jamie Kitchen, account manager at Danfoss, including:

  • Compressor not starting when the start contacts close;

  • Excessively low/high evaporator pressures (compressor/condensing unit over or undersized for evaporator/metering device;

  • Loud noises generated by compressor; and/or

  • Lack of pressure differential between the suction and discharge pressures.

If any of these symptoms occur, then Kitchen recommends performing the following troubleshooting steps:

  1. On both single- and three-phase compressors, verify if start contacts are closed. Check voltage at compressor to ensure it is within the correct range and ensure wires are connected properly at compressor. On single-phase compressors, make sure the start capacitor and relay are functioning as required, and if there is an internal overload, test it to ensure it is closed.

  2. Check the compressor model against the unit nameplate and evaporator to make sure it is correct. Also verify the compressor voltage rating is the same as the supply voltage.

  3. Three-phase scrolls will reverse-rotate if the incorrect phase sequence is connected to it. If scroll is running backwards, it will be very loud and will not build pressure.

  4. Check reciprocating compressor valves by pumping down system and determining if refrigerant is leaking past the valves. If it does, valves are not sealing properly.

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