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HVAC School - For Techs, By Techs

May 13, 2021

In this podcast episode, Bryan and Eric Mele discuss the diagnosis and prevention of compressor overheating in HVAC and refrigeration.

The main causes of compressor overheating are inadequate cooling back to the compressor, low charge, restrictions, and sometimes even poor suction line insulation. We want to keep the suction temperature low while maintaining appropriate superheat. If the suction line temperature is too high, the compressor can't cool down well enough. Dirty condenser coils, low voltage, weak capacitors, or an inadequate condenser fan can also lead to compressor overheating.

Electrical problems, including too little capacitance, will make a compressor go out on thermal overload. When you have refrigerant problems, the thermal mass will just keep growing; it takes a long time to heat the compressor up, and it will take a long time to cool it down.

In a thermal overload, a bimetallic disk in the compressor will open and break all three legs of power. When a compressor goes out on thermal overload, it will make an open circuit, and you will read infinite ohms. Knowing that the compressor has gone out on thermal overload is just the beginning of compressor overheating diagnosis.

So, to begin diagnosis, you'll want to make sure there's refrigerant in the system. Inspect the unit visually and note anything that seems odd. Then, you'd check your capacitor for electrical problems. You can also feel the compressor to get an idea of the extent of the overheating (try not to burn yourself). You'll also want to monitor the amp draw, condensing temperature, suction pressure, and superheat.

Eric and Bryan also discuss:

  • Axial fans
  • Condenser fan intermittent failures
  • Resetting the compressor
  • Cooling down the compressor
  • Setting up your meter
  • Being out on high pressure
  • Wrapping wire to increase ammeter resolution
  • High return gas temperature

Learn more about Refrigeration Technologies HERE.

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