How to Test an HVAC Compressor

The compressor acts as the main cooling element for your HVAC unit. The compressor is responsible for raising temperature, density and refrigerant contained in your HVAC unit. The compressed vapor from the coolant is chilled by surrounding air in the HVAC unit creating cool vapor, which is spread throughout the system. A malfunctioning compressor will cause your unit to fail. Testing of the compressor unit may be necessary to determine whether it is the cause for an HVAC unit failure.

The compressor is a very important components of your HVAC unit.
  1. Remove all the wiring from the compressor terminals using a screwdriver to loosen the wiring. Clean the terminal with a dry, clean towel.

  2. Check terminals C, R and S on your compressor unit using your multimeter, which should be set to Ohms. Touch the meter between two of the terminals to test the continuity. Each terminal should have 30 Ohms resistance between C and R, R and S, and R and C. A high resistance and a cool motor means the compressor is bad.

  3. Test the capacitors of the unit. Set your multimeter to the capacitance setting. Turn off the power supply of the unit. Short the two terminals on the capacitors by holding a metal screwdriver between them to remove any potential for shock. Remove the wires from the capacitor. Place the meter leads on the capacitors for a reading. Good capacitors will read around 6 percent of the rating printed on the capacitor. Higher than 6 percent means the capacitor is bad.

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