How to Diagnose Faults in an Air Conditioning Compressor

In this article, we’ll explain how to determine if your air conditioning compressor is malfunctioning. We’ll cover the most common diagnostic procedures to quickly identify potential issues:

1. Open or Shorted Motor Windings
2. Grounded Compressor
3. Faulty Inverter Compressor Windings
4. Lack of Power to the Compressor
5. Mechanical Compressor Failure

1. Open or Shorted Motor Windings

To check for open or shorted windings:

• Set your multimeter to the ohms scale.
• Place one probe on a compressor pin and the other probe on a different pin. Repeat this for all pairs of pins.
  • Open windings: If any reading is 0 or infinite, the winding is open, and the compressor is defective.
  • Shorted windings: If any reading is close to 0 ohms, there is a short circuit in the winding.

2. Grounded Compressor

To test if the compressor is grounded:

• Sand a small area on the compressor casing to ensure good contact.
• Place one multimeter probe on the casing and measure with the other probe on each compressor pin.
  • If any measurement shows a value other than zero, the compressor is grounded and requires replacement.

3. Faulty Inverter Compressor Windings

In inverter compressors, resistance measurements between the pins should be very similar.

• If the resistances are inconsistent, the compressor may be damaged, even if there are no open, shorted, or grounded windings.

4. Lack of Power to the Compressor

Check whether the compressor is receiving power:

For conventional air conditioning systems:

• Inspect the relay on the electronic board and the thermal/overcurrent protector.
• With the unit powered off, test the protector pins for continuity (low resistance value).

For inverter air conditioning systems:

• Diagnose the IPM (Intelligent Power Module) using a multimeter on the diode scale:
  • Place the red probe on the negative terminal and the black probe on U, V, and W terminals. The readings should be consistent.
  • Reverse the probes and repeat the procedure. Deviations indicate a problem with the module.

5. Mechanical Compressor Failure

Even if electrical tests are correct, the compressor may fail mechanically.

• Symptoms include starting but not compressing or shutting off quickly due to shaft obstructions, which can cause overcurrent.