Common Signs of a Faulty AC Compressor and How to Address Them

Set the thermostat to a lower temperature than the room and see if the air coming from the vents is cool.
If the AC is blowing warm air.

Turn the AC on and listen for any strange noises coming from the outdoor unit
- Rattling or banging: This could indicate loose or broken components inside the compressor.
- Hissing or bubbling: May indicate refrigerant leaks.
- Buzzing or humming: A sign that the compressor is trying to start but failing.
- Clicking: Could suggest the compressor is struggling to turn on.

Refrigerant leaks can cause the compressor to malfunction or overheat.
Signs of refrigerant issues include:
- Ice buildup on the evaporator coil.
- Hissing sounds from the outdoor unit.
- Oily residue around the compressor.

If the compressor isn’t turning on, check for any tripped circuit breakers or blown fuses in the breaker panel.
Use a multimeter to test the capacitor (often located near the compressor). A bad capacitor can prevent the compressor from starting.

Turn off the power to the AC unit at the breaker.
Set the multimeter to the ohms setting.
Test for continuity across the compressor terminals (common, start, and run).
If you find an open circuit or extremely high resistance, the compressor is likely burned out.

A compressor that has shorted to the ground will trip breakers and prevent the system from working.
Use a multimeter to check for continuity between the compressor terminal and the metal casing.
- If there’s continuity, the compressor is grounded and will need to be replaced.

If the compressor is failing, it may cause the AC system to run inefficiently, leading to increased energy consumption.
Compare your energy bills from previous months to see if there’s a noticeable increase in usage.

A hard start happens when the compressor struggles to turn on and may take multiple tries. This could indicate wear or a bad capacitor.
If the compressor fails to start at all, it may be due to:
- Burned-out motor: The compressor motor may be damaged, requiring a replacement.
- Bad capacitor: This part is responsible for helping the compressor start.
- HP / LP Trips: If compressor Turns ON & OFF Continuously. HP / LP Switch might be defective.

Dirty or clogged condenser coils can cause the compressor to overheat and fail prematurely.
Make sure the condenser coils are clean and free of debris, which allows the compressor to work efficiently.

Compressors that are overheating will shut down to protect themselves. Check the unit for signs of excessive heat.
Overheating may be due to refrigerant issues, clogged condenser coils, or electrical faults.

Cooling issues and warm air could indicate compressor failure.
Listen for strange noises (buzzing, rattling, or hissing).
Inspect for refrigerant leaks or check electrical connections.
Use a multimeter to test for continuity and grounding issues.
Check the compressor fan, condenser coils, and capacitor.
If the problem persists, contact a professional HVAC technician for a full diagnostic.
Check for HP/LP Switch.

Following these steps can help you determine if your AC unit’s compressor is faulty and whether it needs repair or replacement.