Troubleshooting
AC Compressor Not Running: What to Check
6 min read••
The compressor is the heart of your AC. When it won't run, cooling stops. Here's what might be wrong.
The compressor is the most critical—and expensive—component in your air conditioning system. When it won't run, diagnosis is important.
Signs the Compressor Isn't Running
- Outdoor fan runs but you hear no compressor hum
- Indoor air is room temperature
- Energy bills drop but house doesn't cool
Check These First
Power to Outdoor Unit - Check the circuit breaker - Check the disconnect switch near the unit - Look for a blown fuse in the disconnect box
Thermostat Settings Ensure it's set to cool and below room temperature. Wait 5 minutes after changing settings before the compressor should start.
Capacitor The start/run capacitor gives the compressor the initial boost to start. A failed capacitor is a common cause of compressor issues.
Common Compressor Problems
Overheating Protection Compressors have thermal protection that shuts them off if overheated. Causes include: - Dirty condenser coils - Low refrigerant - Failed condenser fan - Electrical problems
Locked Rotor The compressor motor is stuck. Sometimes this is temporary (thermal protection), sometimes permanent (mechanical failure).
Electrical Failure Burned windings, failed connections, or grounded wiring can prevent operation.
Professional Diagnosis Required
Compressor issues require professional diagnosis because: - Refrigerant handling requires certification - Electrical testing needs proper equipment - Misdiagnosis can be costly
If your compressor isn't running, call for service rather than attempting DIY repairs.