Display shows “CMP” or compressor error; unit will not heat.

Safety first: High voltage and stored energy in capacitors can be dangerous. Turn off power and discharge capacitors before testing.

• Listen for operation: When commanded on, note whether you hear the contactor pull in and the compressor attempt to start.
• Check contactor: Inspect for burned or pitted contacts. Replace the contactor if damaged.
• Test capacitors: Use a capacitance meter to test compressor start/run capacitors. Replace any that are more than 10% out of rating.
• Compressor diagnosis: If capacitors and contactor are good but the compressor will not start or trips breakers, a technician should perform further tests. Compressor replacement is a major repair.