1. Cabin temperatures higher than normal. One of the first signs that a compressor may be having trouble is the AC no longer blowing as cold as it once did. A damaged or failing compressor will not be able to properly regulate the refrigerant flow in the AC system, and as a result, the AC will not function properly.
How do you check a car AC compressor?
Turn on the AC. Connect a pressure gauge to the low side of the AC compressor, typically found on the firewall passenger side in the engine compartment. Add approximately 2 oz. of Freon to determine whether the compressor kicks on (if it does, you will hear a loud click followed by a puttering sound).