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.
Loud noises when the compressor is running : Loud noises when the AC is switched on is another potential symptom of a failing AC compressor. Much like other accessories driven by the engine's belts, the AC compressor has several interior components and uses a sealed bearing to turn.
Compressor clutch is not moving : Another sign of a problematic compressor is the clutch not moving. The clutch on the compressor is what allows the pulley to engage and disengage from engine power so that the compressor is only turning when it needs to be.