* Cycling of the compressor clutch: The compressor itself doesn't immediately shut off when you turn the ignition off. There's a clutch that engages and disengages the compressor from the engine's pulley. It might be cycling a few times to equalize pressure in the system before fully disengaging. This is normal behavior and usually stops within a minute or two.
* Low refrigerant: If the system is low on refrigerant, the compressor might cycle longer trying to build pressure. This is not normal and indicates a leak in the system. It may also be accompanied by weak or ineffective cooling.
* Faulty compressor clutch relay or cycling switch: These components control the engagement and disengagement of the compressor. A malfunctioning relay or switch can cause the compressor to stay on longer than it should or even to run continuously.
* Faulty pressure switch: This switch monitors the pressure in the AC system and signals the compressor to turn off when the pressure reaches a certain level. A faulty pressure switch may fail to signal the compressor to turn off.
* Electrical problem: A short circuit or other electrical malfunction could be preventing the compressor from receiving the signal to turn off.
What to do:
1. Listen to how long it runs: If it runs for only a minute or two, it's *probably* normal cycling. If it runs for significantly longer, or continues to run intermittently even after the car has sat for a while, then there's likely a problem.
2. Check your AC performance: Is your AC cooling effectively? If it's weak or not cooling at all, a refrigerant leak is a strong possibility.
3. Have a mechanic diagnose the issue: A professional mechanic can diagnose the problem accurately. They have the tools to check refrigerant levels, test the pressure switch, and inspect the compressor clutch and its electrical components. Trying to fix this yourself without the proper knowledge and tools could be dangerous (refrigerant is harmful) and could lead to more expensive repairs.
Don't ignore this problem, as a continuously running compressor could damage the system or cause other problems. Get it checked out soon.
