One of the main causes of a car stalling with the A / C on is a seized compressor. If there is screeching, smoke, stagnation, and hot air comes out of the vents every time the air conditioner is turned on, it is a good assumption that the compressor has locked out. If there is only one belt squeaking but the car won’t stop and the air conditioner cools down, the belt or tensioner is most likely worn out. The most likely cause of a car not idling high enough and sometimes stalling with the A / C on without any of the other issues mentioned may be an IAC (Idle Air Control) engine.
* Please note that the compressor may be hot to the touch when you check it.
How to check for a blocked or stuck compressor
- Try rotating the clutch plate (at the compressor end).
- Using a bushing on the nut that holds the clutch plate, see if it can be turned.
- Look for signs of overheating of the clutch disc; discoloration.
If the belt is loose, it may be due to a worn serpentine belt tensioner, but this alone will not cause the car to stop. A stuck IAC motor can cause the car to stall. Typically, an IAC engine generates carbon build-up that can cause it to stall. If the idle speed does not increase when the air conditioning is turned on, the engine may stall. Many times if this is the problem, the IAC engine can be removed from the throttle body and cleaned with a brush and spray fuel injector and then reinstalled.