One of the leading causes of a car stalling with the A/C on is a seized compressor. If there’s screeching, smoking, stalling and the air blows warm out of the vents whenever the AC is turned on it’s a good guess that the compressor has locked up. If there is just a belt squealing but the car doesn’t stall and the AC cools, more than likely the belt or the tensioner is worn. The most likely cause of a car not idling high enough and sometimes stalling with the A/C turned on without any of the other issues mentioned can be an IAC (Idle Air Control) motor.
*Keep in mind the compressor could be hot to the touch when checking.
How to check for a locked up or seized compressor
If the belt is loose it may be because of a worn serpentine belt tensioner, but this alone won’t cause the car to stall. A sticking IAC motor can cause the car to stall. An IAC motor typically gets carbon build up that can cause sticking. If the idle doesn’t go up when the AC is turned on the engine can stall. Many times if this is the problem, the IAC motor can be removed from the throttle body and cleaned with a brush and fuel injector spray and then re-installed.