check a/c compressor and belt.
The AC pump is bad. When the AC is turned on the pump tries to turn, because it is bad the extra strain on the motor causes it to stall. Be carely this can break or through a belt. In short its like putting a "brake" on your motor.
With the ac off your clutch the outer non belt driven part will not be turning. When it is turned on it will start to spin.
In some cars. one belt drives both the alternator and the air conditioning. In other cars, each has its own belt. Depends on the car. The alternator belt runs whenever the engine is running, the AC belt turns, but is only running under load when the AC compressor is turned on to get cold air.
Check for a slipping drive belt between encine crank pulley and AC compressor pulley.
Replace your a/c evaporator filter under dash. Liquid refrigerant is getting back to compressor causing belt to break.
Belt slipping? due to bad adjustment or glazing
power steering fan belt. It happened to my neon whenever the air was on. Try driving without the air on, if it runs fine then it is the fan belt. Mine squeeled when i turned on the ac and when i turned...$10 for a new AC belt and $40 service fee to have it installed. My car no longer sqeeks, and the AC is WONDERFUL!
Most likely the ac belt is loose and needs to be tightened or replaced.
You need to loosen the belt tensioner. There is a large bolt that needs to be loosened in the center of the tensioner pulley. Then the small vertical bolt is turned in the direction to loosen the belt. After the tensioner is loose replace the belt and retension it.
The compressor or it's pulley may be locked up or there may be something not aligned properly.
The ac belt has a tensioner that is accessed from below, and takes a tensioner tool to loosen. Remove the serpentine belt, release tension on the ac belt then the belt can come off for replacement.