2002 gmc envoy shuts off when i turn on the ac whil ideling

If it does it when idling I would suspect an IAC motor (Idle Air Control). If it is opening too slowly the added air the motor needs will not be supplied fast enough and the engine will kill.

It could be other things also but this is where I would start.

There is often an A/C idle up vacuum switching valve in the system, which is electrically operated. It causes vacuum to be applied to a diaphragm which opens a passage from the air cleaner to the manifold. These VS valves fail usually when they are hot. If you test it when cold it is OK !!

The trouble is this VSV can be mounted anywhere in the engine bay, but if you have a vacuum line diagram it will be shown there. A typical valve -

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/1c/cc/40/medium/0900c152801ccc40.gif


The other way of getting A/C idle up as Travis says is with a small stepper motor on an IAC valve, which controls idle. This valve tends to gunk up, and the motor is then unable to move it full range. A clean with carby cleaner spray will usually do the job.

I regret I don't know which system you have, or even both!
.

Take off your throttle body and clean it...I had the same problem and thought the same thing you are right now, but it works.

Your a/c needs maintenance the pulley bearings needs to be overhauled
Ac's power drain rest of the vehicle out puts cause its putting strain on alternator and battery
Have battery and alternator checked
Above 12 volts good below 12 volts bad use volt meter with dc current just connect to battery