I have a 2004 Gmc Envoy when I turn on the heater the compressor clutch stops then starts again, also at the same time the idle on the truck changes and tries to stall. It does heat also when I use the a/c it does the same. If I crank the heater to high the engine shuts off.
A/C problems on 2004 GMC Envoy
It sounds like an idle air control problem the engine's electronics controls the idle speed. If the power train computer senses electrical load, steering load or air conditioning load on the engine this effects the engine speed and the computer bumps up the engine idle speed. A failure in the idle speed control system or a vacuum leak can effect idle speed. Under certain conditions the powertrain computer shuts off the a/c.