WHY DOES MY 2003 TRAILBLAZER cut off when i turn on the Air Conditioner?

Question

this only happens when I am idle

Answer 1

overcharged air conditioner or a/c compressor binding also.  IAC valve may be compensating but can't compensate that much.  What happens when you turn on the A/C while driving and then come to a stop?  Does it still kill it?  You probably have a tachometer in that vehicle so watch it while giving just enough gas to idle it around 750 or so and see how high the RPM needs to be before the engine won't die when turning on the A/C.  If its just the IAC, you shouldn't have any problem with it dying by turning on the A/C at 750.  

Answer 2

Idle air control valve is not compensating. Probably the sensor that controls that gave out.