I have being looking at this post for a couple of days now but don't quite know how to answer it without being a little sarcastic cuz I know that you know how to turn the a/c on, that usually turns the compressor on but I think your question has to be other than that. maybe how to activate the a/c compressor cuz is not coming on. anyway we will all like to help you if we only knew what your trying to do. hope to hear from you soon.

 there is a a/c relay control... gm--powertrain--active test--engine--a/c relay.  this will enable/disable the a/c relay to check half of the circuit involved.

 

 

bill