Turnin on a/c results in engine bog down and then a/c turns off engine idles great,then a/c kicks back on,engine bogs down,this a constant cycle. A/C compressor is turns freely by hand,as i have done a/c for a number of years now ,I have gages,freon is not low or overcharged,jumpin low pressure switch makes no diff,discovered high pressure switch on side of compressor,but it has three wires in connector,not yet sure how to jump this one still researchin,I'm guessin engine computer is sensing possible belt failure and kickin out compressor.Any ideas anyone?This is on 04 trailblazer 4.2

 

Have you recently put in a new battery?
When I put a new battery in my 02 Trailblazer I had the same prob.
When I hooked up the new battery the A/C compressor was hit with a surge and blew. With engine on and car in park the rpm's would go waaay down, the compressor would turn off and the rpm's would come right back up. I had to replace the compressor. Now, whenever I disconnect the battery I also pull out the A/C relay.

 

No ,I did not have new batt. installed,thanks though for the idea,also i believe u have the cycle confused,when the compressor kicks on,engine bogs down then engine management computer,senses possible compressor failure or lockup and then releases compressor clutch and then engine revs up cause of lack of load,I have recently discovered the real cause of the problem,the throttle body needs cleanin on the inside of the housing around and behind the throttle blades,this totally resolved the prob on this vehicle,why ur comp blew,because of new batt,doesnt make sense to me,as numerous times in my many repairs of cars i have never experienced this result,I would think that the clutch simply gave out,or perhaps ur compressor maybe experiencing problems,as u say u replaced it.I googled the idle problem and the fix i performed came from this forum,thanks for all ur input,as sometimes i get stumped and i hope ur probs are solved.