Thanks in advance for the help. It is appreciated.

I have an 01 Jimmy and the a/c compressor squeals a noise that can be heard throughout the vehicle when the compressor initially engages, but for only a 1/4 of a second, and only on rpm above 1500 or so. A small plume of smoke also escapes the area but I cant determine exactly where in the area it is originating, pesky radiator fan. A/c still cooling, cant tell if the squeal is in turn affecting the load on the motor. Any ideas? A/c was occasionally ran for a few minutes during winter to keep things juicy, this just started yesterday.

 

Was looking at it again. Tell me if this makes sense. The squeal and smoke is not made at idle, only when rpm is high. Does it seem like it might be the belt not grabbing the pulley at engagement? I know nothing about this. Just thinking if it were the compressor or clutch it would occur at any and all rpm ranges, but it does not. Faster rpm, more violent the squeal.

 

Does the compressor/clutch get hot after running several minutes? You may have a stretched belt, a malfunctioning spring-loaded tensioner or the compressor is getting ready to fail. I would remove the belt, engine not running, and hand turn all the pulleys turned by the belt to see if any are tight. Also, while the belt is off, turn on the ignition and A/C, make sure the clutch clicks closed, don't start the engine, then hand turn the A/C pulley. There should be some resistance but it should not be tight.

Edit: Added: If you suspect the belt is slipping and causing smoke, it is time to replace the belt anyway.

 

It sounds to me like it is probably the belt slipping on the A/C pulley. But I think you should follow Pewter2002 suggestions.
I would like to add, that precision bearings (by design) have a certain amount of resistance, that you will feel, when turning by hand. What you "don't" want to feel, is "side-to-side" looseness, or roughness. they should turn smooooth. my 2 cents.

 

Plain and simple, if its the belt or the tensioner, it will slip and make noise with the compressor on or with it off. If its only making noise with the ac on then I would have to say your compressor clutch is toast or the compressor is binding and about to be toast. Also check your idler pulley , it may be freezing up. Good Luck

 

Ok guys, thanks. I will replace the belt since I simply dont know when its last replacement was, no reason to risk a problem over a $40 part. I will also turn the pulleys while the belt is off. Spent some more time on it after last post and can definitely smell burning rubber during that 1/4 second squeal and puff of smoke. I will post back after belt replacement. I fear problem will persist through past luck. Is it logical that the compressor or clutch would be binding for only a 1/4 second and only at higher rpms?

 

Not necessarily binding during the first few seconds, but a load being added to an already suspected loose or worn belt could cause what you describe. Anything is possible tho. Trying the hand turn method will rule in/out an initially binding compressor. Remember, if you disconnect the A/C lines and remove the compressor, the system will need to be vacuumed out, oil (possibly) and coolant added when reinstalled.

 

Just found something out. I tried turning the front of the compressor with engine off but still attached to the belt, just messin around. Anyway, the (am assuming clutch) front part turns and of course nothing else does because it is still connected to the motor. While doing this, am I turning the compressor as well or just the clutch? Because I can feel a binding while hand turning if I apply pressure and turn, infact only as I start to turn it, does not continue after the metal type resistance I am feeling. Also, there is a reddish powder lightly coated on the front of the clutch.

 

Belt was perfectly fine, convinced it was the clutch. Sprayed TINIEST amount of Deep Creep into clutch and no more noise. False sense of security, maybe. But much cheaper attempt than any other i have found.

 

As you know, a properly functioning A/C compressor clicks when it activates. That is the electromechanical clutch pulling the front plate to the pulley face. Yes, when you rotate a part of the front plate assembly of the compressor, you are turning the compressor. If you push the plate towards the pulley area, there will be additional resistance. The dust you mentioned is probably from the clutch, meaning probable pending compressure failure. Of course, a small amount will be rust that accumulates if you seldom use the compressor. Spraying lubricant on the clutch reduces the initial pressure load by allowing it to slip more than designed, thus less friction and smoke. Final thoughts: you can replace the clutch pack on the compressor, but that won't be useful if you have a compressor is going south.