Tensioner bouncing violently above idle

[Trebuchet06]

Thanks for reading everyone!

This is a 2002 Chevy Silverado 2500HD, we have owned it for a few years. I noticed a knocking noise when the AC was running, it was loud enough to hear while driving. I couldn't figure out what it was, and shortly after when the AC quit working, I noticed that the AC belt was broken. Replaced the belt, the noise came back while driving. Standing at the engine and revving it by hand you can make the tensioner jump pretty violently. It was jumping bad enough to break the previous belt. The AC still works, and blows cold air, but if you rev the engine much above idle, the belt will sometimes squeal, and the tensioner starts jumping back and forth. So, I replaced the tensioner with a new GM tensioner and the behavior continues.

I haven't been running the AC, and have taken the belt off just to not further damage anything. My guess is that the AC compressor is starting to lock up, or the clutch is engaging incorrectly? I'm not sure if the clutch even could do that.

I don't know the history of the AC system as I've only owned the truck for a couple years.

Thanks for any help you all might have!

[Cusser]

We had same symptoms on our 2005 GM Yukon Denali (6.0 engine), kept breaking the separate belt but AC would work fine otherwise, but make some noise at times. My investigations indicated faulty compressor due to "slugging", because the AC compressor is mounted so low on the engine.

To fix ours, I installed a brand new compressor (get from sponsor ACkits.com) and AC belt, added some PAG oil and new R134a with no conditioners and sealant, and problem was away. I did not flush anything or change the accumulator or orifice tube either because I figured the system would still deliver cold air until the belt would snap. With the brand new compressor I also installed an accessory module designed to prevent this called the Deslugger from Four Seasons, which simply plugs in. Unfortunately, one cannot fix such bad compressor after the fact by adding a Deslugger !

[Trebuchet06]

Thank you Cusser!

I'll check out the Deslugger and start planning on replacing the compressor.