NEED HELP 05 i6 AC compressor noise


Active Member
My girlfriends 05 trialblazer has 215k miles. The AC compressor has started making a knocking sound whenever it engages. From what I've read I believe it's the bearing.

We'd like to fix this as cheap as possible and avoid buying a $200 compressor.

I'm thinking of pulling a compressor off a junkyard trailblazer for $45 then swapping the clutch out. This would save a lot of money and prevent having to evacuate the AC system.

Does this sound like a good idea?

What speciality tools are needed and what exactly needs to be removed to do this job in the engine compartment?


If it's the clutch bearing, it would make noise when not engaged. If it makes noise only when it's engaged, the compressor itself is likely done. Check to see if the clutch is slipping which can be remedied by removing the shim under the clutch.
Air conditioner clutch shim removal

Another possibility is that it's overcharged.


What about when it's not on? Quiet? Would be worth to hear it engage and disengage to be sure. It did sound pretty bad. I thought it was the engine knocking.


Active Member
Yesterday I replaced the AC Clutch bearing just because it was easy to do and IMO worth trying before getting a new compressor.

Thing is, I had difficulty reinstalling the AC Clutch plate. When I pulled the pulley off, I must have mucked up the threads.

When I put the AC clutch plate back, the nut wouldn't fit on. So I cleaned the threads, and used a new 14mm nut instead of the 13mm (same threading size just different socket used). Thing is, when I tightened the nut, the clutch plate was stuck engaged. I ran the engine like that, cyclcing AC on and off and the knocking was gone but the clutch was staying fully engaged.

I loosened the nut and ran it again, and the plate was disengaging properly but the knock was back.

Could the clutch be slipping? It has two shims in there that I put back. Should I remove one? What is the proper way to tighten the nut on the plate so that it doesn't get stuck engaged but also isn't slipping?


Active Member
To anyone finding this thread later with a similar issue:

Compressor has been replaced and noise is gone.

When I took the trailblazer to get the freon evacuated, only about a pound came out. So I believe the old compressor was leaking. I replaced the drier, orifice tube, and compressor, and pumped out the moisture as well as did a leak test. The new system holds pressure fine so I'm hoping I fixed that. I added the proper amount of refrigerant (30oz for non-EXT) and air is ice cold now.

Probably should have just did this from the get-go, but it wasn't too much a waste of time replacing the pulley bearing. Plus I learned something new. Total including all parts, evacuation cost, refrigerant, renting tools (gauges and pump)= $318

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