Chittering sound from drivebelt area at < 1500 rpm

[prwood]

Found this PDF from an AC compressor company with steps on diagnosing AC compressor noise:

http://www.sanden.com/objects/Compressor_Noise.pdf

Same company also has a service manual for their compressors which includes some diagnostic info:

http://www.sanden.com/objects/Sanden%20 ... Manual.pdf

Both seem to confirm the advice from folks here on going down the path of checking other accessory belt components, and the belt itself. It also mentions checking the belt and pulleys for oil or other contaminants. When I take off the belt to check pulleys, I can also clean the belt and all the pulleys to make sure they don't have any oil on them. Purple Power followed by water mist followed by compressed air would be my plan, but if there's a preferred method let me know. Assuming I would need to cover the alternator except for pulley when doing this.

[prwood]

Now that I have my car back I was able to continue with this diagnosis.

I did the water squirt test on the pulleys to rule out belt problems. No difference when water squirted on the pulleys while running.

Next I pulled off the belt. I turned the power steering, alternator, AC compressor, and tensioner pulleys by hand. All of them spun freely except for the power steering pump, which only spun for a little bit, which makes sense since it's part of the pump and the pulley actually needs power to be able to turn against the pressure of the power steering fluid. I also checked for play in the pulleys, and there was a bit on the tensioner pulley, but from what I've read that may be normal.

Next I cleaned the belt and pulleys, reinstalled the belt, and started the engine. The chittering sound was still present, so I moved around to try and isolate where the noise was coming from, and I'm fairly certain it is coming from the tensioner pulley.

The tensioner pulley is only $15 at AutoZone and seems fairly easy to swap out, so I may just go ahead and get that and give it a try.

[June]

I have had a ac clutch bearing go bad before and the noise goes away when the clutch engages. I noticed when more stress is on the belt from the compressor engaging causing the tentioner to pull in the noise sounds worse in your video. Notice the moment of the tentioner in conjunction with sound intensity caused by the extra resistance to the belt when the compressor engages.

You did not say you ran the engine momentarily without the serpentine belt to completely rule out something in the timing belt area causing the noise. After all you were just there last month but suppose you were sold a faulty tentioner or wheel and just happened to start making noise having nothing to do with your recent work on the alternator.

On my 1986 Buick Park Avenue the tentioner itself not the wheel started squeaking and had to be replaced. To my memory the tentioner bounced up and down during idle quite visible to the eye while looking at it causing a erratic squeak. Buick warranty replaced the whole thing and fixed the problem. I am not saying it is your problem but I thought I would mention the experience as the squeak sounds similar to my memory and went away above idle and was not a bearing on the wheel on the tentioner.

June

[abscate]

You should be able to isolate tensioner from AC clutch with garden hose

Tensioner is great news!!

[prwood]

Alright. Replaced the pulley and no change in the sound. Used the garden hose method and held it near each pulley and also near the timing belt and other areas of the engine for good measure. The sound is definitely coming from the tensioner, but more specifically from behind the pulley. Headed over to the store shortly to get the full tensioner unit.

[prwood]

Replaced the full tensioner unit and the chittering sound is gone. Everything on the belt drive is working properly and sounds at least as good as it did when we bought the car, maybe better.

https://photos.smugmug.com/Cars/2001-Vo ... 47-640.mp4

[jbeebo]

Brilliant! Nice work, it does sound good. This car's gonna be a real keeper at the rate you're going.

[jonesg]

Nice , when mine failed it melted the acc belt around the crank pulley and left black melted goo on every pulley, real mess to remove.