I'm trying to diagnose the squeal noise I'm hearing. Squeals at all RPM, even at idle. When the AC is turned on the sound gets a lot louder so I think it is the AC compressor. However the AC still works well. How can I tell if it's the compressor clutch or the whole ac compressor?

Or is it possible that it has nothing to do with the AC compressor and it's the belt or tensioner or pullies? I did a quick inspection of the belt and it looked fine, but it definitely could use a closer look.

It's a 2004 5speed

 

Check and see if its not an idler or tensioner first, this would be my first guess. When the ac is activated, it puts more strain on the idlers and could cause them to make more noise when the bearings are getting worn in them.

 

Okay, what's the best method for testing them? Thanks

 

lol, that's a good question! As the car's running check under the hood and listen. Next check if any of the idlers have excess play. then go from there.

 

One bearing should be louder than others, causing squeal.