Rattle sound underhood with AC on?

joemomma · Jun 14, 2021

So just noticed today, the car has a rattle of some sort from under the hood with the AC running. Turn the AC off, and no rattle. I just noticed it at lunch when I stopped to get gas. Thoughts? Bad bearing on the compressor? Compressor loose? The PO said the compressor had been recently replaced, so that's my first stop. I'll check mounting bolts and look for anything out of whack.

Side note: AC works great, so I'd hate to delete it. But, I don't want it to be something that could end up chewing up the belt and leave me stranded. It's too hot for that nonsense.

joemomma · Jun 15, 2021

So it's definitely coming from the passenger side. It could possibly be the tensioner pulley - I noticed a lot of movement with it, but that may be normal. It also sounded like it was possibly coming from the passenger side towards the top - possibly a hi pressure line moving around somehow? I couldn't get in there and check things real good, it was stupid hot.

RAU03MACH · Jun 15, 2021

possible idler tensioner or the pulley on it
you did say a/c is working correctly
when the a/c is on dose the compressor cycle that could be the noise you hear

joemomma · Jun 16, 2021

The more I think about it, the more I think it's the tensioner. It was bouncing around like crazy, and the noise I hear is definitely metallic. Like a light "tap tap tap" more than a constant rattle. It will tap a 2-3 times, then quit.
Yes, AC does work and the compressor cycles on/off. It's not the compressor cycling, the noise is definitely coming from passenger/top side. It doesn't necessarily coincide with the compressor cycling either.

EDIT: for $100 or so, I can replace the tensioner and all the idlers. Might be $100 well-spent.

RAU03MACH · Jun 16, 2021

One thing to try remove belt
If you can pull up on tensioner by hand, I would say
weak tensioner and also try with a 3 8 wratchet
Just to see if it is your problem