00' Sonoma rattling at idle with the ac on

Maintenance/Repairs
1

I recently bought a 2000 Gmc Sonoma SLS and it’s been a headache ever since.
Ever since I got it, it’s made this rattling sound that only occurs when I’m both idling and when the AC compressor is on.
The sound is intermittent and sounds like something rattling against a large metal pan. Whenever I turn the AC off or pick up the RPMs, it stops like it was never there.
My first thought was: belt tensioner.
So I popped the hood and watched the tensioner at idle and it seems to be moving back & forth a lot more than I think it should, however, there’s not much give at all when I push on the belt itself.
Any ideas?

2

This could be an indicator of impending compressor clutch failure.

3

Try spraying WD40 with the straw into the guts of the tensioner if you can find a gap. I’ve had this quiet a tensioner temporarily (and tell me I needed a new one). Can you get a screwdriver on the compressor and up to your ear? That might pin the source down. (Keep the screwdriver away from the belts!)

4

From the description ( The sound is intermittent and sounds like something rattling against a large metal pan.) I think it is an exhaust heat shield

5

The belt tensioner shouldn’t move at all. If it does it means the spring in the tensioner has become weak.

Replace the tensioner.

Tester

6

I replaced the tensioner today and however it did reduce the slight wobble, it didn’t solve my problem. So I took it back so I could use that money for something else.
So I guess that rules out a bad tensioner
I did the screwdriver thing on the ac compressor and heard the most god aweful racket I’ve ever heard.
I’m assuming that’s the source of my issue.

Now, the question is, is it as simple as a new clutch or am I going to have to replace the entire thing?

7

Here’s a video I took today of the noise

8

I was unable to access the video, but the description sure sounds like a clutch bearing failing. The wobbling of the tensioner sounds like a manifestation of a clutch pulley no longer spinning coaxially to the compressor operating axis. I’ll bet if you removed the belt you’d be able to manually wobble the pulley.

9

When I replaced the tensioner, I checked all of the pulleys for any play or wiggle room and they all seemed solid, including the ac compressor.

10

I’ll still stick with my guess, even though it seems solid when not under load.

11

I’m going to say you probably have a failing AC clutch as well. When it will fail could be days, weeks, months or years. BTW…one problem and this 15 year old vehicle is a headache? You should always get a used vehicle checked by a good independent mechanic before you buy since it will usually keep these “headaches” to a minimum.

12

“one problem and this 15 year old vehicle is a headache?”

;-))

If that compressor clutch has lasted for 14 years, that actually isn’t a very bad record.
On my brother’s '70 Barracuda, the compressor clutch “grenaded” in less than 2 years.

As I mentioned in a different thread on the newer Dodge Challengers, for those who are filled with nostalgia for the old Challengers, you have to be aware that they (and their Barracuda twins) were just not well-built cars.

13

It was a gift.
First car.

14

Gotta go with the compressor internals going bye-bye. When the AC is ON, the clutch is locked up and shouldn’t make that noise.

15

Get a new compressor installed now. It’s a very routine repair. Just about any shop with an ac service machine will be able to do this

Also replace the accumulator and the orifice tube. May as well throw a new belt on, while you’re at it

If you wait, it’ll let go catastrophically and contaminate the entire AC system with debris. And then it’ll get much more expensive to fix