i just bought this used car (YESTERDAY!) from the dealer... 51k miles on it... 2007 base model. I didn't get to drive it till tonight and i noticed a scratchy metal grinding noise from the front of the car. Sounded like the noise was coming from the front of the engine. Weird thing is the noise goes away when i turn ON the AC... and comes back when i turn it off...

ANYONE ENCOUNTER THIS BEFORE?! i'm freaking out cause i just bought it!! i'm planning on taking it to the place i bought it and hoping the 60k warranty will cover whatever the problem is...

any ideas?!

 

That's the AC compressor clutch. There's a ball bearing between the pulley and the compressor to allow the pulley to turn when the compressor isn't running. The clutch is electro-magnetic.

The fix is going to be expensive, as they'll probably want to just replace the whole compressor assembly. The AC system will have to be bled before the compressor is removed, and recharged after it's reinstalled.

The bearing is usually replaced when the compressor assembly is overhauled.

The compressor normally cycles on and off when the AC or defroster is on. If the noise is gone continuously when you switch the AC on, the compressor is probably bad.

For about ten years, I designed and built special-purpose winches than used clutches I had scavenged off old AC compressors. I've only seen one bad bearing out of dozens of clutches.

 

AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!! how much is expensive?! is this covered under the factory warranty???

 

I doubt it's going to be covered by the factory warranty, since it's not part of the drive train. I'd guess several hundred for the rebuilt compressor and at least that much for labor, depending on where you have the work done.

 

I hope this doesn't turn out to be a nightmare; but, Dude!
How did you buy a reasonably expensive used vehicle without driving it!??!!! What was the thought process there? You said you got it from a dealer, too but I hope you got it for auction price if you didn't even drive it first.

 

Keep in mind that what you just read is a shot in the dark diagnosis as none of us have seen or heard your car. Don't jump out the 10th story window just yet. In my experience, AC clutch failure is indicated when you turn the AC ON, not when it is not running. Keep in mind that when you turn the AC on, the idle speed increases. What you hear might be related to the idle speed and nothing at all to do with the AC. Just sayin.....

 

i did test drive the car...twice! two different times... never heard the noise before until last night!

about to call the dealer.... FML

 

Oh. I guess I misunderestimated the part where you said:
Anyway, I hope it works out.

 

The clutch itself can keep working even if the bearing is bad.

One other possibility I just thought of is a broken spring on the compressor clutch disc. That would let the disc drag on the pulley causing the noise. The noise would go away when the AC was turned on, since the disc would be held tightly against the pulley.

You might be able to check that yourself if you can see the springs on the disc. It probably looks something like the picture here:

http://cgi.ebay.com/ebaymotors/03-04...Q5fAccessories

The three straps are the springs. I couldn't find a picture for the compressor on an '07 model, so it might be different.

 

some update..

just got back from the dealer... grueling 4 hour wait. it's like waiting for your loved one in surgery or something. ANYHOW. they checked it out and as we all knew the noise was coming from the AC compressor. They said they lubed and cleaned the clutch with brake cleaner and the sound went away. They let the car sit and tested it again after it got cold and still no sound (for now, knock on wood). This seems like a temporary fix to me... hopefully it doesn't come back...

 

You were lucky. I don't know where you are, but maybe the previous owner hadn't used the AC much for a while, and the clutch surfaces got rusty. There's nothing else to lube. The surfaces are normally self-cleaning, since most people run the AC or the defroster often enough to keep them clean.



The clearance between the disc and the pulley is only several thousandths of an inch when the clutch is disengaged, so not much can get in the gap. The bearing is sealed and pretty much inaccessible, so there's no way to lube it.

Hope it continues to work well.

 

Noise is back............

 

Bummer. That didn't take long.