Contour Enthusiasts Group Archives Forums General Troubleshooting Help diagnosing belt squeal: tensioner vs. AC comp.

Any suggestions for tracing down the source of a squealing accessory drive belt? I have read many posts on this topic about replacing one part after another until it goes away, but there must be a smarter (and cheaper) way.

I suspect the A/C compressor (or clutch) and/or the automatic tensioner. The squeal comes immediately on engine startup, worst when the engine is cold, but goes away after 10-30 seconds and never comes back while running. It happens even if the A/C is not turned on, but if you wait til it stops then turn the A?C on, it may squeal again when the clutch engages.

The sound is most likely coming from the A/C pulley, but the clutch is engaging and the pulley is spinning and the A/C is still blowing cold. Drive belt is 1 yr/10k mi old and in good cond.

To me it seems either bad AC clutch or weak auto tensioner could cause it, any help testing those components before throwing $100 parts at it?

Sounds like tensioner from your description. Loose belt slips and squeals on pulley with most resistance. Probably alt on start-up, then a/c when you activate it.
You could very carefully , and with another's assistance behind the wheel, vary tensioner pressure manually and repeat your test.

Have you had a good look at the belt itself?

Good morning Big Jim .

Does the belt have foreign material on it, such as oil, grease or coolant? Even though it is only a year old it can still be part of the problem. A good hard careful inspection is in order. I've seen a lot of nearly new belts squeel from someone getting carried away with belt dressing or grease. Sometimes a nearly new belt will need to be replaced and the pulleys cleaned. The problem can be as simple as coolant spilled on the belt.

If the belt checks out, then the tensioner is the next place I would look too.

Another test you might try is to yank the wheel back and forth to work the p/s pump harder, and see if that causes the belt to slip. If so, then its most likely as stated above. A belt with some grease/coolant or the tensioner needs adjustment. Good Luck.

I had the same symptoms you describe.
Took my car to the Ford dealer, though. They replaced every belt they could get their hands on, and that did nothing.

It wasn't until they replaced my water pump that the racket went away.

Seems strange to me, but I'm not even close to being a mechanic...

Also take a look at the idler tensioner pulley. If you can take the belt off, spin that pulley a bit and see if there's any amount of grab in it (It should spin very smoothly and freely). If you can feel anything grabbing hold, then replace it (They're only about $20). The bearings in those can go, I know from experience because my 98.5 Zetec with only 50k miles had the idler tensioner pulley go, and it made the belt squeal all day. Basically it's making the belt slip because the belt's grabbing on that pulley.

If you feel like changing it out, then I would suggest getting an odd-end ratchet with a 1/4 inch drive.

Well she's purring like a kitten again and you guys were spot-on. I planned to take off the belt and try spinning all the pulleys, check belt condition, pull the tensioner back and forth to see if it felt loose, etc. But when I went to release the tensioner to take the belt off, some plastic bits snapped off the tensioner and shot into my face. So it was a pretty easy call to replace the tensioner, the local dealer actually had the part, I convinced them not to charge me the $85 list price since I could get it for $61 online, and I was back in business under 2 hours.

For the record it takes a T40 torx socket to get the tensioner off, and I was able to get at it without removing anything else (except the belt of course).

Thanks for your helps.

Great! Sounds like something I will have to replace soon. Mine is making the same noise, only mine sounds like it is the top idler. I JUST replaced the alt and put a new belt on it. NO FUN. I will probably just start with the idler and then the tensioner (same day). If it isn't fixed, I will post some "real ticked" post (LOLOLOL) up in here cause probably the next pulley (one in the same general area) is the water pump!

If that be the case, anyone feel the need to join me? When I did the alternator, I already threatened to find a blow torch and make a major modification to the fender well....Just kidding.......or maybe not......

L8R
Rich