Auto Repair Help
Carl’s Corner – Auto Repair Help

By Carl O’Reilly

A loud squeal is produced when the A/C is turned on.

This symptom is usually caused by a loose or worn air conditioning compressor belt. When the A/C is activated the compressor is engaged. This places a load on the engine and the drive belt that rotates the compressor. If the belt is loose or worn the belt can slip on the compressor pulley and emit a loud squeal.

The drive belts should be inspected for proper tension and wear. A properly tensioned belt should have aproximately 1/2″ of deflection at its greatest span between pulleys. Inspect the belt for wear. Belts can become glazed on the inside drive surface which can cause them to slip, which produces the loud squeal. Some vehicles use an automatic tensioner that contains a large spring that keeps constant pressure on the belt. This system automatically tensions the belt to the proper tension. This system is often used on vehices that use a serpentine belt. This type of system uses one belt to drive many accessories.

Use caution when working around hot or rotating engine parts.

18 responses to “Loud Squeal When Air Conditioning Turned On”

  1. Hello Carl, Can loud squealing also be caused by a bad compressor,because I’ve had two vehicles when the compressor had to be replaced and each time there was a loud squeal when the a/c was turned on.So I was convinced that it was the compressor. Thanks for your response. Frank.

    • Jim silva says:

      I see a.lot of questions but no answers to all but the top question. How do you know it’s not the compressor not turning freely enough?

  2. Dan Gonzales says:

    It is a squall at the power steering pump the ac. is off I can bleed it.But the noise is still there when you turn the wheel the belts are not that old

  3. Dan Gonzales says:

    its on a Hyundai elantra with a 2.0 2006 model

  4. Cindy says:

    My husband has put on four compressors and done all the evacuations and freon. He has replaced idler pullly and belt, but each time they work perfect for about four months and then start the random squeaking/slipping sound. Any ideas of what could be going on.

    2005 town and Country Van.

    • Dawn says:

      Can a bad cooling fan clutch cause the belt to squeal? I have had the air compressor replaced and all new belts.I believe the fan clutch needs replaced because air conditioning has started getting warmer at idle but am trying to diagnose the squealing sound that sometimes happens when the air conditioning is turned on. Just wondering if they are related or should I be looking for other possible problems?

  5. Jun says:

    Hello Carl, thanks for the input. However, mine is a ford escape xls. Replacement of belt, the auto tensioner, ac Comp bearing and the other pulley was done but still i have the same problem…a loud squale when ac is on. Any idea please


  6. Pablo says:

    In my case it was a loose ac-alternator belt. Tightened it a bit more and that solve the problem. Thanks Carl!

  7. Felix says:

    I replaced belt and it still squeal

  8. Gary Cooper says:

    My compressor squeals when I turn it on Is it the compressor or the clutch

  9. Domo says:

    Hi I have a Bmw320d and have belt Squeal Changed Belt, Bearings ect and still have Squeal, Help please.

  10. Kierre says:

    My ac didn’t start squealing until after I had the belt changed? What can be the reason for that?

  11. Angie Kingery says:

    My 2009 Toyota Yaris. I just replaced a broken serpientine belt, it was squealing before it broke about 6 months. Now the squealing is even louder, only when I turn on the air. Help me please with diagnosis.. the right one!!

  12. Keith Smith says:

    New 383 stroker engine, new A/C, new belt on serpentine system. Everything works fine until I turn the A/C on then it starts squealing and the A/C will repeatedly turn off and on. There is no idler on this system.

    I’m not certain that it is the belt squealing. It could be the clutch. How can I tell which?

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