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Squealing/screeching noise when turning on air conditioner

hello, I am new to the site and would like to share what I’m dealing with, with the hope I can get some good advice or answers. A little over a month ago my battery died and I ended up having to get the battery installed one day and the alternator installed the very next day. After the alternator was installed, I started my car up and when I eventually turned the Air conditioner on, it started making a screeching/squealing type noise. I was first told it was the belt needed some lubrication but that didn’t help. I was later told the ac compressor was bad so I had it replaced. The mechanic thought he ordered a bad compressor so he ordered a new one and installed it…it was quiet for about 2 days but then it started squealing again. the sound was not as bad as before through but it was slowly getting worst. I took it back and he then told me the altenator was causing the problem on the ac compressor so I again I had the altenator replaced…no change. He also replaced the belt and no change. at this point we don’t know what’s causing it and I was hoping you could help. thanks

Belt tensioner , idler pulley , etc , something that belt turns is not spinning freely would be my guess or tensioner needs replaced .

Am I correct in determining the same shop has had four chances to solve one problem, and has failed in all four attempts?

…or has it been five attempts?

At this point you need to find a new shop/mechanic, because going back to the same mechanic expecting better results meets the popular definition of insanity (repeating the same process expecting different results).

It could be a number of things, some of which were already mentioned in the post above.

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here is a good video to start looking…

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yes you are correct. My next step is to take it to another shop. but they did not charge me for the additional labor or parts as they were trying to troubleshoot the problem. so I was giving the them benefit of the doubt to avoid spending more money somewhere else.

Sounds like an old Grand Cherokee with a 4.0L engine. The belt is loose, tighten the belt.

on the other hand…a belt too tight can cause all sort of problems, i.e. bending the shaft of the alternator causing the windings inside to make contact and quickly ruin it.