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Screeching Serpentine Belt

2002 Isuzu Axiom screeches when turned on. If AC on, AC works fine but car screeches almost all the time. Can hear me coming a mile away. If AC is off, car stops screeching once running a moment. My mechanic said more torque on serpentine belt when AC on so he changed serpentine belt a few months ago and currently belt appears to be moving fine. He says compressor operates fine. Started about 6 months ago right after new transmission put in at dealership under Isuzu warranty. Mechanic stumped and waiting for something to break.

If your mechanic did not replace the belt tensioner, then I would strongly suspect that a weak tensioner is the source of the problem.

Check your battery to see if it’s in good condition…A battery with a dead cell puts a big load on the alternator and its drive belt… Make sure all the pulleys are in alignment with each other. Next, replace the belt and its tensioner pulley. Next, carefully examine the crankshaft pulley for wear.

Get a new mechanic. A mechanic who is waiting for something to break is not acting in your best interest. There is no way to know for sure, but if the mechanical stuff is really OK then the problem is probably the belt and your mechanic doesn’t want to change it.

I wholeheartedly agree with VDC that the tensioner is an extremely likely cause.
I wholeheartedly agree with Caddyman that the other belt-driven components and their pulleys should be checked as well. The Axiom is a RWD, longitudinally mounted drivetrain, but it’s very possible that they moved something around and damaged a pulley bracket in a way that left it misaligned when they put your new engine in.

I wholeheartedly agree with MT that you should look for a new mechanic. Waiting for something to break is not a valid diagnostic technique for a symptom that can be readily verified.

I’m agreeable today.

I went through the same thing with a 2003 Toyota 4Runner when it was brand new. The serpentine belt was always chirping. The dealer replaced the belt and the problem started up again in a couple of days. The belt was replaced again. This time, not only did the chirp start up again in a couple of days, but the dealer’s mechanic didn’t put the belt on correctly and it pulled out the crankshaft oil seal. The dealer put in a new oil seal and a new serpentine belt. A couple of days later, the belt started chirping again. This time, I told the dealer he had one more opportunity to repair the car or he could buy it back under the lemon law. Furthermore, I was to be provided with a vehicle to drive while the 4Runner was being diagnosed and repaired. The service department finally found the problem–a weak spring in the belt tensioner.
It doesn’t seem to me that it would take a rocket scientist to figure this out. At any rate, once the problem was solved, I had no more problems. I have never been back to that dealer. I’ve had an independent shop do the servicing and kept all the records to keep the warranty in force. This dealer was 20 miles away from my home, but fortunately a new Toyota dealer went in about a mile away and so far, the service department seems very compentent.

Note that a bad BEARING in the tensioer can cause the noise too.