When a/c or defroster is turned on, squealing sound and engine reves up. After a few seconds, sound stops and engine goes back to normal. a few minutes later it does it agin.

First thing though is to check if your serpentine belt that drives all those pulleys is stretched or worn

and that serpentine belt tensioner as well


in my case, the tensioner was failing at 90,000 miles & i replaced mine
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the tensioner is manually operated for the 2.4L 4cly engine and shares that belt with the alternator pulley

the tensioner of the v6 2.7L engine has that automatic spring-loaded unit

The first and second guy know what the are talking about . To save expense , get a new belt and bypass the AC unit. You won't have AC but you are still running

This caused by a locked up AC compressor or excessive AC compressor drag due to a defective compressor, this causes the belt squeal due to the excessive load, disconnect the electrical connector to the AC compressor until you can have this repaired or the belt will burn up and come off.

Sounds like a/c compressor starting to fail. hope this helps.