Why is my 2003 ford f150 make a.squeaking noise when i turn on the ac?

I have a 2003 ford f150 v6 4.2 and when I start it up the serpentine belt squeals, only for about 2 seconds then it stops. The only other time it makes that noise is when I turn on the a/c. I was told it could be the tensioner, but I don't want to just buy the part without getting other opinions.

When the a/c is on, it puts extra stress on the belt. It's one of 2 things. Your belt is wore out, or the tensioner is bad. Either way, both items should be replaced. Your problem should be cured after that.

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