squeaking drive belt

My '88 drive belt keeps squeaking when the AC is on, I have replace the belt and even went a notch shorter to make it tighter, but after a few weeks it starts squeaking again when the AC is on, could it be possible the tensioner is bad?? any ideas? thanks

bump.....

might be the actual ac pulley is going.

AC compressor clutch makes a tinging sound when it goes, trying getting a GatorBack serp belt. They are avaliable at autozone.