Belt Squeeling like a Mofo

[gumby002]

Hello
My belt squeals.
Here is what my observations are:
-Replaced Water pump & belt a few years ago
-Replaced Alternator 2 months ago
- Belt squeals when AC is on - I live in FL...AC button is always on
- With the hood up, I can see that the belt, when squealing, is not moving.
- Belt does not squeal when the AC light is off most of the time. If it does, its for 2-3 seconds only.
- AC does blow cold air, really cold, but it takes a minute or so of the squealing and then not squealing for the air to get cold

I am thinking that its the AC unit that is causing this. Its an uneducated guess because I've replaced 2 of the 4 pulleys/sheaves already.

Thoughts? Things I should try? Am i on the right track?
Thanks!
James