I have a 1997 Jeep Cherokee, last summer we replaced the universal belt and power steering pump. Ran perfect until we went to turn on the AC or defrost then -insert ear piercing squeal. During winter months the squeal went away 100% when the defrost was used. Now that its summer the squeal is back. I have been told by several people that the belt is a) too tight and also b) too loose. Which is it or something else? Thanks
Have you checked the belt tension? The belt deflection can be measured and should be within spec. Or does this have an automatic tensioner?
My guess, however, might be that you need a new A/C clutch bearing. (The winter time quietness may have come from cooler and thus thicker grease in there).
You may want to add more details - such as the vehicle mileage, engine size, 2/4WD as others here may have something less like guesses and would need that info.