2000 Dodge Caravan AC Problem

In my auto tech class we are working on a 2000 Dodge caravan, 3 L V 6 and the symptoms are. When the vehicle is climbing a hill and kicks into passing gear the AC shuts off as it should but when it enguages the clutch slips and makes a bad squaling sound. It will eventually enguage but it drives you nuts until then. The compressor, clutch, expansion valve and drier are all new. Charged correctly with freon but the problem still presist. Any ideas or solutions would be appriciated. Anyone seen this same problem before?