How much pressure is in your a/c system with the a/c on? At the low side port by the battery the pressure should be about 30. If it's a hot day above 80 the clutch should stay engaged. Also, the system should have above 80psi at "rest" cool engine like if the car is parked overnight. My sister's Mystique had a worn clutch, but it worked at idle, would stop cooling at road speed.
