Iliri and Lashquat, sounds like y'all have main cooling fan issues. When you turn on the A/C this starts pumping more heat into the radiator as the condenser is in front of the radiator, which results in the temp rise since your main fan isn't pulling any air to compensate. For an inexpensive replacement just check a few local junk/salvage yards and get a replacment from a Trooper that had the 3.5L engine. Changing the fan takes about 1/2 an hour and is pretty straighforward.