The car overheats when the air conditioner is on.
The car overheats, is this the radiator fan? on 2007 Dodge Grand Caravan
Running the engine with the A/C on will raise the temperature for sure. Check to see that the fans are on when the A/C is on. If not then that's where I would start. It's also important to check the coolant level (when cold) and make a good visual inspection for anything that could cause overheating (coolant leaks, blocked air flow to the radiator etc).