Q: My car only overheats when ac is on?

If you have overheating only when you have the A/C on then you most likely have a bad fan clutch. The fan clutch should lock up when the added heat from the A/C is added from the condenser to the radiator.

You should check for any blockage of the fins on the radiator or condenser. Also check the radiator for lack of coolant flow through some of the internal passages using a laser pointer type temperature probe to see if the radiator has hot and cold fins indicating partial blockage. You should try to flush out the radiator and replace the fan clutch.

If you decide to get this serviced, consider YourMechanic, as a certified professional can diagnose your overheating issue and help you make the necessary repairs. Good luck.