My car overheats when the ac is on. When I turn it off the temp goes back down.

Does it overheat driving down the road at 55 mph with A/C on?? ... Don't even need a fan then... Ram air takes care of that!!

If you have a fan on the condenser, you may want to make sure it is running when A/C is on..... Or your fan on the radiator is not running due to a faulty clutch fan if so equipped

I had this happen a couple times with my 2004 Santa Fe. I looked around on the Internet and finally found a solution. The radiator fan wasn't working because of a blown fuse. (I checked the fuse box in the engine compartment and the one under the dash. The one for the radiator fan was in the engine compartment.) I purchased a package of replacement fuses in different sizes (just to have on hand) for a couple of dollars. Once I replaced the blown fuse, the problem was solved!