Why is my car overheating when the AC is on?

Answer by  Bala74 (26)

Your aux fan is not in movement on or if it is then it's not movement as accelerated as it should be. Screw the fan and the relay reliable method

Answer by  worker2349 (10)

The Air Conditioner Condenser radiates heat in front of the cooling radiator, and hot air from the Air Conditioner Won't cool the radiator, hence the overheat. May be you have too much antifreeze? Antifreeze does not cool. At most have a 50-50 mix. Minimum 80% water and 20% antifreeze more actual water the cooler it will run.

Answer by  worker8852 (129)

I have a 1998 Isuzu Rodeo that began to overheat about a year ago. I flushed the system and the problem went away. It is possible your thermostat is sticking, but a good flush should resolve the gunk that is making it stick. It is the cheapest fix to try first.

Answer by  Ralphie1954 (420)

Since your A/C unit takes heat from inside the vehicle and dumps it in front of the radiator, this decreases the cooling capacity of your radiator. Newer cars have an electric fan to increase air flow and some have a clutch fan which may be defective. Check these out.