Q: When I turn ac on it overheats

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I have a 2008 ford focus two door coupe. When its a hot day out, I have my ac on full blast, when im sitting at a light my air starts to get hot, then my car starts to overheat. But when I start driving again the air cools down and the temperature gauge goes back to the middle white line. It will do that a few times before it starts just overheating. When its more towards night time and its not so hot out, my car works just fine, I can have the ac on and it doesnt give me any trouble. Please help. Ive tried the thermostat, the water pump the radiator hose. Im starting to lose hope.

My car has 4400 miles.
My car has an automatic transmission.

Your car is equipped with an electric radiator fan. It should come on when the engine reaches a certain temperature. It should also come on immediately when you turn the air conditioning on. While on the move, the fan does not need to run but when driving at low speeds or stopped, it should be running.

It sounds like your fan is not coming on at all. That can be caused by a number of things:

  • bad coolant temperature sensor
  • bad fan relay
  • bad fan motor
  • bad ECU (unlikely)

You may want to have a professional diagnose your AC system issue properly, rather than just start changing parts because that can get expensive.

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