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Q: Cooling Fans

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What makes the cooling fans kick on only when the AC is turned on ? My fiancee's car is overheating when the AC is not on. I have replaced the radiator hoses and thermostat previously and just replaced the coolant temp sensor today. What else could it be causing this ?

My car has 137000 miles.
My car has an automatic transmission.

The engine fans should turn on based on engine temperature. If the sensors you just replaced are not connected properly, it would cause them to fail. When repairs have been made recently, always verify they are holding. Have you checked the water pump? If it is not pushing enough fluid through, the cooling system will not function.

Assuming the coolant is topped off and in good condition (old coolant has a lesser heat transfer properties), you may want to look into the fan clutch which controls the fan. This is usually replaced with the water pump. The other component you should consider is the drive belts. If the pulleys or the belt have failed, the accessories will not work correctly.

If you need to have this repaired, consider YourMechanic, as one of our mobile technicians can come to your home or office to diagnose your overheating issue firsthand.

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