Q: The car is overheating and hissing when the AC is on

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My car has started to overheat lately. When I drive with my air conditioning on, I start having problems if I come to a stop light for instance. The air turns from cool to warm and the hissing noise can be heard. Then, the engine starts overheating. I checked the level of coolant and it's fine. When I stopped my car in the traffic recently, it began to overheat but I pulled over and waited for it to cool down. Then it ran fine again. What could be the issue? Thanks.

Hello, if the car is only overheating when it is not moving then it is usually caused by an air flow issue through the radiator. Most of the time, this is caused by an issue with the radiator fan not coming on.

To diagnose this, I start by starting the engine and allowing it to warm up. As the engine starts to overheat the fan should come on. If it doesn’t, then the fan and the circuit need to be checked. Most of the time this is caused by a bad fan or fan relay. If you need to have this fixed, consider having a certified mechanic come to your home or office to diagnose your overheating problem accurately.

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