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Cars & Vehicles
Heating Ventilating and Air Conditioning

When turning on heat to defrost window - cool air comes out - why?

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Wiki User
September 14, 2011 9:50AM

sounds like you have an air lock in your water works that's not letting the water flow from the engine through the heater matrix. check system for leaks top up and blead as required. if you have no visable leaks get the system pressure tested, could be something more serious developing.