I have a 2001 Honda Civic Ex that has 85,000 miles. Everything works great until I turn on the heater. The heater air will intermittently just start to blow cool air then it starts to overheat. Have replaced thermostat, sensor, engine temp sensor, timing belt, water pump, radiator flushed, coolant level fine, heater core checked and cleaned, fan belts replaced, ac refrigerant charged...at wits end! I was told there is some sort of valve that is controlled by vacuum that allows the heated water into the heater core which then blows the warm air that could be faulty, but could that cause rest of engine to overheat and also to suddenly blow cool air instead of warm?
