Hello, my car is running fine but when I turn my air on it runs through my top(defrost) vents. It still comes on at the correct temperature but won't come out my main vent. I would like to know what it could possibly be, cost, and the cons to it. Thank you.
We don't get involved with costs here because there's way too many variables, plus, we don't even know what needs to be repaired. Most likely you have vacuum-operated actuators and the vacuum hose feeding the system is broken or disconnected. Most heater systems are spring-loaded to go to the defrost mode when there's a vacuum problem. That's for safety. Your feet might freeze, but your windshield will be clear.