Hot air from vents while moving

[L82Vette]

I have a 77, when the car is moving I get hot air that comes out of the heater vents, does anybody have any ideas about what could be wrong? :confused

Thanks Lou

 

[mfendley]

2 thoughts

Your heater control valve is leaking by (either the vacuum singal to the valve is not adequate to shut the valve, or the valve is old and is allowing water to pass) or the seals around the heater core housings are allowing hot air from the engine compartment into the passenger compartment.