My car is 1966 Skylark with factory AC. Its got the two slider switches, one controlling Hot or Cold, and the other controlling Defrost, Heat, or AC. Hot + Defrost= Radiant heat from the defrost vents, no air pressure. Hot + Heat= Nothing. Hot + AC= Hot air from AC vents. The AC works fine in any position. What gives? Something not routing right inside the dash? ~Mike '66 Skylark 340-4
Mike, my book says your car's heat and a/c is controlled by vacuum. The first thing I'd do is start under the hood and start looking for leaks. A hose could be off or cracked. There will be a hose from the manifold to a canister/tank. I'd start at the manifold and work my way into the car. There's also a vacuum controlled water valve in the heater hose under the hood. Leaks can be in any of the hoses, the actuators under the dash or at the vacuum switch itself.