What causes heat and AC to only come out of the defroster vents on a Ford Taurus Mercury Sable?

Answer 1

Answer

Make sure you have vacuum going into the cabin from the engine. The vacuum line runs from the intake manifold to a vacuum reservoir, which is a round plastic ball looking thing, then through more hoses through the firewall and into the cabin.

AnswerYou have an air management problem. The air management controls are vacuum operated and the default position is defrost. You probably have lost vacuum to the dash control unit, possibly due to a broken or pinched line running into the dash, or maybe a leaking vacuum canister. The only way to diagnose is to use a vacuum gauge and pump tester to go through the system from beginning to end, and see where your vacuum loss is.

Answer 2

a 5 cent broken hose that goes from engine through the firewall