92 Ford Crown Vic will not allow heat or A/C thru vents

My 1992 Crown Vic will not allow heated or cooled air to fully come out the ductwork. The A/C and heater plus the blower all work fine, but we can’t get it into the passenger compartment 100%. The control head (slider bar) has been replaced but this did not correct the problem. What needs to be done to fix this?

This vehicle is a little older than what I am used to. Mine has knobs and the controls are vacuum-actuated. You might have cables leading to the doors that control the air flow. The doors are probably broken or you have cables unhooked. I am not completely clear on the problem, however. If you get no response here, try www.crownvic.net. Be sure to say that this has slider controls. In addition, make more clear the air flow problem. Are you getting good flow at the defrost and floor, but the dash panel vents don’t get any air? In slightly newer Crown Vics, the first vacuum-operated door diverts air either to the panel vents on the one hand, or the defrosters and floor on the other. The second door has three positions and controls air flow between the floor and defrosters. There is a diagram at http://www.p71interceptor.com/eatcswap/. This information is not useful if the air flow is very different in the '92, but I doubt it is.

The system is what is called fail safe. When if fails, it fails in defrost mode so that the windshield will be clear. It would appear to me that one of the vacuum lines to a flapper door actuator has come loose, or the actuator motor is bad.

Assuming the air is flowing out the defroster vents, MG is almost certainly right. Even if you are not getting air out of those vents I would still start there.

If the air is not flowing out of the defrost vents, then could you explain why you say the A/C and heater and blower all work?