Ventilation Problem

Hello everyone. I am new to posting here, but have relied on this forum many times in the past for fixing automobile problems I have had. I now have a new one that has me stumped. I have a 2000 Windstar that will only put out air from the defrost vents on top of the dash. The air conditioning and heat both work, but no matter what selection I choose-top vents, floor vents, Max AC...whatever-the air only comes out the defrost vents. What is causing this and how can I fix it. Thanks in advance.

Brian

The heat/ac blend door is electrically actuated on your model. But all directional doors are pneumatically actuated. There are three such doors. They are all supplied their vacuum signals from the heat/ac controller rotating switch ... the one you twist.

You may have lost the vacuum supply to this control switch.

The source for the vaccum is from the back (firewall side) of the upper intake manifold. There are a lot of lines that connect back there, that provide a number of different functions.
The line that provides vaccum to the directional doors goes to a "box" that holds vaccum, then a line goes into the passenger compartment.
The vaccum is then distributed to the various (there are several) doors that control where the air goes. You could start at the selector switch, and follow the lines from there.

You might be able to locate a leak by a hissing sound.

It is possible that a line has become disconnected, developed a leak, or gotten pinched or hot, clogging it.