In my '95 Aerostar, a problem has arisen. No matter what position I place the air control dial (on the dashboard) to (that is: heat, vent, defrost, A/C, etc.), the air will come only through the defrost slots.
Vacuum leak is likely, but it could be a LOT more places. I had a problem with my old 90 taurus where the air would shift what vent it was coming out of at idle when i hit the gas. It turned out to be a leaking vacuum motor in the HVAC system.
It helps to have a OEM Ford EVTSM manual that shows the hose layouts and what connects to what. And a handheld vacuum pump.
Look under the dash on the passenger side, and make sure the linkage is still hooked up, I know on some of the fords, they use a cheap plastic clip to hold it in place and it can fall off.
Thanks to all three of you for your helpful advice.
I looked under the hood after reading Don's note. I went and looked under the hood. I noticed a gap in the air-flow path, between the fan and the duct the fan feeds into. There was a pile of curmbly looking rubber or spongelike stuff below.
Not wanting to get into this, I took it on down to my local Ford dealership (Bluffton, SC).
They diagnosed and made the needed repairs. They told me a mouse, or rat, or some other creature had eaten through the gasket, or lining, or patch connecting the fan motor to the duct above, and had entered the cavity and had chewed into the vacuum hose that some of you have mentioned. They fixed both breaches, and now all is well.
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