Outside air always blows - vacuum leak?

[kiato4]

Hi all:
The defroster vents on my 1994 LWB always blow air no matter what (and it increases the faster I drive). Is this a vacuum leak of some sort? I've checked the vacuum reservoir under the hood but it looks like the hose has no crack. Where else can I look? Is it possible it's the right vertical slider switch on the heater control that needs replacing (the footwell/defroster control)? Thanks.

[OkieRover]

The flaps in the heater/air box are a mix of vacuum and wire controlled.
I think there is only one vacuum one though. So the fresh air flap is open and feeding the defrost vents. You should be able to move that air to the feet with the controls.

[kiato4]

Unfortunately, no matter what I do, even with the air always on the feet, it still blows outside air. It must be the fresh air flap I take it?

[OkieRover]

Yep.
The scoop right near the windshield at the back of the hood. That's the fresh air intake. Unfortunately it's not very pleasant to work on the heater box due to the dash having to come out.
If you have to pull the heater box out. Go ahead and swap your heater core while you have it out and replace the hoses. You'll thank me later.