Ford Repair: Explorer climate control, engine vacuum, vent air

Question
I am getting air blowing out of only the defroster vents.  When switching the selector switch (and it does "feel" like it is moving normally) to the vents or bottom vent air output does not change.  Is the controled by engine vacuum?  Does it sound like a disconnected or damaged vacuum hose?  How does the dash pannel covering this area come off?
1999 Ford Explorer 4 door,4X4 with airconditioning  and about 120,000 miles.

thanks,
John

Answer
I would check to see if its a vacume leak nearest to the engine compartment. You can buy a can of leak detector, spray this on the lines and the leak will show up. Removing the dash is a big job, you can start by removing the selector switches first, for the heater, defrost. You also can check underneath the dash. Thanks..