Air flow: Vacuum vs mechanical

When you turn the dial to change where the air is coming from (which vents), how does the dial work, does it use vacuum or is it mechanial (cables, etc.). My friend said that her mustangs air will not get off of the windshield defroster mode, she turns the dial to regular but the air doens't come out of those vents..help. :eek7:

Yes its vacuum driven.

are there any hoses that commonly crack or break? she can't switch her ac to normal and its tooooo hot. can i get to the hoses for the ac w/o tearing the dash completely apart??

I doubt it, I'm working on getting rid of EFI stuff on my car and i have to down to the firewall on the inside. Hope I can put it back together! Seems like I remember there being a couple of vacuum lines running to a junction and a spring lookin thing just left of the glove box, you could possibly reach it from the bottom.