Everything is working normally (the heat, the fan, air conditioning) but it will not switch off the defrost setting. It blows air out of the defrost no matter what the switch is turned to. Does anybody have any ideas what the problem is. I think it might be a vacuum problem, but I don't know how to fix it.
jerry

The defrost position is the "default" position.
You are correct, the deflector is vaccum controlled.
The source for the vaccum will be the upper intake manifold.....then there will be a "box" that holds some vaccum in "reserve" for when the engine is off.
In my '96, the vaccum is from the passenger side, rear of the upper intake manifold, and the reserve box is near the passenger side top of the strut, in the engine compartment.
Then a line goes from the reserve box, through the firewall, into the passenger compartment. The deflector, I think, is on the passenger side, up under the dash.
At least, that is where the sounds come from when I switch to the "off" position.
You can have a vaccum leak at any point in this path. Also, a pinched vaccum line.