I have a 1992 Jetta 1.6L turbo diesel with AC.
The problem I am having is the heater controls are stuck in the dash position and I cannot switch them to defrost the windshield or to blow heat on my feet.
I have pulled the vacuum hoses off the back of the controller and one of the hoses does have vacuum. I put a small hose to this port and the other end to the other ports one at a time, and nothing seemed to happen.
My question is, is the controller the problem, or is it further on under the dash?
Any thoughts would be appreciated. :dunno:

The knob won't twist at all? If so, I would say that is a problem with the knob/pannel and not vacuum related. Were you able to turn the knob once you removed it from the dash and vacuum lines?

Sounds like there is a leak farther in not allowing it to change the position of the air deflector inside the dash that changes what vents it comes out of.