Hi, working on a astro van & the dash panel will not change the defrost/floor/vent doors. The fan speeds work as does the ac & heater & blend door. Just can't select floor or defrost or vent positions for air flow. I'm thinking its the dash panel controls? Any help would be appreciated. Thanks
There is a vacuum control valve on the back of the control head that switches vacuum to allow mode changes. I'm not really familiar with that particular control but it might have another for rear operation. Check all of your vacuum lines. You know I just looked again and it's an '01, not a 91. I'll add this to my list of things I have to check on the office computer (alldata and mitchell). I'll get back to you if someone else doesn't answer first. Seeya.
If it's stuck on defrost, then it may be a broken vacuum line.
G.M. Tech and Ignacio will be the guys that know.
If it's what I think it is, I have a tip in the the Knowledge Base that shows where a common vaccum line problem is. Pictures are of a 98', which I think is the same as 2001. Someone correct me if I'm wrong. I know 2000 models still have this vacuum line problem.
I've not had one stuck on all three positions. Like something quit working during transition. This may not be the vacuum problem like I was thinking. When you loose vacuum I think you get 100% defrost only.
Do let us know what you find. Maybe GM tech or Nacho will chime in here.