So the directional controller for the HVAC in my silverado won't seem to work on anything but windshield defrost. Think it could be the controller itself or maybe a vacuum ...

So the directional controller for the HVAC in my silverado won't seem to work on anything but windshield defrost. Think it could be the controller itself or maybe a vacuum problem behind the controller in the dash??
Any help would be greatly appreciated.

First off welcome to the site. I am gonna go with vacuum. I would start by tracing the lines under the hood. Also you may need to pull the dash apart and actually look at the control unit to make sure nothing has broken off the controler itself. I know my buddy had a 95 and thats what we had to do with his. If we can help you any more let us know

It's a vacuum problem. Vacuum controlled HVAC systems default to defrost when vacuum goes away. It's for safety reasons.

Ahhh thanks, that's what I figured. I have worked on alot of Chevy G Vans with HVAC problems quite simalar sometimes a vacuum problems others with other problems. I am a mechanic in the Air Force, only been doing it for about 3 years so I am still learning. Thanks guys, I am sure I will have other questions soon! Only owned my truck for about 2 weeks now and it seems some major TLC. Rocker panels, cab corners, door skins are rusted, fender well rust, the stepside has huge hole in it. engine oil leaks. (Planning on a new throttle body, intake manifold and some pretty valve covers.)