RV Repair: RV air conditioner problem, chevrolet g30, vacuum line

Question
Hello,
I hope you can help my husband and me with our AC problem.  We recently bought a 1983 Chevrolet G30 van.  When we turn on the AC, the air blows out of the defrost vent instead of the air vents.  My husband noticed a disconnected vacuum hose and connected it to a "stub" under the dash but that didn't solve the problem.   Can you give us an idea of what the problem may be?
Thanks for reading my question and for your help.
Debbie

Answer
I can help you I think.  On early Chevy cars and trucks, the selector on the dash was vacuum operated.  It directed vacuum to all the doors and vanes in the duct work.  If the loss of vacuum was to occur, the doors and vanes would "fail" in the defrost position.  This is because Defrost is the most important position, for safety reasons.  

That vacuum line you found under the dash is probably a good start.  It probably came off the back of the selector switch.  Did you check to see if any vacuum was present at that line?  If not, follow the line out to the engine compartment, or look along the firewall for a vacuum line that goes into the van.  This line could be dry rotted or cracked, or just pulled off the engine.  

The vacuum should plug into MAN (manifold) vac, similar to the brake booster.  If needed you could run a new line altogether.  Email me again if you need more help than this.  Good luck, maybe I will see you at the campground this summer:)