I have a 73 LT w/air. The plenum and kick-pad vaccuum "pods" are always in the open position regardless of the Temp control setting. The rest of the pods seem to be working OK for the other heat, Defrost, etc.. Can anyone offer advice on how to trouble-shoot problems with this vacuum operated Heat/AC system? I have the 73 Chevy Svc manual but it doesn't offer much help beyond the schematic. I'm not even sure when the plenum and kick-panel valves should be in the closed position? Suggestions? Thanks for the help.