Max AC not working on Chevy Workhorse chassis

[jmpollack]

My dash AC was recharged by my RV shop last year and it produced cool air well enough since this procedure. That said, I noticed this week that when on Max AC no air comes out of the vents at all. What should I look for as the root cause?

Thanks in advance for your help.

[Dougflas]

loss of vacuum from supply to control head. It might help if you added the year to your post.