We have a Ford E 450 class C Motor home. Four Winds Chateau 2005. When you put a load on the engine the AC blows through the defroster instead of the dash vents. I know it's a vacuum line but how do you get to it?
Go to you tube and search e450 ac vacuum leak. Plenty of videos about it. I mounted the vacuum tank under the dash. Beats the heck out of disassembling the whole dash, and under hood. Ford didn't really think that problem through.