have vacuum @ hose going thru fire wall next to a/c, but no vacuum @ heat/ a/c / def. selector switch. any ideas? also what is the vacuum line going thru fire wall just under vent intake grille? both vacuum lines I am discussing are on passenger side.

 

Trace that line and visually inspect. Sounds like it is kinked/blocked/melted.

 

it disappears thru firewall how do inspect it what dissassembly would be required to access it?

 

You will have to find out where iot comes out in the engine compartment. Usually lots of poking around with a telescoping mirror and a flashlight.