Am trying to get all the functions to work on my 78, installed a new control head and discovered someone had cut some of the vacuum lines. Now while trying to run them down I find I have no vacuum to the system, the "round' canister on the right fender well is broken and I assume that is the source for the vacuum to the control head. First question am I right about this being the vacuum source and second my Haynes and Chilton's manuals are useless in this area so where can I get a good vacuum diagram for the 78??? By the way defrost and floor push air but not the dash vents.
Thanks for any help :dontknow:

The ball is actually a reservoir for vacuum, and operates the HVAC and sometimes cruise if you have that. A vacuum line runs from the manifold to the ball, with a check valve in the line to prevent loss of vacuum on acceleration, etc. You tee off that line between the check valve and the ball, and that vacuum runs into the cab to the heater controls. I think the line color is Pink. On AC models a second line runs back to the engine compartment from the HVAC controls to the heater Control Valve on the heater inlet line. Vacuum is applied to this valve when in Max AC, Max cool, to prevent the flow of hot water.

No vacuum going into your heater controls will prevent the dash vents from opening. Get that one squared away and see if it solves your problem.

Thanks, I was fairly sure that was my problem just not positive how it all plumed up -- thanks again