Just purchased 78 and the air blows out the bottom vents no matter where the control is placed. Is the control vacuum or mechanical? I have not had time to dig in yet, can anyone tell me what to look for?...Thank You

 

Check your controls for a leak or a loose vacuum hose. The "doors" that move the air flaps in the exchanger box are vacuum driven. The funky slider/valve/cam thingie on there is a real rube goldberg setup, and they do fail fairly often. New control units run about $100 or so (check ebay, ecklers, mid-america, etc.).

Also check the heater exchange box (if you can get to it) to make sure that the vacuum actuators are actually free and not stuck up with leaves, gunk, crud, rust, etc..

bill.