Heat from floor but not from dash on '76 300d

[PatricdeBoer]

hey all, I'm new to this forum but I've owned a 1976 300d for the last three years. I have been slowly but surely bringing it back to a somewhat restored state. There is one problem that I have been puzzled about for some tim. I can get hot air to blow from the foot vents, but non to come from the ddash or defroster, It just blows cold. If any one has a clue it as to what it could be it'd be appriciated.

[Lycoming-8]

The center vents should not blow air when in heat mode, but the two on the outside ends of the dash should blow hot air in heat mode. Usual cause is a failure in the vacuum operated pod that drives one of the flapper valves under the dash. Could also be the solenoid that drives the pod or a failure in the push button control unit. A mityvac is usually very helpful in diagnosing the problem if it is the vacuum issue. Use the search some more and you should see other posts on this issue.