Question:Climate Control

[reddog]

1982 300SD. Only way to get heat to the floor is by pushing button B. (two white arrows) If button C or D is pushed, leg flap door slowly closes. Starting from right side button E. Push button D and heat comes out left and right vents and defroster vents, nothing to floor. Button C, same thing, except AC pump runs. Have replaced temperature regulator, climate control unit in dash, and have gone through all the trouble shooting chapters in the manuel, and can find nothing showing the problem I have. I also went through the online manuels looking for an answer, and could find nothing. fg