In the attached pic the heating & cooling controls seem obvious, except for one. The right-hand rotary knob is stuck; the markings on the rim would suggest that it controls air flow, either up, down, both up & down, or ? (off?). Do other controls have to be in certain positions for the right-hand knob to be rotated? Does anyone have a user's manual that covers this?
1984 W126 Grey Market 280SE.

Attached Thumbnails