The owner' manual for my 1985 vanagon shows the ventilation panel with the
slides marked (top to bottom) A, B, C, and D.  The fan control is E.  Outlets
1 are for the windshield; outlets 2 are for the side windows; outlets 3 are
mid-level dash; outlets 4 are footwell.  The text is:

    Levers A and C - Air distribution
    Lever A at right - windshield (1) and side window (2) outlets open.
    Lever C at left - footwell outlets under dashboard (4) andfootwell outlets
in passenger compartment* open.

    Lever B - Temperature control
   To increase heat - slide lever to right. To decrease heat - slide lever to
left.

    Lever D - Roof outlets in passenger compartment*
   To increase outside air flow slide lever to left.
   To decrease outside air flow slide lever to right.

   *where applicable
   Fan control switch E
   The air volume can be regulated with three fan speed settings.

   Defogging and defrosting windshield and side windows
   Slide all control levers to the extreme right and turn fan control switch E
to speed setting 2.
   The fan control switch for the secondary heat exchanger should be OFF.

    Warming up vehicle interior quickly
   Slide levers A, B and D to extreme right.
   Slide lever C to extreme left.
   Close air outlets 3.
   Turn fan control switch E to speed setting 2.

   Warming up vehicle interior normally
   Once the windshield and side windows are clear and the vehicle interior is
warm, you may want to set the controls as follows:
     Slide lever A to the left.
     Slide lever B to desired temperature setting.
     Slide lever C toward center.
     Turn fan control switch E to speed setting 1.

    Outside air ventilation
    With lever B at extreme left, outside air is emitted from all open
outlets. When lever B is moved toward the right, outside air is emitted from
open dashboard vents (3)  only.

    Hints
    All operating controls, except fan control switch E and fan control switch
for the secondary heat exchanger can be adjusted to any intermediate position.
    Stale air is drawn out of the vehicle interior through vents on the inside
front door panels. The vents can be opened or closed by sliding the lever
forward or rearward.

That's it!  You're now an HVAC expert.