6 Series Fresh Air Duct System - Ed Owens

In diagnosing a problem with my front a/c unit, I removed the dash to check on the operations of the fresh air doors between the heater blower and the interior.  Several people asked for pictures, so here is a compilation.

 

Control motor

Two air vent doors, closed.

 

Hereís whatís under the dash.  The air vent doors are closed.  These are controlled by a stepper motor on the right side.  These open forward, controlled by the center control vent (on my 87 M6).  The amount of opening is proportional to the lever position.

 

When the A/C is turned on, these vents close irrespective of the control panel lever, and the output from the A/C fan lifts two a/c vent doors.  These doors are closed by gravity when the a/c blower is off, and keep the heater from blowing backward through the a/c intake grill below the radio.

Retaining clip (1 of 2)

A/C air outlets, lifted by air pressure.

 

There are two clips that attach the surrounding duct to the underside of the dash.  If these arenít attached, there will be an air leak under the dash.  On my car, these clips hit the braces decending from the front sheet metal, making them hard to engage or disengage.  As a result, one of the retaining tabs on the underside of the dash broke off (damn!).