Dreaded broken driver's side footwell flap
 

As with most W126s my 85 300SD had great heat for the passenger but my feet would freeze. I decided to try to take care of it by using the suggestions on the forum.
1) First find a medium binder clip.
2) Detach the driver's side kick panel under the steering wheel
3) Reach in the hole for the heater box and open the flap (it should be totally free if not it isn't broken)
4) Insert the binder clip to lip that the door hinges on. It will snap into place and be slightly tilted toward the flap. It will keep the flap open and can be removed later on if you want
5) Replace kick panel
First set of pictures:

Second set of pictures
 

Here is the clip in place and how it looks

What would be the proper way to fix this problem? Is it caused by a bad vacuum element?

Proper way
 

This is one of the many easy ways. The footwell flaps are interconnected through linkage from the footwell vacuum pod. Unfortunately it seems the driver 's side seems to brake leading to the great heat on the pax side but nothing on the driver's as the air pressure keeps that flap closed. The proper way to fix it would be to take the heater box out and replace the flap. If you look on EPC you can see where it is located long with the repair kit for the linkages. The weekest spot it the chain is the top of the flap where it connects to the linkage. I verified that it was indeed the top of the flap where it connects to the linkage by using a mirror to look up at the top and see a part of it rotating as the heat came on. I have to eventually repair the evaporator so I will save the repair until then and of course get two new flaps.