Vacuum Pod ?
 

My 85 300sd started blowing AC out defrost:( I do get some out of the two vents, by driver window and same for passenger side.
Vents good out the console for the back.

Could it be the one for main flap? If so where is it on the 126?
greazer2b

Start with checking the three behind the glove box liner, those go first as they always cycle as the car is turned on and off.

Front feet does not seem too fail often.

The one for the center vents is not that hard, you have to access it from inside the HVAC box to disconnect from the flap. I use George Murphy's diaphragms to rebuild all the single tit ones.