My reference threads I was looking at are

Main air flap? Why??

and

W123. My experience with replacing all AC vacuum elements without removing the dash.

My '85 wagon will not pull in the main air flap, and it causes the center vents to close after a while. I can push it a little {removed glove box} and as long as I push it left {open} to start out, the vac will pull it over and keep it there and the center vents remain open.
I guess I need to pull it apart and check the diaphram, but I just can't figure out the functions of the two flaps mentioned above.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John