I believe the footwell flap actuator to be on the drivers side up against the firewall and behind the center section of the dash (if you know what I mean). remove teh kick panel and then dig in under there and you should find it.

vent flap actuator is accessable through the glovebox as i remember. it is on the very top of everything under teh dash I think... To remove the glove box there are several small pins that insert into plugs that fit into the box edges around the front side. Using a small screwdriver pry teh little plastic pins out of the plugs. Both surfaces are on the inside of the box. I don't know how else to explain it but once you do one it will make total sense.
Then remove the light fixture by pulling/prying inward and disconnecting the wires. You can now pull the entire interior of the glove box out.
Gosh, I sure hope this isn't the way to the defrost vents... Sorry if I am having a senior moment here.
I fairly recently helped a friend on his 85 and I may be remembering his layout.

Are you chasing your vacuum lines with a MityVac? I had one line that went to the acc control unit that had a bad rubber connector and this was at the root of all my problems, I thought. After I fixed this all my flaps etc worked but no heat still. That's when I figured out that it was the servo on my car.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique