Any quick fix for footwell heat?

My 79 300SD/116 (almost always) has no heat to the footwells regardless of which button is pushed on the climate control panel. The car holds vacuum well (for days!), so I think a vac-operated airflow routing door is sticking or something. Is there an easy way to rig something that would allow heat to enter the footwells? I suspect there's a way I could just work the door(s) by hand and free it up, but I have no idea where to look! As a matter of fact, I can't even figure out where the footwell airflow is supposed to come out!

The aforementioned (previous post) gal-pal is complaining- and hot air blasting on her face and torso from the windshield and dash vents is not helping. I used to be able to close the center and side dash vents with the levers and squeeze some heat out below, but no more! There is plenty of warm air in the plenum, and the blower works fine, air just won't come out down low. A full repair will eventually happen, what I need now is some info on how to access those doors and/or their actuators/linkage for a little manual "persuasion".

This is a classy beater, not a restoration project. Crude temporary fixes are welcome...

Thanks in advance, Dave Larson

[Silver Boat]

Sounds like a vacuum leak or bad control valve. You may be able to get under the dash and prop the heater flaps open until the proper fix can be found. You will only have heat though and will not be able to turn up the defroster so it may not be a good idea. Should not be to hard to find the leak if you are in there. The center dash vents will always be cold air, at least on my W126. Good luck sounds like my wife. She is always complaining about not having enough heat. She turns the house heat up to 85++ and wonders why we run out oil so fast.

If it's like an '85, don't push hard on the flaps! They are closed with a vacuum diaphram that's spring loaded. (normally closed). If you push hard you will break the ends of the flaps off (sounds like the words of experience?!) That's a real booger to fix.

Check the vacuum to the diaphram. If vacuum opens the flaps then the switchover valve that sends vacuum to the diaphram may be bad. Make sure you have 11+ volts to the switchover valve. If no voltage, check CCU.