If someone could please help, I have a 1977 Mercedes 300D that will get hot air through the defrost vent when in defrost mode, but no air at all coming through any of the other vents...the compressor kicks on with the a/c switch, but just no air whatsoever out of the vents.

i am working on a 77 240 se i am having the same symptons as you are. i posted alomost the same as you and got no results. BUT, i discovered a box /valve on the passenger side by the firewall has a bunch of wire looms and about 20 vac hoses coming out of it. it was so corroded and froze up that was junk. it has a rotary vac valve in it and a bunch of gears like a clock ,they work the blend air doors vor the vent a and also the hot water . the water valve is the bottom half. i have one ordered for this one. better be sitting down when you get the price. hope this helps .....digger

Well the expensive prices for parts sure doesn't surprise me...hehe...but the Mercedes is a really good piece of work. Right now I have the entire console out of the car as I was testing the vacuum switches. So far everything I've tried has worked, so not really sure what to test next. I found the switch you are referring to....up under the hood on the passenger side in front...just behind the pass. side headlight. Hoping you let me know if that is what fixes it. Also if anybody else has any suggestions, please let me know.

Also, there is a place online, *************** that seems really reasonable for parts. Think I will be using them more often.

mad scientist, it might be up by the headlight on the one you are working on. on this one it is back by the firewall. it has heater hoses going through the bottom. there is a plug with a whole bunch of hoses and a plug with a bunch of wires on it. i have a picture of it if you want . i havent figured out how to post it here.it is quite large like 4x5 inches and black plastic cover on top. 4 screws hold the cover on .the screw holes are sealed with black rtv.i will probly have it on by thursday .i will sure let you know how it went.....digger

hey mad scientist that heater control servo did the trick. got ac now. hope it works for you....Digger

Hey....was really, REALLY hoping that wasn't the problem. Glad you got it fixed, though. Thanks for the info!