i bought this car not too long ago for cheap and it came with a few problems. one of them is that the heat and a/c don't work. they don't even blow air at all. i'm not going to deal with a/c right now, but i'd like to get the heat going for the winter and perhaps just some vents blowing air from outside. anyone know where to start? here are a few things of note:

-nothing happens when heat or a/c turned on
-defrost does work
-there is no "servo" - what exactly does a servo do?

any advice appreciated. it's a 1978 300d non-turbo.

Sounds like a vacuum problem. I think default mode for a vacuum failure in the climate control is full defrost. Get a mighty vac, do some forum searches, and have fun.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

no servo? up front just behind the passengers headlight should be a 4" square box with a bunch of wires and hoses coming out of it... what do you have in this place?
the servo controls the a/c and the heat. and some other voodoo as well...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Ken, does your a/c control panel have round knobs to turn or a vertical row of pushbuttons? Does the blower work in defrost mode?

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If there is no servo that is the source of the problem, unless your car is a Euro with manual heat controls.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

it has a vertical row of pushbuttons and the defrost does blow. i read somewhere that you could somehow bypass the servo to just have the heat work. i just found it strange that the defrost does blow, but the others don't.

Was the car sitting??
You may have a nice mouse nest in the blow motor housing.

Also you may also have troubles with the blower motor regulator and temperature regulator.

Also you might want to remove the dash to see if anything has been tampered with. Working on a 83 300d now that someone cut wires and spliced that there own to go around the mercedes system. Needless to say its a headache and the other person work around didnt work.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

i think this car did sit for awhile. and i did find evidence of a mouse nest under a corner of the hood pad that was coming off, but haven't seen anything else. where exactly is the blower motor?

passenger side below the glove box. remove that cover

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

So last fall I got a used servo that looked to be in good shape. I installed it and have had working heat all winter. The problem is that no matter what I set the temp dial to, the air is extremely hot. However, the first day that I installed the servo, the temp dial did work. I got cool air, hot air, the a/c even worked. Since then, it has just been hot. Any idea what the problem might be?seems strange that it did work that one day.

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1980 300D, 128K