i'll bet this has been covered many times, although i myself am new to the group. i ask you: why can't we control heat ourselves? we are qualified to drive the car, can iwe not handle controlling the heating or cooling of said vehicle?
last night it was a mild evening here in denver; the climate control could not be controlled. the fan was going on frequently, constantly blowing hot air in my dry eyes. swtiching back and forth between cool and hot, lots of fan and no fan, etc. much like i would expect a "climate control" system to behave. tonight, after the cold front has moved in, i get nothing. the fan went on when i started the car (blowing cold air because the engine was cold). then it went off about the time the engine warmed up. no sign from the fan after that. my fingers were numb and my nose was cold. i had a little heat trickling out of the drivers side dash vent depending on how fast i was going (but it does that when the heat is off and the controller set to "min.") i would like to be able to sit in may car without a heavy coat, hat, gloves and wool socks please! the heat was malfunctioning like this when i picked it up about this time last week... not nearly enough heat on a cold night, fan never came on. i drove over 20 miles and the fan didn't make a peep, i could see my breath inside the car when i arrived home. for the last few days the "system" seems to have worked properly (with the exception of no floorboard heat). now it decides to die, right when the cold temps and snow are on their way. i know, i know, use the search feature. i will, i just needed to vent, because my car won't its going to be a could couple of days outside trying to fix this thing.

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1982 Mercedes 300 SD

on Mercedes electrical problems.
Replace all fuses with NEW.
If the issue is still there, go to further diagnosis.

What was engine temperature???
The CC will not allow blower to come on if engine is below 30C...

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ASE Master Mechanic
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Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
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Technical Quality Auditor.
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1985 300SD
1983 300D
2003 Volvo V70

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I have an 85300SD. I think the systems are very close. I experienced same problem, it turned out to be vacuumed control issue. It cost me about $10 to fix it the next time up after spending $200 with a specialist.
2 places may cause the problem. The electronic control or the vacuum control. I will first check the vaccum control and see if that is the problem. First, you have to hear the air flow gates open or close when you move from Max cold to Max warm. If you hear that you have vaccum inside the system. Next you have to see if during climate control the correct gates open. To do so you will need to access the vacuum controls located on the passenger side under the central console. Sit on the passenger side, put your hand on your left knee, move your hand to left until you hit the inside/underneath the console, that is where the valves are. Will need to remove the padding. The vacuum system is in serial layout about 8-10 units mounted on a metal strip. The top one normally works perfectly.
2: Electrical "brain" of the Climate control system (the push buttons) you can remove and change it completely, can buy a used one from many junkyards for about $80. Simple to change, will need to remove the ashtray, remove screws inside the ashtray, then with small Screw driver (flat tip) push the emergency blinker switches and all other out (pray them out carefully) them remove the console, There are two screws holding the control in place, Remove and change unit

i was told that about the defroster. no such luck with mine.

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1982 Mercedes 300 SD

Hey Jimmy : Mine is a 1980 300 SD.so dont know if this applies to your machine. Mine has a double pole relay that makes the CC system default to the defrost function even if theres no vacuum at all. The defrost function gives max heat at max blower speed. It will at least keep you from freezing. The vac system seems to be a weakness for these cars. wish you luck. Willie(Poor Soul)

That sounds like a bad monovalve diaphragm issue along with an ACC that needs soldering. Both are easy.

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1984 300D Turbo - 4-speed manual conversion, mid-level resto

1983 300D - parts car

1979 300TD Auto - Parts car.

1985 300D Auto - Wrecked/Parts.


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"If you don't know where you are going, any road will get you there". Lewis Carrol