My 83 300D blows cold air for the first couple of minutes until the engine heats up. I thought I read that it was supposed to not blow air until the heating system came up. to temperature. I suspect the temperature sensor behind the ACC panel. Does anyone know if that sensor is simple a switch or is it a thermistor like the sensor in the dash. If it's a switch is it N.O. or N.C. when the car is cold. BTW everything else in the climate control seems to work OK Thanks Russ

If it's a bad sensor, I would think it is the one that tells how warm the coolant is and not the one behind the ACC panel which senses the temperature of the passenger compartment. It also could be a fault in the control panel itself.
It is designed to blow air at anytime in the defrost position.

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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

Where is the sensor that tells the coolant temperature? Also is the ambiant temperature sensor easy to locate?

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1982 300D Turbo "Helga"
380,000 miles

My TD does something similar. The fan comes on once the the engine temp reaches 40c. I was under the inpression that this is normal.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

I don't think the sensor in the center of the dash would cause this. It would, however, be very worthwhile to remove the glovebox and ensure that a hose is in place to feed sample air to the sensor. If it has not already been replaced, you will think that it was never installed. It was originally a foam hose that disintegrates. The best replacement is black pipe insulation material from Home Depot.

Good luck,

The sensor that monitors the inside temperature is located behind a vent in the center of the dash Location seems to vary with model & year. In my old 78 300D it was located in the right corner of the dash I think in the speaker grill. The H2O temperature sensor I think is located behind the ACC panel just below the electric switch over valves. I am pretty sure that is where my problem is. The system does a pretty good job at making the inside of the car comfortable oncethe water in the cooling system warms up ..... Russ