Was wondering what the purpose of the water temp. switch locacted on thermostat houseing is compared to temp. switch located on receiver drier as my auxillary fan was acting up in that it would make an attempt to start but would not start so I put it on a switch and activate when I want.I am going to be putting in a new drier shortly and was thinking if I could correct my fan problem with a new switch on the drier I would do it is this the sole switch that controls fan or does the other water temp. switch have some bearing on it also.Maybe there is no harm in leaving my auxillary fan on a toggle switch except that if I forget to shut it off when I shut down I could come back to a dead battery.

I'm not an expert in W126 electrics but the switch in the thermostat housing may be for high-speed aux fan and the one in the refrigerant may be for low-speed aux fan. It's that way in my '87 300D (W124) but I don't know how much similarity there is in the two models.

Jeremy

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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

an 85 SD has a 1 speed fan.

Those switches both control the aux fan. The one on the AC drier turns the fan on when refrigerant temp is 52C. The switch on the thermostat housing is 100C.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Not to knit pick but........ the fan is turned on by voltage either thru a droping resistor located near the dryer or around the droping resistor giving 2 fan speeds. One of the sensors on the dryer turns the fan on low speed and the other turns the ac off if the freon pressure is low IIRC. The fan is turned on high if the engine overheats by a sensor on the thermostat housing. Look at the wiring diag of the cd manual to be sure. Don't have a manual? Better get one .... they're about $20 or from MB. You're not likely to leave the fan on when you leave the car because it makes a lot of noise on low speed.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K