My radiator fan won't stop running and have had it unplugged for the Minnesota winter -- now I'm going to be needing it as it is above freezing temps... where should I look first??

thanks in advance,
todd

I take it you mean the electric fan. Most likely someone has wired the fan so that it runs continuously when the key is on. Someone did this with my old 240D before I bought it. As an experiment, I unplugged it, and never found that it got hot enough to need it again. However, my AC was long since kaput, and although I floored it for hours at a time on long trips, I never drove in temperatures consistently in the triple digits.

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83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
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On most W123's, the aux fan is actuated by a temp switch on the receiver/drier. The switch could be stuck on or the relay could be stuck closed. Or the fan control could have been re-engineered.

Any idea how one would "unplug" a belt-driven fan?

has a place to unplug it as it comes around the radiator...so that's where I unplugged it....

Sorry, I think I got two threads on this going...but...anyway, shouldn't I be afraid of overheating the engine if I were not to fix the fan?

I unplugged the relay and it shut the fan off...I also pulled the #12 fuse and it also shut off the fan -- so, the TEMP SWITCH has got to be shot, right?

My question is this -- where is the temp switch and where is the receiver/dryer?

THANKS

that relay seems to work fine -- since I can hear it click on/off each time I plug it in and out....so that seems to be OK -- more reason for the temp switch to be the reason???

The aux fan relay on my 190E was clicking, but it was found out to be faulty.

The relay beside it is for the compressor. Switch the two and see if the auxiliary fans stop. If it is, the relay might be stuck on.

The auxiliary fans are triggered by two switches - the temp switch on the head which indicates it's too hot, and tells the fans to come on. The other switch is on the AC receiver/drier, which turns on the fans above a certain refrigerant temperature (like in stop & go traffic). The aux fan relay on the W123 is located on the driver fender beside the compressor relay (forgot which one, they're labeled 1 & 2 I think or 3 & 4).

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That is definitely not the case on some W123 models.

It would be nice if you could elaborate...

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Please refer to post #3.

that's the same color as my 79 wagon -- albeit slightly less glossy....not bad though for over 700k.

Anyway, I swapped both of the relays and they both kept the aux. fan running nonstop...so, I'm still a bit unsure where the heck the A/C temp switch is...are you saying it is in a black box directly or behind the receiver/dryer? I've also looked at performance and couldn't find the darn part...

If it is that black box...I did pop that open the other day to look at the connections in there..seemed OK...but obviously I'm not exactly sure what is what...

thanks

The switch is on the receiver/drier, which is located behind the right headlight. No black box is involved.

Would you like a picture?

http://catalog.peachparts.com/ShopByVehicle.epc?q=1979-Mercedes--Benz-300td-Climate--Control&yearid=1979%40%401979&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6228%3AED%7C10000132%3AMBC%7C2515%40%40300TD&catid=242213%40%40Climate+Control&subcatid=242240@@A%2FC+Temp%2E+Switch&mode=PD

If you have continuity through the switch when the car is cold, the switch is bad.

Are you saying that if the engine temp rises and the engine overheats, there is no provision for the engine to obtain additional cooling?

P/N 006-545-14-24 is an auxiliary fan switch rated at 212 degrees F (100 deg C). This is on top of the temperature switch at the AC drier, P/N 000-820-80-10, is the switch you are talking about earlier.

@Peachykeen: try disconnecting the temperature switch for the auxiliary fan on the AC drier (it has a pigtail with two spade connectors). This is ON the AC receiver drier. If this does not work, try the auxiliary fan switch on the head, this should be near the thermostat housing, on the passenger side of the engine, in front of the intake/exhaust manifolds.

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What I am saying is that on some W123 models the only mechanism involved in the actuation of the aux fan is the temp switch on the receiver/drier. That would seem to suggest that the aux fan was included in the design as an air conditioning component and not intended to function as a radiator fan.

Found the temp switch -- sorry I'm still learning...

Guess what -- it is plugged/attached nicely into the dryer/receiver....but the ends are NOT plugged into anything at all...

Next to it is a wire that runs the fan and at the ends has a cable connecting the two (i unplugged one end and it shut off the fan) ---thus, apparently making the fan run constantly...so, why haven't I noticed this fan running all the time?? I thought for sure it would only come on if hot...

Should I try and hook this all back together correctly? wonder why someone wanted to bypass the receiver/dryer??

strange...to me..

That would depend largely on whether or not you want the fan to work correctly.