The low speed fan is not working on my 126 euro. Thanks to this forum I have narrowed the probable causes down to a faulty dropping relay. The problem is that I can't find it. It is not below the headlight (either one), as identified on many posts. Is this because a euro has it at another location?

The fan power and R/D sensor wires feed into a harness and run up under the fuse box and through the firewall. There are no signs of any wiring exiting this harness at this point. I can't tell how the wiring comes back through the firewall to the fuses and relays. Does anyone know where the dropping resistor is located?Please help me. Thanks.

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Don's 500SEL Euro

The "low speed" aux fan resistor on the W126 chassis is in the area of the brake booster. Somewhat hard to see & even harder to replace.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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Could anyone advise what is the easiest route for replacing the aux fan ballast resistor on an '86 300SDL? It looks like the master cylinder and resevoir may have to come out?

On another note, I mistakenly ordered an auxiliary fan switch from a supplier and received a single pole (red topped) 100 degree Centigrade switch. I'm not sure where this switch goes or does. The vendor said the MB part number is 006 545 1424 but couldn't tell me its installation location or exact function. No doubt, someone can set us straight on this.

The only switch I could find that looks similar is a 50 degree switch screwed into the block behind the water pump. I am told that switch adjusts transmission shifting characteristics.
Thanks for any advice.


Dave Jonas

'86 300SDL 138 k mi.
'84 300TD 240 k mi.

Thanks M.B.DOC,

The resistor was right where you said...under the brake booster.... and hard to see and harder to replace, as you said. On visual inspection it was obviously dead. The only way I could get it out was to take a long shafted screw driver and break the leads off. That allowed me to hook the two leads and pull them up to where I could just barely get connectors installed. Then I jumper wired the two leads, so the fan runs on high speed.

The car has never run better in this 105 degree Las Vegas heat. When I get the new resistor I'll relocate it to a more accessible place. Thank you so much for lending your expertise!

P.S. - Dave, I don't know if you want to try this "last resort" removal and replace methodology, but I honestly couldn't see any other practical way to do it.

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Don's 500SEL Euro

<
The car has never run better in this 105 degree Las Vegas heat. When I get the new resistor I'll relocate it to a more accessible place. >>

With the heat of Vegas, I would leave the jumper and forget the resistor..
More air flow and the added bonus of high speed fan draws less power.....

Thanks for your advise Arthur. I'll do it.

I should mention to any others that read this thread that I've also done the VFC mod, so between this and the mod my overheating in traffic days should be behind me. It's been a challenge here in Vegas where 115 degree weather will hit a few times each year (oh yea, but its a dry heat).

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Don's 500SEL Euro

I followed your advice and "cut" the resistor out of the circuit. Is there any reason to replace the "low speed" resistor other than a quieter fan?

Dave Jonas

300SDL
300TD

None that I know of..

I only mention doing that in extreme climates , as under normal thermal load conditions, it is not needed... but if you live in a high temp/humid inv. , the more air you can push , the better..
Specially at no/low ground speed... that is when you will note the difference... once the high side on an a/c unit gets in the danger zone [ meaning high head pressure ] , you not only get poor a/c efficiency and compresor pressure safety cut outs, but you also get over-heating of engine coolant temps cuz the damn /ac condenser is in front of the cooling radiator... passive heat transfer right where you don't want it....

I appreciate your expertise. I can't really say that I live an "extreme environment" as I'm virtually a neighbor of yours (Francestown, NH). The car in question is a new 300SDL for me that I purchased out in San Diego and had trucked to Boston. The body and interior are in great shape but mechanically I've developed a sizeable "punchlist" that I'm working my way through. It now appears that I will ultimately be facing the all too common head gasket/head replacement project sometime in the near future.

Thanks,

Dave

David,
Did not know you were next town up..
I run the Brick House Blues Room at the Pasta Loft in Milford..Stop by for a Beer and I will intro you to a customer/nieghbor of mine that owns the local Benz Indie shop.. Towne Lyne Motors, here in Amherst, NH ..
He is a great diesel guy and there are a bunch of Benz guys that hang here... if you see a white 250SL or Midnight E320 out front , I am in...
Arthur
Pasta Loft
Milford, NH

Arthur,

Thanks for the invitation. I'll be sure to stop in when I'm down your way.

Dave Jonas