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Old 05-04-2003, 05:17 PM
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Thumbs up typical hi-temp, manual fan switch override implemented. whoo-ho!

I’ve read SO many posts complaining about the hi-temp condition associated with MB fan control. I feel your pain and share your sentiment, and decided to do something about my malady.

I just added a “manual override/control” circuit on one of my bikes and hope to do same on my W202.

We’ve all heard the complaint many times: the auto fan circuit is typically too late to engage for many’s taste. Sitting in traffic , eyes glued to the raising gage , wishing the fan was on NOW , anxiously awaiting the breeze

I’ve seen the excellent work posted here (cant remember who to credit) on the lowering of the fan circuit temp through changing the resistor, but knew that what I wanted was MANUAL control (actually override) of the fan.

What I now have is this: an unmolested auto fan circuit, and a manual FAN ON override controlled by a switch.
Switch off = 100% stock auto temp fan. Switch on = fan ON now.
The beauty is in the simplicity. Approx $10 purchased a 2-position auto grade illuminated switch, roll of 16ga wire and an assortment of connectors. If anyone wants further details, just post request here and I can explain the circuit.

This bike (water cooled) seems to be quite susceptible to rapid heat buildup during low speed operation in high ambient temps. Stop and go traffic pushes the temp up quickly, and just as in the car, I was stuck wishing that the fan was on NOW and that the gage was declining, or at the very least stabilizing. The fan would always engage much later (higher temp) than my comfort level, and repeat at each painful long stop light.

NEXT STEPS- get the info to design a similar circuit for the W202, it cant be that hard! I want to keep the MB circuit intact (or at least easy to return to) and add a manual override switch to be used when desired.

I do not have a W202 wiring diagram, so if anyone does have it, I would REALLY appreciate a copy or description of the fan circuit in any manner you can provide it.

i hope this sparks some thoughts, - benton (now smiling)

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Old 05-04-2003, 08:09 PM
Registered User
Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
I was thinking the same thing for my w201 but just for the aux fan, the main fan works fine left alone, but when you got no a/c you can use the aux fan to do this. The easiest way would be to simply cut the wire from the relay and solder one from a switch that is in the cabin running through a fuse in the electrical center, just to be on the safe side. Then you can flip it on and off whenever you like and it will shut off just like all other parts when the ignition is off.

But I'd prefer not to touch the original circuit and implement something into it, however, since I'm not an electrician, I'm not sure how to do that yet, but one day I might sit down and figure it out just for the heck of it so I can switch my fan on and off cause by itself it never goes on.

1985 190E 2.3L - a constant project.
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Old 05-05-2003, 01:30 AM
W202 AMG
Join Date: Dec 2001
Location: Cocoa, FL
Posts: 67
I am having the same problem with my fans not turning on soon enough. It is a real annoyance seeming I live in Florida and the A/C is not cooling properly when I am at a stand still. Please let me know if you come up with a something, I really need a solution for my fan dilemma.

Regards, Christopher

'98 C280 White on Tan

-=Santa Bring me a C43=-
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