W140 aux fans dead, where is controller/module? 1996 S420 - PeachParts Mercedes-Benz Forum

wildirishtime · #1 07-25-2006, 07:47 PM

I have been reading for hours on the groups and can't
find any detailed info on where the controller and/or resistors
are located. Please don't give me a quickie answer....
I've looked between the two fans, on the framerail behind
the leftside headlight, can't find anything. The two wires
that go from each fan drop into the same wire loom and
dissapear towards the fusebox.

Here's my story. I purchased this car and it seemed to run
fine at normal temperature.... i dont recall the aux fans
turning on ever for sure. But then one COOL 60 degree evening
my temp gauge started bouncing around the redzone when
on the freeway and past the redzone so i turned around and went home.

At these temperatures 125c+ I never see the aux fans turn on when
testing sitting in my shop.
I ran 12v to them and watched the temperature drop magically
to 115degC and stabilize so I'm sure they need to run, and
something isn't letting them.

Now this S420 has been abused and various things have
been removed like the AC compressor and left out for some strange
reason.... now everything I've read says the fans run by
AC pressure AND by temperature. BUT... the question is..... if
my compressor is out (or even in other cars in theory if their
AC pressure was low our out of coolant) will the fans stop working
in that condition EVEN THOUGH the engine temperature is high?

Second question.... which exact temperature sensor is used for
this fan system on my 96? There's no resistors in the front of my
cooling fans and the webpage that shows the 'temperature modification'
using a resistor shows a temp sensor with two connectors...... but
mine only has one and when unplugged stops reading dash temperature.
So..... is that the same sensor that runs the fans on mine?

Thanks for your help, i'm really feeling stumped and that I don't know
where to go.

Thanks,
-Brendan

Matt L · #2 07-25-2006, 09:32 PM

MY96 is supposed to have the N65/1, behind the left headlamp. I believe that it gets its signal from N22. If so, you should be able to hold both AUTO buttons for >10 seconds to demand full-power from the fans.

N22 gets the ECT from the instrument panel on the 210, and I suspect the same is true of your car. At least when it was made...

Which brings up a huge caveat. My 210 uses a N65 to control the fan (it's in the fusebox). Later 210's used the N65/1. Later still use a N76, fed by N10-1 in the module box, rather than by N22. If I needed a new N65 from Mercedes, I would instead have to buy N76 and N10-1 for about $800. Your car may have similar updates which have been applied. Or broken parts which must be updated.

Gilly · #3 07-25-2006, 11:17 PM

Sorry to give a quickie answer, but what you need to do is find the electrical schematic for the aux fans on this model. You seem like a smart enough guy to get to the root of the problem if you had the diagram. I'd concentrate your efforts on locating that first.
Gilly

wildirishtime · #4 07-25-2006, 11:39 PM

I really need to know locations though cause I can reverse engineer most wiring myself if I can get my hands on the relays/resistors/module, but I admit wiring schematics would be helpful if anyone knows where to get them for the W140, please let me know.

-Brendan

pcmaher · #5 07-26-2006, 09:00 AM

Alldatadiy.com has good schematics for the W140. Check out the Alldata description on my web page.

mbdoc · #6 07-26-2006, 09:09 AM

On the left frame rail less than a foot from the bottom of the radiator...good luck.