W140 aux fans dead, where is controller/module? 1996 S420

[wildirishtime]

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]

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]

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]

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]

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

[mbdoc]

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

[wildirishtime]

Can you please elaborate? Is this the controller or the actual resistors that I should see? What does it look like? How big is it? What does the connector look like? I found a box in that general area but assuming I typed the part numbers in right it came back as some other controller device, can't remember the name.

I'm stumped enough from the minimal amount of direct answers in other threads that I (and other future W140 owners) need a little more clear info on this.... thanks a bunch!

~B

[Matt L]

I'm not positive, but I'm fairly certain that there are no resistors to limit the fan power. This happens in the controller, which is integrated into the car's electronics in one of a few possible ways. As I said, N65/1 should be fed from the pushbutton control module N22 (if that's what you have in there). N65/1 is not extremely large, but bigger than a standard relay.

[mbdoc]

TRY this picture..again under the car on left frame rail..

[wildirishtime]

OK so here's my update and I'm even more confused.. first off please
remember my aux cooling fans were totally dead.. no pulsing on or off,
no slowness, just DEAD:

I went under the car and found the module with the five conductor
plug as DOC pictured in the previous post. 12V, brown ground, two heavy
colored wires (one to each fan), and one brown lightweight line at pin
5. I verified 12v & ground. Tested for resistance on the colored wires
back to each fan, nearly 0ohms. Jumped 12V line to the colored wires and
verified their operations down at the plug. All appears good
in the wiring.

Plugged the module back in, got in the car and held the two AUTO
buttons down for about 8seconds and the fans turn on high.....
if I watch that lightweight wire on pin5 with my voltmeter it sits at 0v
when the engine's off or running, but when I turn on the
fans with the dual-AUTO button trick it jumps to 8v (when engine
off) and 11v (when same test is done with engine running).
PLEASE REMEMBER MY ORIGINAL POST where
I said that some idiot before me pulled the AC compressor
so I have no AC system if this has any bearing on my problem... it's
my understanding pressure and temperature are tested seperately....but
I don't know anything for sure!

Here's the problem: If I keep monitoring voltage on pin5, and i get
the car hot (clear up into the red) I never see any voltage (stays 0v)
on pin5..... therefor I'd assume, if I'm right, that something isn't
signaling the pulse module to turn on?

So is my test accurate? I have read that on the 210's that they use
current signaling to the pulse module.... but I get 0volts with a 125c+
engine on the lightweight brown wire on pin5 of the connector...
doesn't that sound like a problem and am I correct that I have proven
no problem exists in my pulse module??????

Please point me in the next direction... must I monitor current inline
on the pin5 and watch for the 2ma to 10ma current draw I saw listed
on some other thread I read? Or is my voltage test indicative of
an upstream problem?

Last question: I saw someone describing that possibly the pulse
module has the ability to sense overly high current draw in the fans
and shut itself down... is this a possibility? how can I test for this
problem? I tried running each fan seperately and neither activate
when temp is in the red.

When the AUTO button trick turns on they run forever with no
problems until I turn them off with the key. Please help I don't know what to
test next and dont know forsure my tests are accurate. If anyone
has a schematic of what's upstream from the pulse module that would
be awesome as well!

~Brendan

[Matt L]

Originally Posted by wildirishtime

When the AUTO button trick turns on they run forever with no
problems until I turn them off with the key. Please help I don't know what to
test next and dont know forsure my tests are accurate. If anyone
has a schematic of what's upstream from the pulse module that would
be awesome as well!

~Brendan

Ok, now you're getting somewhere. N22 will tell N65/1 to run the fans.

It would appear that N22 is not getting the ECT signal. It comes from the instrument panel on the 210, and I suspect the same on your car. So it would seem to be one of these:

(1) N22
(2) Instrument panel
(3) Connection from the instrument panel to N22. It's a serial link on the MY96 210, but I'm not sure about your car.

What you can do now is read the current-sensor values on N22. With the key in position 2, hold the REST button for >5 seconds, until the display changes. The left side shows the code you're reading, the right side is the value, and you scroll through them with the AUTO keys. Write down the values and report back.

[wildirishtime]

Originally Posted by Matt L

The left side shows the code you're reading, the right side is the value, and you scroll through them with the AUTO keys. Write down the values and report back.

Here are the codes, can you send me a URL that explains them all
while you are at it? Or a link to a thread that discusses the codes, that would be appreciated as I couldn't find a complete list on the forum.

Here we go, this is the results when the engine is cool and NOT running:

1-107
2-125
3-103
4-104
5-105
6-145
7-0
8-122
9-0
10-0
12-4.2
20-0
21-0
22-0
23-0
24-12.3
40-5
41-3
42-1
43-130

The following CHANGED when running at 80degc:

1-105
6-151
8-121
12-4.3
21-7
24-14.3

The following changed between not running (cold) and Red Zone temp:

1-105
5-104
6-205
8-126
12-4.3
21-27
24-14.4

Thanks for your help! Looking forward to your responces!

~Brendan

[Matt L]

Hotter than **** there right now? Ok, here's what the climate-control manual says:

1-107 : in-car temp sensor
2-125 : oustide temp sensor
3-103 : left heater core temp
4-104 : right heater core temp
5-105 : evaporator temp
6-145 : ECT
7-0 : high-side refridgerant pressure in bar
8-122 : high-side temp
9-0 : not used
10-0 : blower control voltage
12-4.2 : sun sonser
20-0 : current for auxiliary fan
21-0 : engine speed
22-0 : vehicle speed (kpm)
23-0 : terminal 58d in % battery voltage (and I have no idea what that means)
24-12.3 : battery voltage
40-5 : Software status
41-3 : Hardware status
42-1 : version code 1
43-130 : version code 2

The following CHANGED when running at 80degc:

1-105
6-151 : ECT
8-121 : Refridgerant high-side temp
12-4.3
21-7
24-14.3

The following changed between not running (cold) and Red Zone temp:

1-105
5-104
6-205 : ECT
8-126 : Refridgerant temp
12-4.3
21-27
24-14.4

----

205 is just barely high enough to run the fan on the 210 E300, and not in the red on that car or yours. If you're showing the red zone and N22 shows 205, there's a problem in one of the systems. Perhaps your engine isn't really overheating after all. Maybe your dashboard gauge is wrong.

[wildirishtime]

The temperature indicator 'bounces' at times, but I didn't
bring it up because it isn't as drastic as others have explained
from loose connections while driving... it still acts 'linearly' when
it gets hot, and when I manually force the fans on the temperature
drops and holds today (nearly 100deg outside) to 115c on the dash,
but will bounce up and down 15-20degc within 1/4 second and then
stabilize again... slightly erattic, maybe a sign of a problem, but
to verify I must know the readings on Code #6 to double-check if
the fans SHOULD be turning on yet right?

I have replaced that temperature sensor with one terminal that resides
just above the water pump.... I did that first out of the box thinking
I had a sensor problem causing the 'boucing' and questionable overheating problem but that wasn't it. I admit I have no symptoms of overheating
except the dash pegging into the red and no fans turning on automatically
when the temp gauge reads in the red.

Can anyone else verify this code #6 entry? Anyone know what
temperatures coincide with these values so as to cross-check the
fan switch-on temperatures?

Thanks!
~Brendan