As I understanding it bridging the switch with a 1.1k resistor will cause it to turn on early at 90C.

I tried this on a 2.3 with the red switch for the electro magnectic main fan (see pic below) and it doesn't work. Does anybody have an idea why this could be?

My guess is this mod only works for the switch for the aux fan which comes on at two speeds low and high.

Just wanted to add to the knowledge base so if you know the answer let me know.

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I do not believe that sw is a thermistor sw , but rather just a temp on/off sw.
The resistor will only work on a thermistor sensor because it changes the
resistance of the sensor [ with parellel resistance] in relation to temp.
This new resistance just puts the sensors values out of spec enough to create an earlier cut-in of the fan circuit.
Out of calibration, but to ones own liking...

An interesting side note to this..
The only reason this resistor bridging will work on these thermistor sensors is b/c the sensors are of the Negative Temp Coefficient design.. meaning , as the temp increases, the resistance decreases.. and when one puts two or more resistors together in parellel, the total resistance also decreases [ei. is always less than any single resistor]. So , you now can change the resistance value of a sensor to have less resistance at a lower temp than the original resistance at that same temp, thereby changing the values of the sensor and allowing for lower temp activation of the fans.
Many think that this fools the control module , but the control mod just works like it was designed .. it is the upsetting of the relationship of temp/resistance specs of the sensor that have been changed/fooled.

Got it. As usual Arthur thanks for your intelligent response

Yal
If you give a model/year , I can tell you for sure if your sw is a thermistor or standard temp sw.
..or, you can just put an ohm meter across it and see if you get a resisance value. A standard sw will just give you an open/closed reading..

I had a 190E many years ago and I think it's a switch; use an ohmmeter and you'll know.

Calibration is not a proper choice here: The varistors are not calibrated. They are measured as they are manufactured and those that measure within a set tolerance band are ok as usable in the car. That's why some aux fans kick in early (lower temp) that others.

Not sure what's interesting about that. . . it's been well defined on my web page as that's how it operates. BTW, if a varistor exhibited a postive temp coef, then a parallel resistor would still work. Hint: the operation would be reversed.

Again that's how the Cool Harness operates. From the point of the Control Module, it is "fooled". Of course, it's just a figure of speech, don't take it literally as you have done.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Thanks guys!

Arthur - I think its a switch. I have an multimeter and i'll check it out this weekend.
From what I can see, the two pin switches like the red one I show above and the blue one that looks like it, are switches that won't work with a coolharness. I am wondering now if the black-grey 3 pin switch that is on some 190's is the one that can work with the cool harness. If it is I'll get it and swap out my 2 pin one for it. I have no a/c so i'll just use the two pin side of the switch and leave the 3rd pin free. I don't know for sure.

I do know now that if you have a fan switch that does "double duty" i.e turn a fan on at low speed then kick it into high speed as the temp increases thats a switch that will work with the cool harness. The V8's have one on their auxilairy circuit for sure, and the cars with twin auxilliary a/c fans too. I can probably adapt one of these auxilliary switches to run my electro magnectic fan but I need to match the threaded shaft width so I can screw it into my head

Before anyone reading this asks...my cooling system is in great shape. I just hate the temperatures it was designed for!

< I just hate the temperatures it was designed for!
>

That is why I asked for year and model.
There was another switch on some models that came factory with a lower temp cut-in that just threads into your sensors hole
So , when you give me that . I can look it up for you..

PS .. don't confuse the dual fans of the 124 and 201 chassis with the S class fan set up.
These have 2 speeds , but they are independent of each other .. The low fan is a/c pressure activated and the high fan is coolant temp activated . Two completly different circuits that share the same fan motors .
The resistor bridging of the coolant sensor on these models only effects the cut-in of the high fan circuit and will never trigger a low fan.. that is only triggered when the a/c is on and the high side pressures call for fan via high side pressure sw.

. . is the one you want if you want to do the resistor mod or use my Cool Harness.

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__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Jim - No the blue one looks like this...
and is described as "Radiator/Auxiliary Fan Switch; Blue Insulator with 2 Prong Connector; 130 Degree C". It doesn't work with the cool harness so thats out.

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Arthur - Thanks. I figured it couldnt be that simply lol
My car is a 1988 190E 2.3.
Three things on the head...it has the two pin green sensor for the CIS, a black(?) sensor with two vacuum lines coming out of it (no idea what its for but its probably important) and a red two pin switch for the main fan, No A/C so no auxiliary fans, oh and of course the one pin sensor for the temp guage on the side. Thats It

Yal,
OK...
There was 4 production changes for that chassis.. but the main electro-magnetic fan is still standard type sensor [on/off -100C sw.] so, the change is to a lower temp/spec. sensor. There is a 95C and I will get you that part number.
The 3 prong sensor you mention for that chassis is the same type, but it is used for A/C equipped cars and has another set of contacts in the unit for a/c operation. [ again, on/off sw. with a/c cut-out 115C] But the fan side is still spec. 100C ,so that doesn't do you any good either.

Here is the ser # changes for your car during 1988.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1D00YU6RY1K00LNLOL&year=1988&make=MB&model=190-E-004&category=G&part=Auxiliary+Fan+Switch&appEngines=_any
The thermistor sensors are for aux fan/s circuits in front of radiator, so that is a different system all together.....nothing to do with electro/magnetic fan coupling sensors or circuits.

Great thank you! Let me know and I will walk down to Mercedes Manhattan to place the order for it. They are well stocked and order things from Germany quickly.

Is it located as shown in the attached picture or someplace else???

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Oh sorry...I don't know its not on my car. Some 190E's use it but not mine.

Hi Arthur - Were you able to find the part number for the 95C switch? Thanks.