1992 190E 2.3 Temp/Fan Switch/Sensor Questions
 

l searched for a while trying to find the answers to my questions, but I couldn't find anything entirely definitive. My questions have to do with my new to me 1992 190E 2.3 that I picked up for a mere $500.

The electromagnetic fan engages just like it's suppose to when I jump the connector for the temperature switch at the cylinder head (the one with 3 pins, two for fan engagement and one for the gauge). So, I ran the car and waited until the temperature rose to 110 degrees Celsius at which point the fan locked up and cooled the engine down to 100 degrees, then unlocked.

I was confused a bit by this because I thought that the electromagnetic fan was suppose to lock up at 100 degrees and unlock at 90 degrees. Am I wrong? If I am wrong and it's working correctly, then I'd like to add a resistor to the switch to make it cut in 10 degrees early.

Also, I noticed that the high speed auxiliary fan switch (or what I presume the high speed aux. fan switch is) does not kick in the high speed fan until 130 degrees! A little too late to help at that point in my opinion. Does anyone know which resistor I could add to the switch to lower the cut in point from 130 degrees to 110 degrees? The switch in question is light blue and located on the cylinder head next to the above mentioned switch. When I jump the pins on the connector, it turned the aux. fan on at high speed.

Another problem regarding the aux. fan is that it will run on high speed randomly, even with the light blue switch mentioned above unplugged. So, I figure the problem must lie with a relay or another switch that I don't know about.

Also, what is the purpose of the temperature switch on the water pump?

Sorry this is a bit long winded. Thanks in advance.

The coolant temperature sensor on my W201 has a four pin arrangement - one side is for the gauge in the dash the other is for the ignition / fuel "computers". There's mention of a two pin sensor in the FSM - I don't think I've read about a 3 pin...

Have you checked the measured resistances of the sensors and compared them with the expected in the FSM?

I also have a 4 pin plug on my car. I thought that sensor was just for the ignition and fuel injections systems, but I am new to gasoline Mercedes... I usually work on diesels, so I am probably mistaken.

I haven't measured the resistance of any of the sensors/switches. I am having trouble finding the resistance values for the temperature switches. Anyone happen to know them off hand?

Also, the temp. sensor for the ignition and fuel injection seems to be working well, as the car is running smoothly.

After consulting the service manual, I found that the electromagnetic fan is functioning properly. Apparently, M102 engines fitted with air conditioning had a switch that triggered the fan to lock up at 110 degrees while M102 engines without air conditioning were fitted with a switch that locked up the fan at 100 degrees. However, they don't seem to be interchangeable since the one for A/C cars has 3 pins while the one for cars without A/C has 2 pins.

Another interesting thing is that on A/C equipped cars, the manual states that the aux. fan is suppose to run whenever the electromagnetic fan is engaged. This is accomplished by a "double-contact relay which is activated by the triple temperature switch" according to the manual.

Look in the engine electrical chapter for the data - but bear in mind it is temperature dependant!

The test for the four pin coolant sensor is to make sure the diagonal measured resistance is the same.

"Another problem regarding the aux. fan is that it will run on high speed randomly, even with the light blue switch mentioned above unplugged. So, I figure the problem must lie with a relay or another switch that I don't know about."

There is a pressure switch on the A/C receiver/drier that operates the Aux. fans when the high side pressure gets too high to cool the condensor.
FYI, there is a Aux. fan relay mounted in the rear of the fuse box. When mine went bad it caused the Aux. fan to run continuously due to the relay contacts fusing together.

They are thermoswitch and is an on/off device. The have a bi-metal inside. Adding a resister will not lower the cut-in temperature. You need a lower spec switch. I do not know your car well but the design should be generic across all old MBZ.

Electromagnetic switch - 110C is right if it is spec'ed for 110C. I think a 100C thermoswitch is red color. Yours may be grey or blue color.

Aux fan switch - It is triggered in 2 places. By the thermostat switch on top of the cylinder block ( may be by the same switch for the e-fan for high speed ) and by the recv/drier ( A/C, in this case pressure switch ) for low speed.

Hope this help.

So, I have done more research into the temperature switch arrangement on my 190E and I'm still a little confused.

I know that the black top 3 pin switch controls the clutch fan with 2 of the pins on it and the 3rd pin is for the temperature gauge. I know that it's for the temp. gauge because when I unplugged it the needle on the gauge drops to the bottom.

I ordered a repacement switch that is suppose to work the same, but lock the fan clutch at 100 C instead of 110 C.

My car also has a blue 2 pin switch that when I jump the 2 pins together, it will run the fans on high speed. I'm no longer sure if that is all it does or if it is also the A/C cut-out switch. I'm also unsure of what temp. it activates.

Then there is the sender on the water pump which I think has something to do with the automatic transmission.

It seems that the switches/sensors that are used on this car are different than any of the others that I've seen in the workshop manuals or anywhere else online. It would seem that during the early 90's Mercedes changed things quite frequently.

Anyway, does anyone have the same setup and do you know what switch does what and at what temp.? I just want to be sure that it's all working correctly and that I don't overheat the car as I live in a part of California that gets pretty hot in summer.

Still can't figure this out...
 

So, I put in a new switch (Part # 006-545-91-24 same as the old one) that was suppose to lock the fan clutch at 100 C, but it still is locking at 110 C instead.

It's not a case of a bad temp. sender for the gauge either because on this particular temp. switch, the 3rd pin is used for the gauge while the other 2 pins are used for activating the fan clutch.

What could be causing the fan to activate exactly 10 C higher than what the switch is rated at? Unless, I am mistaken and the number stamped on the side of the switch doesn't have anything to do with the temp. that it activates at.

I also tried using another switch (Part #006-545-42-24) that I know activates at 100 C because it came out of my friend's '85 190D, but didn't want to run the engine until the fan activated since the 3rd pin is a switch and doesn't work with the gauge, so I couldn't keep track of the engine temp.

Anyone have any input on why this is happening?