190E Aux fan-stays on all the time
 

I searched the threads but most of the postings were regarding the Aux fan not coming on. My stays on all the time. I did wash the engine over the weekend so is this result from soaking the sensor on the engine?

I stopped the fan from coming on by pulling the single connector from the sensor farthest forward on the engine.

Is this sensor bad or is something else triggering the Aux fan? It runs fast and is very loud (high speed?).

Thank you in advance,

Haasman

Here is the sensor picture with the wire detached ....

Hi Haasman,

could the sensor/connector be wet and it shorts around the connection? May be drying and dielectric grease?

Good luck

Reinhard Kreutzer

Come to think of it, I think you can test the sensor with a digital meter for continuity, i.e if resistance is close to 0, sensor is bad.

Reinhard Kreutzer

Reinhard

Thanks for the replies. I did try and dry it and I am letting it sit after running.

Regarding testing it: There are three connectors, the one I pulled off to stop the fan. Is this the one that should be tested?

Haasman

Hi Haasman,

let me first say I don't have your car and I am not the world's greatest electrician either, but here is my attempt:
from your picture, it looks like the wire you have taken off brings the electricity to the switch, so I would test that for current. The other 2 should not have current. Then I assume the current will flow out through one of the other pins, depending on the temp. So I would test for continuity between the pin you have exposed now and the other 2. If you have zero resistance, that would mean that current would always flow through that wire (and that wire hopefully goes to the fan motor).

Your picture also seems to show some insulation missing to the right.

I hope I am not leading you into the wrong direction. Any other "electricians" out there feel free to chime in.

Reinhard Kreutzer

If you just washed the engine . . . you got WATER in the sensor.

It will take a week or so for it to dry out . . . Once it dries . . . Take some silicone and SEAL the seam where the BRASS crimps around the PLASTIC . . .

Thank you Reinhard. I believe that the disconnected sensor wire connects to a relay which directs the power to the fan. The fan consumes a lot of power and the relay could not handle all of that juice.

What I am trying to understand is there something else in the circuit which would tell it to go on, such as a faulty high-pressure sensor on the AC or something.

Regarding the wire that looks like it has insulation coming off, it is actually the brown covering, but in this bad picture it looks like bare copper. See the second picture.

mpnye- I will wait a week and see if it dries out. That sounds like a good possibility. If so, I will dress it with silicone.

Thanks for the replies all. I will update the post when it starts behaving itself again or another solution is found.

Haasman

Hi again,

on my 126 there is a pressure switch at the ac unit and it looks like the attached picture on the driverside front of the car.

But mpnye has it probably right and the water might dry out. While it's wet, it should show 0 resistance though...:D

The engine temp is what makes the fan come on at high speed.

The AC switch makes the fan come on at low speed only.

Gilly

RKreutzer

The 0 resistance is measure between the single-pole on the sensor and ground?

Haasman

My '91 190e has a similar problem, although I didn't wash the engine. The Aux fan will come on high even when the engine is cold started and the A/C is off. :confused: The A/C has been converted to 134a (before I bought it) and I know that the 134a operates at a higher pressure than the old r12, but would this cause the fan to come on even with the A/C switched off and engine cold??

Here in the desert of So. Calif. I modify the wiring at the Aux. Fan Resistor so ALL the wires are connected TOGETHER so the Aux. Fan runs on HIGH for the A/C High Pressure Switch to reduce HIGH SIDE PRESSURE . . .

Definitely the sensor is your problem
 

Hi Hassman,

If you get 0.0 Ohm from the single pole to ground then the sensor is shorted. When the sensor is cold you should get Mega to infinity Ohm.
This sensor properly gonna cost you around 50 bucks. And don't worry about other things because you said it, when you remove the connector to the single pole the Auxilary fan stops!

Thanks 16VAlex and everyone for your replies.

I always learn things on this site!

Haasman