190E cooling fans run all the time! help. - PeachParts Mercedes-Benz Forum

bungy151 · #1 03-04-2007, 12:09 AM

I have a prolem with my cooling fans for my 1991 190E 8v.
The fans ( both the magnetic clutch cooling fan and the electric fan for the a/c) are always on, even at start up when the engine is cold.

The problem seems to be with the dual contact relay that when energised brings on both the cooling fans. It used to be that when the a/c was turned on, both fans would roar into operation, but now they both are on even when the a/c is off. I think it is a sensor or short in the wiring?

I have checked the operation when they are on and i pulled off the plug to the 100 degree C temp switch just behind the thermostat, and that did not stop them. I assume that this switch is ok. The only way to stop them was to pull the connector that goes to the a/c drier I think it is high side pressure switch, the one with the pigtails and white connectors. But I don't know why this is in cicuit with the a/c off?
I know that the electric fan for the a/c has 2 speeds and that there is a resistor near the headlight that gives the low speed it checked out ok, .4 ohms and no hot joints. Would there be a problem with the a/c pressure switch or the a/c relay. Some insight into the fan's operation would be appreciated.
David.

brewtoo · #2 03-04-2007, 12:20 AM

Since the fan stops when you disconnect the AC pressure switch it means the pressure switch is closed, and since the pressure switch should be open with the AC off, then the pressure switch must be bad, wouldn't you think?

bungy151 · #3 03-04-2007, 12:28 AM

Hello brewtoo,
Yes that does sound right, I will try and confirm this by testing with meter when the engine is running. I did read in another post that this can be a problem with water i.e engine wash down, and I did seem to remember that i did blow a fuse for the aux fan when we recently had a torrential rain.
Will check tomorrow and post results back. One good thing with this fault is that the engine temp and the a/c run very cool all the time, but I get bad economy.
David.

bungy151 · #4 03-05-2007, 03:28 PM

FANS STILL RUNNING!!!
I have checked the high side a/c pressure switch with the car running, and it did not switch at all.
And to my surprise when the a/c was turned on disconnecting the pressure switch this time did not stop the aux or electromagnetic cooling fan?

What else would be controlling these fans?

it seems that everytime I check to see why these fans are running there is a different scenario. Could this be a problem within the wiring loom, e.g. shorts etc. Is there a link between the a/c Klima relay and the dual contact fans relay? Any suggestions from an expert would be great.
David.

david s poole · #5 03-05-2007, 04:35 PM

the a/c pigtails only control the low speed fan operation.there is an o/heat switch in the waterjacket[close to thermostat] that brings on the fans at high speed.i think it is a blue two pin switch which when it either goes bad or is unplugged brings on the fans at full speed[imagine that,you don't have to o/heat your car to find out that the switch has died].

richard28 · #6 03-05-2007, 04:44 PM

Not intending to hijack this, but in checking the a/c pigtails on my 1987 300e this weekend as I followed this thread one of the spades broke off. Since my a/c doesnt work anyway, until I fix the a/c is there any harm in leaving the broken pigtail in place? Or should I just swap the part with the good one on my parts car? Thanks.

bungy151 · #7 03-06-2007, 03:00 AM

David s Poole
This could be the problem, do you know how to check this switch?
My coolant temp switch (if this is the same switch) is red in colour not blue, but probably does the same job and has 2 temps written on it one is 100 degrees c and the other is 107 degrees c.
It is by the way a 3 pin switch comprising of 2 pins that fit a 2 pin plug /connector, and a single pin that a single connector fits onto. Does anyone know what the 2 different switches do? I have pulled the plugs off these when the coolant fans are running, but this does not stop the fans.
I believe the 2 pin switch is the coolant 100 degree switch that activates the fan at high speed. Can anyone confirm this?
The pigtail at the connector would not hurt to be left as is if the a/c is not operative.
David.

ytr1903 · #8 03-06-2007, 09:30 AM

Have you tried pulling out the relay that energizes the aux fan? My 190D had the same problem as you have, it turned out to be a bad relay that was stuck in the energized position. Just swap relays with some other function and you will either find the fix or determine that I am wrong. Either way you are a little closer to finding your solution.

Tom

david s poole · #9 03-06-2007, 09:47 AM

i think you are correct in your assumptions and i think that the single pin on that switch is for shutting down the a/c in situations of o/heat[it goes to ground].the test for the two pins is to pull off plug and short the two wires together,if relay working properly this should shut the fans down.otherwise you are going to need to find the relay and replace it.

bungy151 · #10 03-07-2007, 02:24 AM

Fan problem continued
When the car is idling, and I turn on the a/c both fans start up, and they cycle on and off with the a/c compressor. The dual contact relay in the fuse box is what is controlling both fans. I know this because I felt the relay in operation and I can feel the relay click in and out when the compressor starts and stops.
I therefore think that the relay is ok. If I pull the relay out when this is all happening bingo the fans both stop. Somehow I think there is a signal gone a miss from maybe the a/c relay that tells the a/c compressor to start up, to the dual contact relay that controls both the cooling fans.
More investigation and checking needed.

David

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