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.