I need a bit of guidance in trouble shooting my wife's auxillary fan problem. The car is a 1990 190E 2.6. Runs like a champ on speed, but the engine seems to be getting progressivley warmer. Granted the weather here in central us is hot right now and she runs the AC all the time, but still, I see it getting hotter. The temp gauge is not coming close to the red line, but it just seems so hot...I am replacing the water temp sensor first to see if the gauge is working correctly. Is there a way to decide if the gauge is telling the correct temp to check it's opperation? I think the aux fan has a problem in the sensors or wiring. The fan does not seem to come on at the right times or at all. My MAIN question is: like many other I have worked on...is the aux fan supposed to come on and stay on when the AC is turned on? Most cars simply turn on the fans and leave them on when the AC is engaged due to the extra heat load. Mine are not coming on and staying on, some times hardly coming on at all w/ AC on. OR doing the intermittent on off on deal, which is likely much worse for the engine and the fan motors than smply staying on the whole time. I am replacing some of the engine temp sensors once they arrive...thanks Mercedesshop.
Christopher

The fans come on low speed (through a resistor) when the AC is at operating pressure (on at 20 bar, off at 15 bar, for what thats worth). They come on high when the coolant is at about 100 (watch your fingers.) If they are acting funny below 100 the AC might be low on pressure meaning low on freon. Search around here, its that time of the year for fan problems/solutions.

Do you have one of two fans, and if two are they both working (they are wired in parallel.)

Jim,
Thanks...that does help.. the 190E I have has the two elec fans and yes they are both working, just not as often as I think they should. And, they do not neccessarily turn on when the ac is turned on. I have seen the effects of the low and the hi speeds like you said. I rplaced the temp switch today and the result was not much different, however the AC is not particulary cold so maybe that could indicate the system is low on freon and then the pressure concept might be right on. What about the ac switch that is there on the ac freon system up front on the drivers side right in front of the ABS controls...could that ac switch be going bad? I think I might have teh ac seviced and try the pressure concept first.
Christopher