Aux fan operation 190E W201

[crhenkel]

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