Well, it's been over 100 the last few days so I didn't get a chance to try anything. But I went out today and started with the basics. I looked at the fuse for the aux fan, first it was the wrong fuse, a white 8 amp. I took it out, and the metal literally fell out of the fuse. I replaced it with a red 16 amp. Turned AC on while idling and the AC seems to do fine at idle. I have to do a test drive to really prove this out.

My question is, when I press the AC switch, should the aux fan turn on immediately? And stay on as long as the AC switch is pressed?

Thanks

No, not always depending on the high side pressure. there are 2 pressure switches on the air dryer. I know this has been mentioned above
One is the high pressure/low pressure cutoff. This switch only controls the compressor and will turn the compressor off if the pressure is too high, as well as if the Freon charge is low; it will not allow the compressor to turn on.

the 2nd switch is the low speed fan switch. (on my w126 for example), it turns on at 20bar(290psi); and enables the low speed fan. And it turns off at 15 bar (218psi). So your system high side pressure will need to be atleast 290psi for it to even enable. Which is a typical operating pressure after about 15-30sec of running. Then it will turn off once pressures drop below 218psi... (usualy when you are driving down the road on a avg temp day).

Not knowing the exact wiring setup on your w201, but it triggers a relay which passes thru a "preresistor" to give the electric fan slower speed.

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Just my MB's:
1990 420sel - Winter DD - 410,000km
1990 560sel - absolutely showroom mint - 360,000km!

No, the aux. fan will only operate when needed either by the aux. fan temp switch, or the high pressure switch on the receiver/drier.

That fuse is the first thing I would have checked, maybe that was your problem having the wrong/defective white fuse. I purchased our '93 190E new and about a year ago I replace every fuse in the car with new ones.

Report back with your test results, you might have just saved yourself some unnecessary expenses.

Good luck

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Interesting! Well, while idling my AC never got warm!! It stayed cool idling at a light and when I pulled over for about 5 to 7 minutes. It definitely was running colder while driving than idling, but not near enough to make it uncomfortable. In fact I could have sworn that while I was pulled over and idling it felt like the AC got a little colder! It could be my wishful thinking too! I expect a 4 cylinder at idle to not cool as well at speed, but is that normal?

Thanks!!!

It really depends on the conditions. At idle, do you hear the aux. fan cycling?
Hope you found your problem.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

I've actually watched and heard the fan at idle! So yes to answer your question.

Great! Thanks for posting your findings, it might help someone else in the future.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

I hope so. Thank you all for your input.