How can I check the electric cooling fans? I've never had them come on without the air being on. Now that my air has conked out, how can I test them to be sure they are not the culprit? New resistor was installed in April by Stuttgart South in Nashville

electric cooling fans are for the aircon only when switched on they come on

The aux fans come on high speed when the coolant temp reaches 105C.. can be tested by removing the connector on the blue 2 wire switch on the thermostat housing. They will come on when that circuit is open.
The a/c uses the low speed fan [ pre-resistor circuit ] and comes on when the high side pressure of the a/c reaches 20 bar.... that can be tested by jumping the high pressure switch at the drier/reciever
Two different circuits using the same fan/fans...

this depends on if it has a viscous fan

It does
He has a 201.029 w/103 engine

Also,he already had the preresistor changed out , so that indicates dual fan circuits ...ECT/AC........

thanks...now, where is the thermostat housing? do you mean the coolant thermostat housing(I know where that is) or something different...sorry, mb's are still quite new to me. VW's and Chevy's I'm used to.

I've looked for a blue wire but can't find it...today my coolant reached pretty close to 105c and the fans didn't come on...I need to check them out.

If no blue switch at thermo housing, then you have a green 3 wire switch , if so, unplug it and jumper to ground the br/gy wire to ground.. that should trigger fans

is not , check fuse "D" -16A..
There were a few changes on the sensors and fans on these models.
..but , NONE of them trigger until 105C, so don't expect fans til then.
[ except for low , a/c fan]

the only things I can find sticking out of my cylinder head top are a blue sensor with green and brown wires and a green sensor with black/green and pink/green
wires (it's hard to tell if it's black/green or black/yellow and pink/green or pink/yellow)...and a black sensor with one black wire. None with 3 wires. When my a/c was working the fans worked fine...but it's locked up now and I just want to be safe and know they will still come on because they aren't running now without the ac. I'm One of those anal retentive people

As stated in a prevoius post , if you have a BLUE SENSOR/2 WIRE.. dicsconnect it and see if the fan comes ON

Your reply to my BLUE 2 wire sensor was you could not find a BLUE WIRE .. there is NO blue wire , BLUE is the color of the base of the proper sensor..

I'll let that be my next shot tomorrow...but it's still not at the thermo housing..it's kind of towards the back of the engine...that's why I couldn't figure it out. My diesel chevy is much easier to find stuff on...

On the '89 190e-2.6 it should be under the edge of the air-filter box..
So, that is where to do the high fan testing...

I unplugged the 2 wire connector from the blue sensor and the fans did NOT come on...what next?

I also tried jumping the two wire connector...no fans...that way either.

Did you try Fuse "D" , 16 A as previous post mentions ?
If that is OK , you need to check wire diagram