I would make sure that . . .
somebody who reads those sensors that can properly operate a ohmmeter, even if you have to do it yourself. If you not able, maybe you can enlist the aid of a neighbor.
The easiest way is to start 'cold'; just watch the temp gauge and take some readings at easy points: 60, 80, 90, 100C. As you know, 90C is halfway in between the two lines that mark 80 and 100C on the temp gauge.
The most important are the readings at 80, 90 and 100C. They should be close to what the table says. If way off, then r&r the sensor (B11/2).
Do the same thing for B10/8 and watch for the readings around 100C. Remove the Cool Harness for this testing. BTW, you probably have to close the hood to try to get it to 100C.
If the SENSORS are ok, then you may need to test the car's electronics. Mercedes recommend the use a resistance substitution 'box' (rsb).
To test the AUX FANS operation: Remove the cable that connects to the B10/8 sensor and hook-up the rsb.
1) Set the resistance to 310 ohms. The fans should come on 1st stage (low).
2) Set the rsb to 250 ohms: fans should come 2nd stage.
3) Set rsb to 200 ohms; fans should be on high.
This testing can be done with discrete resistors: select/test to make sure that they MEASURE very close to the three values: 310, 250, 200 ohms. Just clip them across the B10/8 leads.
Then let us know what happens.
Regards . . . . JimF
'94 S500 Cpe
Visit my Mercedes Web Page