The 2.3 has an electromagnectic fan not a clutch. It kicks in at 105C give or take depending on year. If its cool enough outside and your radiator is old it will just hover in heavy traffic near the 100C mark and never trigger the fan...annoying as hell.
I think your dealer is wrong the mini electric fan should not come on before the big electromagnectic fan. The mini fan kicks in at a 5 degree higher temp and complements the big fan or when the AC is on.
The fan switch for the electromagnectic is screwed into the top of the the engine behind the oil cap. If you are going to order a new one make sure you give your vin number so you get the right one.
Here are some threads that discuss this:
92 190E 2.6 Overheating Problems
Aux. Fan advice requested.
cooling system wiring
[Edited by yal on 04-12-2001 at 01:50 PM]