The fan will not go on until you hit 115 -- it will then run until the temp drops down to 105. If it stays at 110 on the hightway in very hot weather MB says this is design intent.
To get the low speed they have a resistor - in my car it is right up front in the airstream -white - it looks like the resistor for the ignition. You can bypass this and then bypass the pressure switch (red on my car) this will check both of the components the fan will then run on high.
I did not have to look into the rest of the controls for the fans - I was surprised that the fans did not come on with the as on low as other cars do in fact as many other MBs do - But then I have never had any problems - and I may not now if it is just low gas charge. But I would think that a simple relay of the compressor to switch on the low side of the fan would increase the cooloing capacity