In other words , don't expect to see that fan until the a/c system sees a High Thermal Load ..ie, high Ambient temp condition..
In New England and cooler climates , it is possible to see a perfectly running a/c system that never gets a high side pressure command for aux fan b/c the condenser is not exposed to a High Thermal Load one would see in southern climates ....
Aux fan ONLY comes on when the A/c system is being taxed and the high side pressures are reaching exterme/dangerous pressures...and when this condition is met, the pigtail sw it closed, activating the aux fan...the added fans airflow across the condenser keeps the high pressure in Check..
That is the AUX LOW FANS SOLE purpose.

Once again, gauges will tell the tale if these pressure are not being attained for sw cut-in activation..........

Baically, you should see a low fan when A/C is ON full blast, the car is at stand-still and idle, and it is a HOT/HUMID day ..and even then they will cycle On/OFF according to conditions/pressures..
I think much of the confusion is b/c many car just have the fan wired to come On anytime the compressir comes On, but that is not the case with your chassis system. Benz design mandates aux airflow only when required.
Same goes for the HIGH fan circuit.. one constantly sees post here that claim they never see the high fan when the coolant temp is rising...well, they don't see high fan b/c it is sensed to NOT come ON until coolant temps are in excess of 107C..a rare occurance...
** Many of us do not like that spec and use a resistor modification to that sensor to drop that to a littte lower cut-in temp.**

__________________
A Dalton