Actually you have three fans...the main fan behind the shroud and two auxiliary fans.
The main fan is on a clutch, and when engaged, it does spin in proportion to the engine speed.
The auxiliary fans get a signal from the temperature sensor to indicate that additional cooling is needed, and they spin a either a fixed low or high speed, depending on cooling demands.
Actually the W124 cooling system process is a bit complex, with all sorts of backup plans to handle overheating issues. One such plan is that the A/C compressor gets shut down under dire circumstances.
If the weather is mild (not hot) right now, you should be okay.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car