Mercedes: merc 190e 2.3L, ac condenser, fan clutch

Question
Robert, can you explain how the fan clutch works; i.e pnematic or electric? When the car is in the run mode, the fan blade spins but not to the speed of the pulley behind it. I am trying to figure out how to troubleshoot it. Thanks

Answer
Mark,
If the fan in mounted between the engine block and radiator and  has a belt drive pully, it probably uses a fluid coupler between the pulley and blades.
The fluid clutch has a bi-metal coil that actuates an internal valve and closes to allow the fluid to move inside the clutch. As the temperature rises that clutch is engaged to move the blades in sink with the pulley.
This pulls more air through the radiator to improve the cooling.
When the temperature is cool enough then the bimetal strip move the valve and allows the blades to slip. The slippage improves engine economy because does not put so much drag on the engine when airflow is good as when you are out at road speed.
If the fan is electric, it has thermostat switches that engage the fan when the radiator needs more airflow as in traffic, and the fan(s) are switched on full time when the AC is operating to help remove the additional heat generated by the AC condenser. The electric fans will sometime continue to operate after the vehicle is shut down to help remove the excess heat from the radiator to help keep it from boiling over.

Hope this explanation is OK. If you have additional questions, feel free to ask.
Good Luck
Rob