How can I fix the radiator cooling fan that is running on high speed all the time on my Mercedes Benz 2006 C230?

As soon as I start the car the fan comes up even when the car is cold, the temperature gauge is normal, the coolant level is where is supposed  to be. The car is running perfect, but the only thing is that the fan stays running on high while the car is on.


Thank you in advance 

Ill be waiting for you response.