Remove it and connect the black and red wires that go to the fan controller across the battery, red to + and black to -
If it runs, get a new fan controller module : A C Fan Blower Motor Resistor RU567 Fits Mercedes SLK320 SLK350 AMG 2108206210 | eBay
If not, then get a new fan : http://www.ebay.com/itm/HVAC-Blower-Motor-4-Seasons-75897-/281409031445?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3ACrossfire&hash=item4185490d15&vxp=mtr