Go check fuse #7,#D and check auxiliary fan
relay K10 low speed,K9 high speed,locate inside fuse box under hood ,also check
auxiliary fan preresistor locate behind driver side headlmp unit,coolant temp sensor
locate on top of cylinder head,auxiliary fan
switch is locate on deire (red) and possible
bad auxiliary fan motor(try to turn by hand)
hope this help.

------------------
MB STARS Master Guild Technician,12 years MB tech
5 years independent shop owner