Fan was not working so, I bought a new fan, installed it and still no go, IT WILL NOT TURN when engine is started on. Fuse is good. There is power and ground going straight through to the wires (red and brown) and right to the connector pins on the harness. I checked them with a test light...I even let it warm past 80* degrees to 90 and still NO GO...I don't no if it is normal for the fan not to turn at all from 0-90* degrees. I think on this engine normal operating temp is 80*...What else can it be? This is crazy? I do have a code that indicates I have low refrigerant and I know I have a leak some where that the AC is not working, there is little to no refrigerant pressure in the AC system, but the fan should come on without AC...What the heck!

 

Any faults in engine ecu?
there are 4 wire to that fan. Thick power and ground. And 2 thin wires they must have 12v with ign on and the other I think is green blue will have a lower voltage. First make sure that ign supply is good! Also by about 95 to 100 deg the fan should be turning

 

Ok, so i let it warm up to 95* degrees Celsius and sure enough it came on at first speed (1st), which is good, but is that normal? I always thought they came on when you turn the engine on at 0* degrees and then when it hit 95-110* degrees Celsius (200-230 Fahrenheit) it goes to a faster speed (2nd) to bring it down to 80* Celsius. Maybe I'm wrong with Mercedes...I have an old 1977 Chevy and the fan comes on as soon as you start the engine and always stays on...

 

Its all about saving energy. Why run a fan when it's not needed. It will run faster if it cannot control the temperature from 95 degrees. Also when your AC works it will also run to keep the condenser cooled