BenzWorld Junior Member
Date registered: Apr 2012
Vehicle: 1990 300SL
Location: Colorado USA
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
You can easily bypass this sensor
I have the same issue on my 300SL. When I killed my entire cooling system with the wrong antifreeze, I found that my fans were not engaging either. I went through a lot of searching to find what I thought was the correct sensor/switch and am still unsure I got the right one. My Merc spec says it may not be the sensor at all but could be anything along that wiring, even with the working bypass.
It's easy enough to bypass the sensor as I did so that fans stay on whenever the key is on but that's not really very good for the fans to be on all the time. I did discover that without the bypass, the fans work properly as long as the cooling/heating is on. So you can set the temp and just leave it on Automatic setting all the time and it should kick the fans on and off. (The A/C will not work if the sensor is bypassed) Just unplug the wires from the sensor and connect the bypass (a wire with an alligator clip at each end) to each of the wires and it will cause the fans to work with the key. You can wire the bypass to a kill switch inside the car if you want, but for me it's not worth it. I'll just leave the climate control on auto.