Cooling fan

[Exekiel69]

There is a cooling fan in front of the radiator that one day just went ON and does so every time the engine is running yet the engine does not overheat. Tried chasing the wires and they look to go right into a fuse box, any ideas why it is running all the time.

Thanks.

 

[cdude20]

On the grille side of the radiator? Usually that is an extra fan that goes on to help the A/C. On most cars I have seen, it is on all the time the A/C is on. Mercedes may be different but thats my 2 cents.

 

[The Warden]

Forgive my memory, but what year's the car?

cdude's correct that the electric fan on these cars is a part of the air conditioning system...there's one of two ways this fan is triggered. On older cars, there's a sensor in the a/c line that senses the temperature of the freon...if it sees that the freon's too hot, it'll trigger the fan on. On newer cars, the sensor senses line pressure instead of temperature and triggers the fan if the pressure's too high.

I want to say that the switchover year was between '85 and '86 (i.e. when the W123 chassis was replaced by the W124 chassis), but I can't say for certain.

IIRC the W124 chassis also set up the electrical so that the fan could be triggered on if the engine coolant temp got above a certain point, but I'm not certain since I haven't really dealt with the 124.

FWIW I saw the fan on my old '83 300D turn on on a very hot day even with the a/c system empty...my best guess is that the day simply got hot enough that, even with no freon in the system, the line got hot enough to trigger the fan.

Hope that helps some...good luck