Aux Fan's

[dsimguy]

Greetings' My 300E is overheating with the A/C on, the aux fans do come on but just momentarily. the book talks about the fans running at two different speeds and I believe I have located the large resistor just aft of the left head light assy, and it's glowing red hot. Doesn't look normal. Anybody know what might cause this?

[Robert Goodwin]

A short circuit will cause any resistor to glow red, even if for only a moment as it burns in two.

Unless I am mistaken, one of the fans (you do have 2 seperate electric fans in front of the radiator, right?) is controlled by the A/C system temp sensor on the reciever/drier.

The other fan is controlled by a heat sensor switch on the engine and usually comes on when the temp gauge is at or near redline.

If you have a single electric fan, the low speed is a function of A/C system temp and the high speed (unmistakable sound of an airplane taking off) is controlled by the engine temp sensor.

The 2 speeds are changed by inserting a wirewound resistor in line with the fan. High speed, resistor shorted out, low speed resistor in circuit.