Re: Aux. Fan (Low Speed) help (archive)

The low speed circuit is shunted thru a ballast resistor which is mounted on the edge of the fan at about the 4 o'clock position. You can access it thru the kidney grills which come off easily by removing the two clips on top. Follow the leads down to a 3-pin socket down below the bumper. Unplug the socket & measure the resistance across the blue & black wires. It should read in the neighborhood of .5 ohms. The resistor is .5 ohms x 85 watts. You can use four 2 ohm x 25 watt ceramic resistors in parallel to get .5 ohms x 100 watts & save the $34.75 the dealer gets for a new resistor. My old "fried" resistor measured 2.5 k-ohms (basically open) & works fine now with the new resistors. The fan should run continuously on low when the a/c is on & ignition on whether engine is running or not.

If the resistor is ok then check the relay which is in the separate small relay box in front of the left shock tower, ref.:

http://www.nmia.com/~dgnrg/relay1.jpg

http://www.nmia.com/~dgnrg/relay2.jpg

gale
92 735i

Low speed not operating, hi speed ok. Fuses OK! I jumped radiator temperature switch hi speed came on (black/grey to brown). Jumped low speed (violet/grey to brown) low speed wouldn't come on. I could hear relay click but fan did not operate. How do I check further?

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