740il Aux Fan not running on High - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 06-15-2013, 06:55 AM
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Cool 740il Aux Fan not running on High

Tried everything replaced electric fan, thermostat, fan sensor in radiator, fuses are good. low fan operates when a/c comes on, but not in the high speed mode.
As temp. rises a/c clutch kicks on and off, no high speed. Even with a/c off when temp. get high, fan should kick in and cool, but it does not.
What other problem could cause fan not to operate on high.
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#2 (permalink) Old 06-15-2013, 08:22 PM
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Does the auxiliary fan stay running on low speed when it should change over to high speed, or does it turn off totally?
Looking at another post it looks like there may be two resistor packs positioned behind the fan which limit the current flow (and speed) of the fan.
Replaced aux fan resistors on my 97 E39. Same repair kit for E38.
I am not sure if one of the resistor packs is used on the high speed mode, but it may be worth checking the resistor packs (and fan wiring) by disconnecting it (the fan) from the control circuit (connector behind front grill to the right side of the fan), and putting 12v directly onto each (in turn) of the pins (male). You will need a 12VDC supply and negative wire to do this, but if you're not sure about what's required you probably shouldn't be attempting this yourself.
Good luck and let us know how you go.


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#3 (permalink) Old 06-16-2013, 08:31 AM
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I have replace the fan with a new fan that has the new resistors attach, I can unplug the sensor that goes in to radiator that control the high and low speeds and ground the high speed to the brown wire in the pin and it works. The same with the low speed it works.
All fuses and relay are OK.
The fan will continue to run on low speed as long as the a/c is on, but will not go to high.
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