The aux fan is an output for the DME.

The compressor on/off wire going to the IHKR from the DME might be something to look at. Some more reading about how it works (is there anything bus controlled on the IHKR??) and knowing what modules are being read and activated would help.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)