I have 2001 X5, and I am having the same question regard to the aux fan that is sitting in front of radiator, does this fan for A/C or radiator? I notice the main fan inside engine area works fine every time I turn on engine except the aux fan outside. It looks like it does not cycle even though I turn on AC but my AC works fine, it is cool as normal. My temp is still at the middle even I turn on AC all day but I smell kind of burning coolent. By the way, I just had my radiator replaced because it broke. Does anyone have any idea about the aux fan, does it suppose to cycle all the time or cycle whenever it is hot. Please advise.