Thanks guys for the grt info. Unfortunatly I couldn't find the relay (i have no clue on its location). So what I did unplugged the sensor cable (mine is a 3 wire sensor, so as the guy in the video say, I didn't dare to short it). The turned the a/c on. The Aux fan started and ran indefinitly and stopped as soon as i connected the sensor connector back. So i guess it is safe to assume that the fan is good. Now my task is to find the relay and try and short it as in the video.
Anyone know where the relay is located for a BMW X5 E53? Unfortunatly the video is for a Chevy. So the setup is totally different.