Worked on the E28 this weekend (after Svending) to try and get the aux fan working. It is supposed to come on any time the AC is on, and I think when the engine is over a certain temperature. A few weeks ago I verified that the fan was in fact functional by removing it and connecting it directly to the battery.
Until this weekend I didn’t have more time to figure it out. Following the wires from the they go to this connector.
Turning on the AC didn’t net any change in the readings on any of the three wires. So off the mye28.com for some additional research. I’m still not 100% sure how they all interact, but there is a low and high temp switch on the side of the radiator in addition to the AC switch on the dash. If you jump the two terminals of the low temp one together the fan turns on low regardless of the AC switch position. Similar with the high temp switch except the fan turns on high speed.
Seeing as I live in Houston and it is close enough to summer I took the easy road for today and jumped the low temp switch so the fan runs all the time.
At this point I assume there is a fault with the AC switch on the dash, or somewhere in between. I just didn’t have any more time today between kids yelling at each other and helping my dad with stuff at his house to further diagnose or even read.
Google Photos enhanced picture for your time.