I have a 95 525 ia and I had a couple of questions for you e34 aficianados out there (you know who you are....). I am stumped on this topic

1) When should the aux fan come on?
2) How can you check if you have power going to it?
3) How can I test to see if the aux fan is working properly?

I have my AC, and it is working fine, and the temp guage is always at 12, but there are times when I am at a stop, it feels like the aux fan is kicking in but I do not think that it is. The fan is 1 yr old. Fuses are all ok. What can I do to test if it is working correctly. Any advice would be appreciated.

Brian