My aux fan works when I give it direct 12v, but it never goes on by itself... which makes my AC semi-cold when i'm not moving.

What is the gross wiring schematic/what could be wrong ?

I thought it could maybe be the thermo switch

 

I can get you that diagram but I'm gonna need you to PM me your email. The file size constraints on here are absolutely ridiculous.

 

My issue was a fuse, orange 40 amp, that I needed to change and my aux fan worked then. The shop I called said there was no fuse, they wanted $500 to replace the fan.

 

My issue was a fuse, orange 40 amp, that I needed to change and my aux fan worked then. The shop I called said there was no fuse, they wanted $500 to replace the fan.
On my A6 the fuse was located behind a panel beneath the steering wheel , remove two bolts, drop the panel.