Hello,
I just picked up a 2004 A6 2.7T 6spd, and was playing with the front air controls to try and pass air through the back vents, but I wasn't having any luck. I dont know if there is a seperate fan for the back vents, if it is only for heat, A/C or both...but I can't figure out how to get any airflow out the rear vent. Any help would be greatly appreciated!!

 

There is only one fan blower, if your not getting any air out of the back vents you either have a problem with an air flap motor (you should have a fault for this) or someone had the front seats out and was doing work to the center console and forgot to re-connect the air ducts to the rear of the car.