The Aux button can be used to mimic the air-conditioner's settings in the rear to those in the front. It is done by cycing the Aux button off and on. It is pretty handy and comfortable to use if you don't have any back seat passengers.
I use the aux all the time to cool the cabin from the rear instead of blowing cold air in the face. My only problem is it appears you have to change the blower speed from the second row console and not the main front console.