Here's some info on how the AUC (auto recirculation) system works.
When NO LEDs on the AUC button is illuminated...the fresh air flaps are OPEN
Press the AUC button once (left LED illuminates)...you're in "A" (auto) mode...the flaps fresh air flaps and recirculation flaps close/open on a schedule based on data from the AUC sensor in the engine bay. So you won't necessarily "hear" anything like a change in the sound of the blower just because you pressed the button once.
If you want to specifically close the fresh air flaps (and probably hear a change in the blower)...you press the AUC button twice so that the LED on the RIGHT side of the re-circulation button is illuminated: