One major thing that can happen is that no matter what setting, it won't blow out your dash vents. Just the windshield vents. It defaults that way so you can have defrost available if there is an issue with it.
2011 Ford Fusion SEL 3.0L DOHC V6
2005 Mercury Sable LS 3.0L DOHC V6 (The Beater)
2005 Ford Taurus SE 3.0L FFV OHV V6 (Sold)
2006 Ford Taurus SE 3.0L OHV V6 (Sold)
2005 Ford Taurus SEL 3.0L FFV OHV V6 (Sold)
2007 Ford Taurus SE 3.0L OHV V6 (Sold)
1999 Ford Taurus SE 3.0L OHV V6 (Sold)