Easy question for some

Bought my 3rd stang. It is an 04 Gt, BUT, a problem developed that I can't explain that is probably an easy fix:

When I set my blower on the A/C or heater to blow in the floor, it blows out of the defroster vents. Every other setting wks fine. But, the defroster setting and the floor setting do exactly the same thing!!

Any ideas???

thanks!!

Sounds like a vacuum line is disconnected somewhere.

take it to the dealer..new car warrentee?