Baezax6

Hey guys I'm new to the Lincoln world I just got a 2001 Lincoln Navigator And I'm have problems with the vents When I put it to max ac it starts blowing out the windshield defrost and I Can go back to vent and swaps but it will go the floor vents either I figure that if it would operate the front vents to defrost I don't have a vacuum leak I'm at a stand still any help would be appreciated