1998 Mustang GT A/C / Blower problems

Ok so my fan is only blowing out the defrost and floor vents, for all a/c, heat, and vent.. It has done this since I bought it, it didn't just suddenly occur.. I was wondering if this has happened to anybody else, and what did you do to fix it, or just any suggestions...
Would replacing the control unit help?.. I'm not sure of that cause I had a sunfire that had a similar problem and replacing it did not help, so just any suggestions would be helpful, Thanks.

You could have one of the blower doors jammed not allowing it to flow the air up. Either way A/c is a pain in the butt for a do it yourselfer. Best to take it to a shop or someone experienced. Replacing the control unit wouldn't help.

I had the same problem in my 1997 ford E350 van, you probably have a vacuum leak somewhere. When there is no vacuum do to a leak or other problems the air is directed to the defrost door by default. There are vacuum actuated motors that control the flow of air to diffirent vents and if they dont get vacuum they just go to defrost so find the vacuum leak and replace the hose and that will fix your problem.