1998 Mustang GT A/C / Blower problems

GA_googleFillSlot("Forums_ROS_300x250_noad");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.