You may need to have your HVAC system inspected, this may be a blend door in the dash that is stuck, or the defrost air outlet may be clogged. Also, there is a defroster valve actuator that allows all these electronic functions, which may need to be inspected as well.
Hope this helps!!
〉 Answered on Feb 4th, 2013 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions