Chevrolet Repair: chevy ac trouble, chevy silverado, floor vents

Question
I own a 2003 chevy silverado, I switched ac airflow from dash vent to floor vent, and now am unable to switch back.  The fan out put seems to be stuck on the floor vents. What part should I be looking to replace after removing the dash?

Answer
Look for a vacuum or electric operated vent door actuator.  Will be an arm there you may be able to move with pliers.  This door may be stuck, or your vacuum supply to it may have stopped.  It should be vacuum apply and spring return.  Look to see if spring is bad.