I love my 2014 express 2500. My front air is working good. But my rear air in the ceiling vents don't blow any air at all. I have air coming from side wall vents but it could be cooler. Is the ceiling switch gone bad?? Is it a complicated fix?? HELP...

 

the rear hvac case located near the r/r quarter trim panel uses an electrically operated motor to move a mode door. the mode door is the part that moves to change airflow from the floor to roof. a good scan tool can monitor the door commanded and actual positions....working properly...they should match.