Air Selection Knob Stuck

I have a 2012 Impreza with manual climate controls. For whatever reason, the air selector knob (all the way on the left that directs the flow of air) will not turn all the way back counterclockwise position. The selector will sit between the first (Dashboard) and second (Dashboard and floor combo), and not move any further back. What do I need to check before I think about replacing the controls themselves?