Theory Of Operation
WARNING: This page is about a different car, the 2013 RAM 1500. However, it is still accessible from the selected car via links, so may be relevant.
The Air Suspension Control Module (ASCM) detects that it cannot increase reservoir pressure (fill) when the system is operating. In order to fill the reservoir air must be go through the intake air hose, ambience valve, reversing valves, the compressor, and finally through the air line leading to the reservoir itself.