Have you checked your owners manuals for information on how the leveling system operates. On mine when you initiate the leveling process, the air bags dump pressure to lower the coach before the leveling jacks activate and complete the leveling process. Deflating the air bags insures the jacks do not have to extend any more than necessary and helps compensate for an unlevel parking site. The air bags on my coach will not reinflate while the jacks are extended, yours are probably the same. The engine driven air compressor should operate as RV Roamer said but not inflate the air bags while the jacks are extended.
'07 Winnebago Journey 34H, ISB-02, MH2500
Toad - '08 Ford Taurus X
Blue Ox, Aventa
US Gear UBS