A system and method for supplying compressed air from an auxiliary power unit to a main engine starter motor. The inlet guide vanes are controlled using either first or second inlet guide vane control logic and the surge control valve is controlled using either first or second surge control valve control logic. When the first inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand signal, when the second inlet guide vane control logic is used, the inlet guide vanes are positioned based on a demand schedule, when the first surge control valve logic is used, the surge control valve can be commanded to repeatedly move to only a fully-closed position and a fully-open position, and when the second surge control valve logic is used, the surge control valve can be commanded to the fully-closed position only when maximum flow is commanded.