An auxiliary power unit (APU) compartment air inlet system seals, via one or more inlet doors driven by a single actuator, an APU compartment, and isolates the APU inlet and cooling system inlets from each other. The system includes either one or two inlet doors, depending on the number of ram air inlets formed in the APU compartment. In either instance, however, a single actuator is used to move the inlet door(s) between open and closed positions.