Alpha Technologies APU Control Module (ACM) - Manual (Page 10)

018-340-B0-001 Rev. A 10
1.0 System Overview, continued
1.2 Theory of Operation, continued
1.2.4 Normal APU Shutdown
The ACM will initiate a normal APU shutdown when AC line is qualifi ed, DC bus
alarm is not active, the 12 minute cool-down period has elapsed, and the Engine
Run command is not active. Otherwise, the ACM will continue to run the APU until
the above conditions are met or a major alarm occurs. Also, the APU will run for a
minimum of 30 minutes if started due to low DC Bus voltage, or if the RAS switch is
switched from Run to Auto (See section 3.1, Indicators, Controls and Connectors).
1.2.5 Abnormal APU Shutdown
The ACM will immediately shutdown the APU under the following conditions:
• Major alarm
• Activation of manual engine stop switch
• Receipt of software engine stop command
• General generator failure