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Pack Start-up
When you put the pack switch to AUTO, the flow control and shutoff valve opens. The valve opens at a rate that gives efficient air cycle machine acceleration. The air flow increases to 60 lb/min in 5 seconds, then increases to the schedule rate in 15 more seconds.
Normal Pack Shutdown On The Ground
When you put the pack switch to OFF, the flow control and shutoff valve closes. The valve closes at a rate that permits condensed water to evaporate from the pack.
The air flow decreases to 60 lb/min in 15 seconds, stays at 60 lb/ min for 15 seconds, then goes to 0 in 5 seconds. This sequence lets the pack temperature increase. Water condensation stops, and any water left in the pack evaporates.
Pack Shutdown In Flight Or Protective Pack Shutdown
If you put the pack switch OFF in flight, the flow control and shutoff valve closes slowly. The pack air flow decreases by 25 lb/min per second as the valve closes. The valve closes at this same rate for a protective pack shutdown from an overheat condition or a pack failure.
Stall Warning
The valve closes quickly for a stall warning condition. Air flow goes to 0 in less than 1/2 second
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AIR CONDITIONING -PACK FLOW CONTROL -FUNCTIONAL DESCRIPTION -START-UP AND SHUTDOWN

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AIR CONDITIONING -PACK FLOW CONTROL -FUNCTIONAL DESCRIPTION -ASCPC FLOW CONTROL

General
The ASCPC is a backup to the CTC for these functions:
*
Trim air system shutdown

*
Backup pack flow control

*
Pack shutdown.

The left ASCPC gives the above functions for the left CTC and the right ASCPC gives the above functions for the right CTC.
See the section on trim air pressure regulation and shutoff control for more information about the trim air system shutdown function provided by the ASCPC (SECTION 21-62).
Backup Pack Flow Control
The CTC gives a CTC status signal to the ASCPC. If the CTC fails or has no electrical power, the status signal is not valid. The ASCPC gives backup flow control if it has valid data from the pack outlet temperature sensor and the compressor discharge temperature sensor. If the temperature data is not valid, the ASCPC will not give backup pack flow control. The upper flow control valve closes and the lower valve goes full open, this is the default position for the valve when air is available in the pneumatic system.
If the sensors give valid data the ASCPC gives backup flow control. The upper flow control valve closes and the lower valve controls air flow into the pack.
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The ASCPC keeps the flow rate at 67 pounds per minute if the conditions for flow schedule 4 are active. See the page Pack Flow Control -Functional Description -ASCPC Flow Schedules in this section for more information about the conditions that make flow schedule 4 active.
If flow schedule 4 is not active, the ASCPC keeps pack outlet temperature between 40F (4C) and 110F (43C). To do this it keeps the pack flow between 150 pounds per minute and 250 pounds per minute. The ASCPC keeps the pack flow at 150 pounds per minute as long as the pack outlet temperature is more than 40F (4C) and less than 110F (43C). If the pack outlet temperature is low, the ASCPC increases the flow to 200 pounds per minute. After 30 seconds, if the temperature is still low, the ASCPC increases the flow to 250 pounds per minute.
If the pack outlet temperature becomes more than 110F (43C), the ASCPC decreases the flow rate in the same way. The minimum flow rate is 150 pounds per minute when schedule 4 is not active.
Pack Shutdown
The ASCPC closes both flow control and shutoff valves for any of these conditions:
*
Pack outlet overheat with CTC status invalid

*
Compressor discharge overheat

*
Pack switch OFF

*
Stall warning.

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AIR CONDITIONING -PACK FLOW CONTROL -FUNCTIONAL DESCRIPTION -ASCPC FLOW CONTROL

For all conditions except the first, the ASCPC pack shutdown function is a backup to the CTC shutdown function.
The overheat shutdown function resets when you put the pack switch OFF then ON if the overheat condition no longer exists.
When the ASCPC commands the upper and lower flow control valves to close, it also give a signal to AIMS and to OPAS for these pack off indications:
*
OFF light in the left pack switch

*
PACK L advisory message.

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