49-11-00
 ALL  ú ú 01 Page 5 ú Nov 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES/MAINTENANCE MANUAL ////////////////////////
E.  If the APU engine speed does not get to 50%, the APU engine will not start. The 90-second time delay will stay energized for the 90 seconds. After the 90 seconds have gone by, the 90-second time delay completes the circuit to the APU control unit. Electrical power is removed from the start relay R5, ignition unit, 90-second time delay and the fuel solenoid valve. The starter motor and ignition unit stop operation. Also, the fuel flow to the combustion chamber stops.
 F.  The APU master switch is moved to the OFF position to stop the APU operation. Electrical power is supplied to the overspeed oscillator in the electronic speed switch. This will send a signal the same as an engine overspeed. The 110% contact in the electronic speed switch opens and removes the electrical power from the fuel solenoid valve. Electrical power is removed from the APU control unit to fully isolate the fuel solenoid valve. When the fuel solenoid valve closes, the fuel flow to the combustion chamber stops. The APU engine slows down and stops. While the 110% contact in the electronic speed switch opens, electrical power is supplied to close the APU fuel valve. When the APU fuel valve is fully closed, the inlet door actuator closes the air inlet door. If there is a problem with the APU control unit, the OVER SPEED light on the P5 forward overhead panel will come on.
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APU POWER PLANT - MAINTENANCE PRACTICES
_______________________________________
 1. General
_______
 A.  This section contains these tasks:
 Procedure_________ Paragraph
 APU Start and Operation ................................... 2
 APU Usual Shutdown ........................................ 3
 APU Fire Shutdown ......................................... 4
 APU Automatic Shutdown .................................... 5
 Dry Motor the APU ......................................... 6
 Wet Motor the APU ......................................... 7
 APU System Deactivation (The APU Installed) ............... 8
 APU System Activation (The APU Installed) ................. 9
 APU System Deactivation (The APU Removed) ................ 10
 APU System Activation (The APU Removed) .................. 11
 APU Preservation (Less than 180 Days)......................12
 APU Preservation (180 to 365 Days).........................13
 APU Depreservation ....................................... 14
 Control Air Leak Check ................................... 15
 APU Inspection After Overtemperature During Start ........ 16

 TASK 49-11-00-862-052
 2. APU Start and Operation
_______________________
 A. General
 (1)  The APU start and operation has the steps to start the APU and monitor the APU operation.
 (2)  Figure 201 gives the recommended operation limits for the APU engine. When an overtemperature condition occurs, you must stop the engine. Do not restart the engine until you correct the cause of the overtemperature.
 (3)  You can find high temperatures as far as 30 feet (in some wind conditions) from the APU exhaust duct. When the APU is started, fuel can ignite if it is in the tailpipe. This cause long flames to blow out of the APU exhaust duct. You must not try to start the APU in the range of flammable material or fumes.
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 49-11-00
 ALL  ú ú 01 Page 201 ú Nov 15/95
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////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
　
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