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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
ABC
.15^ .01^ .15^ .01^ D
V56 BLEED AIR
(LOAD CONTROL)
VALVE E
S284
FULL OPEN
SPOOLFOPEN
DOOR
.05^ .05^ G
SWITCHNOT FULL OPEN
DIFFERENTIALS
AIR PRESSURE
R204 APU EGTREGULATOR
RESISTOR
OPEN
+V
M299

H
M
M
INLET
DOOR

M278 MISCELLANEOUS
I
CLOSE ACTUATOR
SWITCHING MODULE
OPEN
V43 APU FUEL

R216 APU
CLOSED HARNESS
SHUTOFF VALVE
(AFT SPAR-BALANCING
LEFT WING) T2J
RESISTOR
SURGE
COMPRESSOR
HOURMETER  BLEED
2
1
INLETVALVE
TEMPERATURE
SENSOR CR AL
ELECTRONIC
TEMPERATURE C
CONTROL

HIGH OIL
SEQUENCINGAFT CARGO
TEMPERATURE
OIL PRESSURECOMPARTMENT
SWITCH
SWITCHEXHAUST
KB
LOW OIL
OVERSPEED
SHT 1 A
PRESSURE TACHOMETER
OSCILLATOR
LOW OILL
SWITCH
FUEL QUANTITY SOLENOID SWITCH
GENERATOR
IGNITION SHT 1 D
50%
VALVE M
-
APU CONTROL
+
110% N
THERMOSTAT
B 2
C MOTOR
STARTER
S 95% REMOTE FIRE
O
FUEL
SHUTDOWN PANELS634 ELECTRONIC SPEED SWITCH
CONTROL
PROPORTIONALUNIT
CONTROL VALVEP
1 S
E3
RACK
FORWARD
OVERHEAD
Q
PANEL, P5THERMOSTATSELECTOR
R
SOLENOID
APU FUELNOTE: REFER TO WIRING DIAGRAM MANUAL FOR WIRING DETAIL
SHUTOFF APU CONTROLVALVE 1
AIRPLANES WITH THE ELECTRONIC TEMPERATURE CONTROL START
UNIT, M280RELAY, R5
2
AIRPLANES WITHOUT THE ELECTRONIC TEMPERATURE CONTROL
MAIN EQUIPMENTBATTERY CENTER ACCESS DOOR
APU Control Circuit SchematicFigure 2 (Sheet 2)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
B.  With the BAT switch on the P5 forward overhead panel in the ON position, the APU master switch is moved through the ON position to the START position. When the APU master switch is released, the APU master switch will stay in the ON position. The APU control unit holds the start signal from the APU master switch and the start relay R5 does not energize until the air inlet door is fully open. The circuits for the HIGH OIL TEMP or FAULT light and the LOW OIL QUANTITY or MAINT light are armed. The LOW OIL PRESSURE light comes on. The automatic shutdown for a high oil temperature becomes serviceable. The APU fuel valve opens. After the APU fuel valve opens, the power goes to the inlet door actuator. The inlet door actuator opens the air inlet door.
 NOTE: If the APU master switch is not set to the START position before
____ the air inlet door fully opens, the APU control unit will not permit the APU to start.
 C.  When the switch for the air inlet door is in the FULLY OPEN position, power is supplied to the sequencing switch for the oil pressure. Power also goes to the 90-second time delay in the APU control unit. The start relay R5 closes and sends a signal to the APU control unit. This completes the circuit to the starter motor. The starter motor starts to turn the APU engine.
 D.  As the APU engine turns, the oil pressure increases. When the oil pressure increases to approximately 4.0 psig (27.6 kPa), the sequencing switch for the oil pressure closes. This completes the circuit to the fuel solenoid valve and to the ignition unit. The fuel solenoid valve opens to permit the fuel flow to the combustion chamber. The ignition unit causes the igniter plug to make sparks. The APU engine has combustion and starts to increase its speed. When the APU engine speed gets to approximately 19,000 to 21,000 rpm, the 50% contact in the electronic speed switch opens. This removes the electrical power from the 90-second time delay and the start relay R5. The starter motor disengages, slows down and stops. When the oil pressure gets to 55 psig (379 kPa), the low-oil pressure switch opens and the LOW OIL PRESSURE light goes off. The APU engine continues to increase its speed. When the APU engine speed gets to approximately 37,300 to 38,900 rpm, the 95% contact in the electronic speed switch is energized. This removes the electrical power from the ignition unit and sends a signal to the solenoid for the bleed air valve. Also, the 3-way solenoid valve is energized and the APU GEN OFF BUS light comes on. With an APU engine speed of 95%, the automatic shutdown circuit for a low oil pressure can operate.
　
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