(2)
At 7% speed, the fuel solenoid valve opens, the ignition unit energizes and the EGT increases from the ambient temperature.
(3)
At 50% speed, power is removed from the start relay R5. The dc voltmeter shows approximately 24-28 volts. This shows that the starter has disengaged.
(4)
At 95% speed, the APU GEN OFF BUS light comes on to show that the APU bleed valve is ready for pneumatic loads. The APU electrical generator system is ready. Power is removed from the ignition unit and the time totalizer meter is energized.
F. APU GEN OFF BUS Light (Blue)
(1) This light comes on when the APU engine speed is greater than 95%. At 95% speed, the APU engine can be pneumatically or electrically loaded.
G. APU BLEED Switch
(1) When the APU engine speed is greater than 95%, this switch operates the bleed air valve.
H. FREQ Meter
(1) This meter will show the frequency of the APU electrical generator when the AC selector switch is set to APU GEN. You can use the FREQ meter to find the APU speed. The FREQ meter will show 405-410 CPS when the APU engine speed is 101.3-102.5%.
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I. EGT Indicator
(1) This indicator shows the exhaust gas temperature (EGT) of the APU.
J. Duct Pressure Indicator
(1)
During the APU operation, with the APU BLEED switch in the ON position, no electrical load and no bleed air flow, the bleed duct pressure at sea level should be 45 |5 psig (310 |34 kPa).
(2)
If the bleed air pressure is not within the operation limits, refer to the air pressure tables with the measured ambient temperature and barometric pressure (AMM 49-11-00/201).
K. LOW OIL PRESSURE Light (Amber)
(1)
For satisfactory APU operations, this light will come on when the APU master switch is put in the ON position. When the oil pressure is greater than 55 psig (379 kPa), the light will go off.
(2)
If the oil pressure decreases to 45 |3 psig (310 |21 kPa), the light will come on. In 10 |2 seconds, there will be an automatic shutdown and the MASTER CAUTION light and APU annunciator will come on.
L. LOW OIL QUANTITY or MAINT Light (Blue)
(1) This light comes on when the APU oil quantity is less than
1.5 |0.5 quarts.
M. HIGH OIL TEMP or FAULT Light (Amber)
(1) This light comes on when the APU oil temperature is greater than 275°F (135°C). Also, the MASTER CAUTION light and APU annunciator will illuminate.
N. OVER SPEED Light (Amber)
(1)
This light comes on for the following conditions:
(a)
The APU is stopped for an APU usual shutdown and there is a malfunction.
(b)
The APU has an automatic shutdown for an overspeed during the APU operation. This can occur in flight or on the ground.
(2)
It is necessary to find the cause of the OVERSPEED light. This will help to do the correct maintenance and to prevent damage to the APU.
(3)
AIRPLANES WITH -31 THRU -49 APU CONTROL UNIT; If the OVER SPEED light comes on when the APU master switch is moved to the OFF position after an unsatisfactory APU start, it is not necessary to push the OVERSPEED RESET switch before you try another APU start. The OVER SPEED light will go off during the next APU start.
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////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES/MAINTENANCE MANUAL ////////////////////////
(4)
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