D. Procedure
S 286-021
(1) Do the items that follow to do the condition check of the APU (Fig. 602):
(a)
Item 1. WRITE DOWN THE OUTER AIR TEMPERATURE
1) This will be used to compare the EGT no-load data for a heat exchanger test and a check of the acceleration time during an APU start.
(b)
Item 2. EXAMINE THE BATTERY VOLTAGE (MUST BE A MINIMUM OF 22 VOLTS) 1) Low batteries can cause the APU to start slowly or to not start.
2) The battery voltage can decrease to 16-20 volts when the starter motor engages, then go back to the initial voltage. If the voltage does not decrease, a weak clutch or terminals with corrosion can be the cause.
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A/C__________________ APU S/N______________ DATE_____________ APU SYSTEM MONITOR CHECK
WRITE DOWN THE DUCT PRESSURE (30-50 PSIG) (405-410 CPS) WRITE DOWN THE NO-LOAD GENERATOR FREQUENCY 17 SET THE ELECTRICAL LOAD TO 100 AMPS 16 15 14 ---WITH THE ISOLATION VALVE OPEN WITH THE PACK VALVES CLOSED WRITE DOWN THE APU EGT CLOSE THE APU BLEED VALVE OPEN THE TWO PACK VALVES AND SET MANUAL FULL COLD OPEN THE APU BLEED VALVE WRITE DOWN THE OPENING RATE OF THE APU BLEED VALVE OPEN THE APU BLEED VALVE AND THE ISOLATION VALVE7 8 9 10 11 12 13 (12-14 SECONDS) WRITE DOWN THE MAXIMUM EGT WHEN IT HAS BECOME STABLE WRITE DOWN THE GENERATOR FREQUENCY (396-404 CPS) WRITE DOWN THE DUCT PRESSURE (5-20 PSIG) 18 WRITE DOWN THE APU EGT -19 20 REMOVE THE ELECTRICAL LOAD FROM THE APU DO THE APU USUAL SHUTDOWN -_ 22 VOLTS) EXAMINE THE BATTERY VOLTAGE (MUST BE A MINIMUM OF 3 -4 MAIN ENGINE BLEED VALVES ARE CLOSED, AND THE ISOLATION VALVE IS CLOSED 5 START THE APU - DO A CHECK OF THE ACCELERATION TIME (SECONDS) WRITE DOWN THE NO-LOAD IDLE EGT 6 MAKE SURE THE PACK VALVES ARE OFF, THE APU AND THE ITEM 1 2 OPERATION/OBSERVATION DATA INSP WRITE DOWN THE OUTER AIR TEMPERATURE
APU Condition Monitoring Check
Figure 602
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////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES/MAINTENANCE MANUAL ////////////////////////
(c)
Item 3. MAKE SURE THE PACK VALVES ARE OFF, THE APU AND THE MAIN ENGINE BLEED VALVES ARE CLOSED, AND THE ISOLATION VALVE IS CLOSED
1) No steps are necessary.
(d)
Item 4. START THE APU - EXAMINE THE ACCELERATION - WRITE DOWN THE TIME FROM WHEN THE STARTER ENGAGES (AS NOTED BY THE DECREASE IN DC VOLTAGE) TO THE TIME THE APU GENERATOR "OFF" BUS LIGHT GOES ON (20-40 SECONDS FOR AIRPLANES WITHOUT THE ETC; 40-80 SECONDS FOR AIRPLANES WITH THE ETC)
1) This is to examine the condition of the battery circuit, the starter motor and the clutch, the fuel control, the electronic speed switch, and the EGT control system. A slow acceleration time can be caused by these items: a) Airplane battery - low voltage b) Bad APU starter cables c) A weak or bad starter d) Leakage from the diaphragm in the limiter for the fuel
control accelerator e) Leakage from the limiter valve on the fuel control accelaerator f) The crack pressure for the limiter on the fuel control accelerator is set to low g) The pneumatic control lines for the limiter on the fuel control accelerator are loose or have leakage
h) The air supply for the limiter on the fuel control accelerator is limited (the orifice is clogged or the line has ice in it)
i) Leakage from the 3-way valve solenoid j) AIRPLANES WITHOUT THE ETC; The APU control thermostat is set too low or stuck open
k) AIRPLANES WITH THE ETC; The proportional control valve does not function correctly.
(e) Item 5. WRITE DOWN THE NO-LOAD IDLE EGT - THE BLEED VALVE SWITCH FOR THE APU CLOSED - WITH A MINIMUM ELECTRICAL LOAD (SEE CHART A)
1) A low idle EGT can be caused by a problem with the EGT
indication system.
2) A high idle EGT can be caused by these items: a) A dirty compressor b) Dirty crossover ducts c) Damaged compressor wheels d) A clogged inlet e) A damaged diffuser section f) A damaged or a wrong combustor g) A damaged torus h) A damaged hot gas nozzle i) A damaged turbine wheel j) Leakage from the gasket between the plenum and the case 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 AIRBORNE AUXILIARY POWER 1(112)
