(3)
Position APU BLEED valve switch to ON.
(4)
Position L or R PACK switch to ON and note pneumatic pressure.
E. Confirm that APU is not delivering bleed air (i.e., no duct pressure and/or no rise in EGT). Overtemperature control switch, along with load control thermostat and thermostat selector solenoid valve integrity has been confirmed.
F. Shut down APU (AMM 49-11-0/201).
G. Reconnect lead to J1 receptacle of overtemperature control switch and lockwire.
H. Restore Airplane to Normal Configuration
(1) Position lower shroud against upper shroud and close shroud latches.
CAUTION: MAINTAIN A MINIMUM CLEARANCE OF 0.18 INCH BETWEEN ENGINE PLUMBING, FIRE DETECTOR, CLAMPS AND INSIDE SURFACE OF LOWER SHROUD.
EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
(2) Disengage APU compartment access door support rods and stow rods. Close and latch access door.
3. Adjust Overtemperature Control Switch (Fig. 501)
A. Equipment and Materials:
(1)
Thermostat Calibration Kit, P/N 290417-2-1
(2)
Thermocouple (Test) Assembly, P/N 290416-2
(3)
Cable Assembly (Thermocouple to Calibration Kit)
(4)
Temperature, Indicator, P/N 287512-1-1
(5)
Sealing Compound – Mold-Seal (TC 527)
B. Adjust Overtemperature Control Switch.
(1)
Gain access to overtemperature control switch in APU compartment.
(2)
Remove engine EGT thermocouple probe and replace with test thermocouple from thermostat calibration kit.
(3)
Connect cable assembly to test thermocouple and receptacle on calibration kit.
(4)
Remove control air line from APU control thermostat and bulkhead fitting on tailpipe heat shield.
(5)
Remove control thermostat from APU.
CAUTION: SUBJECTING CONTROL THERMOSTAT TO SLIGHTLY HIGHER THAN NORMAL TEMPERATURES WILL REDUCE SERVICE LIFE OF PART AND MAY ALTER SET POINTS OF THERMOSTAT.
(6)
Connect flexible line between bulkhead fitting on tailpipe heat shield and fitting on calibration kit. Open calibration kit needle valve to full open position.
(7)
Connect test temperature indicator to receptacle J3 of overtemperature control switch.
(8)
Start APU (AMM 49-11-0/201). Allow engine to accelerate to no-load, governed speed, at the same time closing calibration kit needle valve slowly to get APU to idle speed.
(9)
Position APU bleed air switch to ON.
(10)
Position L PACK and R PACK switches to ON.
(11)
Using calibration kit, slowly close needle valve until EGT stabilizes at 635 to 639°C (1175 to 1200°F).
(12)
Compare EGT readings at calibration kit indicator and test temperature indicator connected in (7). EGT indications shall compare within +6/-6°C (+10/-10°F). If temperatures do not compare within specified limits, adjust as follows:
(a)
Remove end plate from overtemperature control.
(b)
Using a jewelers type screwdriver, turn temperature indicator adjustment screw until EGT indicators (calibration kit and test temperature indicator) compare within specified limit.
NOTE: Each scale division represents approximately 17°C (30°F).
(c)
Recheck indicator comparison two successive times to ensure correct EGT readings by opening needle valve and repeating steps (11) and (12).
(13)
With APU bleed air valve in ON position, slowly close calibration kit needle valve at a rate of 3°C (5°F) per second until overtemperature control trip point is reached or maximum trip point overtemperature specified in Table 1 is indicated on temperature gage.
NOTE: The overtemperature trip point will be noted by a drop in exhaust gas
temperature (APU bleed air valve closes).
(14)
Record trip point and remove load from engine.
(15)
If trip point is not reached and not within limits of Table 1, the overtemperature control must be adjusted as follows:
(a)
Remove end plate from overtemperature control.
(b)
Using a jewelers screwdriver, turn adjustment screw until trip point is within specified limits. Each scale division represents approximately 17°C (30°F).
(c)
Recheck trip point setting by repeating steps (13) and (14) two successive times.
(16)
Position L PACK and R PACK switches to OFF.
(17)
Shut down APU (AMM 49-11-0/201).
501
Feb 01/96 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-52-81 Page 501
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