APU Control Thermostat Installation 575
49-52-32Page 402 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Nov 15/78
APU CONTROL THERMOSTAT - ADJUSTMENT/TEST
1. General
A. These adjustment procedures apply to the APU control thermostat using an adjustment nut having a different thread pitch on either end. This thread differential in the nut provides the in or out movement of the valve assembly. Each revolution of the nut moves the valve assembly in or out by the differences between the pitches of the two threads.
B. After installation of control thermostat, operate APU, both air/conditioning packs, and observe EGT and bleed air duct pressure. If EGT is not within the range of 620°C and 650°C, the thermostat should be adjusted.
C. There are two adjustment/test procedures for the APU control thermostat. The first procedure uses the airplane instrumentation. The second procedure uses the thermostat calibration kit. You can use one of the two tests to adjust the APU control thermostat.
NOTE: Prior to performing check and calibration procedure for the APU control thermostat, make sure the outlet pressure for the air pressure regulator is within the limits (AMM 49-52-21/501). A high outlet pressure will, in effect, increase the thermostat setting; a low output pressure will, in effect, decrease the thermostat setting.
NOTE: For extended APU service life, the EGT set-point is set at the lower EGT limit range of 580-600°C (1076-1112°F). A lower EGT set-point may cause main engine start problems. A higher EGT set-point will correct the main engine start problems. The EGT set-point must not be more than 650°C (1202°F). The recommended EGT limit range is 620-650°C (1148-1202°F).
2. Equipment and Materials
A. Torque wrench - 0 to 100 pound-inches
B. Thermostat Calibration Kit - 834698-1, Griffith Enterprises, 300 East Cherry, Cottonwood, AZ 86326 (test using thermostat calibration kit)
C. Thermostat Calibration Kit - 290417-2-1, AlliedSignal, Inc., Airline Services Division, P.O. Box 52170, Phoenix, AZ 85072-2170 (This is an alternative to the thermostat calibration kit 834698-1.)
D. Thermostat Calibration Kit - 833657-1, AlliedSignal, Inc., Airline Services Division, P.O. Box 52170, Phoenix, AZ 85072-2170 (This is an alternative to the thermostat calibration kit 834698-1.)
3. Prepare to Adjust APU Control Thermostat (Using Airplane Instrumentation)
A. Operate APU (AMM 49-11-0/201).
CAUTION: TO AVOID DAMAGING APU, OBSERVE OPERATING LIMITS (AMM 49-11-0/201).
575
Aug 01/94 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-52-32 Page 501
(1) With "no load" applied, engine speed should stabilize at 405-410 CPS as indicated on generator frequency meter.
B. Observe airplane EGT and duct pressure indicator.
NOTE: Gas turbine engine tester may be used to indicate APU EGT. For tester installation, refer to AMM 49-21-0/501.
(1)
Position engines 1 and 2 BLEED switches (located on the P5 forward overhead panel) to OFF.
(2)
Position air conditioning L PACK and R PACK valve switches to ON.
(3)
Check that ISOLATION VALVE is in AUTO position.
(4)
On forward overhead panel, position APU BLEED AIR valve switch to ON.
(5)
Observe engine frequency on frequency meter at load application.
(6)
Move air conditioning control cabin temperature selector to MANUAL COLD until air mix valves indicate COLD.
(7)
Observe engine speed at full bleed load operation on frequency meter. Stabilized generator frequency under load should not be more than 10 CPS below that observed in step 3.A.(1).
(8)
Incrementally add 60 amps electrical load to APU generator.
(9)
Observe engine exhaust gas temperature on indicator at full bleed air load operation ("loaded" condition). This temperature is controlled by APU (load) control thermostat and should stabilize between 620°C and 650°C.
(10)
Remove electrical load (as required).
(11)
Position air conditioning R PACK and L PACK valve switches to OFF.
(12)
Position APU BLEED AIR valve switch to OFF.
(13)
Allow engine to operate at “”no load”” governed frequency for one minute (minimum).
(14)
Position APU master switch to OFF.
(15)
If EGT in step (9) was not met, adjust control thermostat per par. 5.
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