(a)
Prepare to operate APU (AMM 49-11-0/201).
(b)
Position BATTERY switch to OFF and placard.
(c)
Open all fuel system boost pump circuit breakers on aft overhead panel P6-3.
(d)
Open APU compartment access door latches and open door. Install door support rods.
(e)
Support shroud, open shroud latches, and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
(f)
Remove cap from control air pressure port on fuel control unit.
(g)
Disconnect high pressure fuel supply line at fuel atomizer assembly.
(h)
Connect test pressure gage to high pressure fuel supply line.
(i)
Close the fuel system boost pump circuit breakers.
(j)
Position BATTERY switch to ON and remove placard.
(2)
Test fuel control unit acceleration limiter valve cracking pressure (opening).
(a)
Position APU master switch to START and release.
NOTE: APU master switch will return to ON. Engine motoring will begin after air inlet door and APU fuel valve have opened. Make sure the fuel boost pump is operating. After approximately 90 seconds of motoring, motoring is terminated by a time limiting device in APU control unit.
(b)
While engine is motoring, loosen fuel line nut at pressure test gage, and bleed trapped air from line and tighten nut. As engine rpm stabilizes, observe acceleration limiter valve cracking pressure. Cracking pressure should be 60 +3 psig for Non-TAFCU or 60 ±5 psig for TAFCU.
(d)
FUEL CONTROL UNIT WITHOUT THE TIMED ACCELERATION CONTROL; If cracking pressure is to low, replace fuel control unit. If the cracking pressure is greater then 60 ±3 psig, adjust the acceleration limiter valve as follows: 1) Remove the lockwire from the locknut for the valve adjustment screw. 2) Loosen the locknut for the valve adjustment screw. 3) If the cracking pressure is too high, turn the valve adjustment screw
581
May 01/99 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-11-0 Page 502A
counterclockwise.
NOTE: A full turn of the adjustment screw is the same as approximately 8-10 psig change.
4) Tighten the locknut for the valve adjustment screw.
5) Install a lockwire on the locknut for the valve adjustment screw.
(e)
FUEL CONTROL UNIT WITH THE TIMED ACCELERATION CONTROL; If the cracking pressure is more than 65 psig (448 kPa), or less than 55 psig (380 kPa), replace the timed acceleration fuel control unit (AMM 49-31-11/401).
(f)
Position APU master switch to OFF.
(g)
After the air inlet door closes, do the above test steps (a) and (c) thru (g) until the limiter valve adjustment is correct.
CAUTION: DO NOT EXCEED STARTER MOTOR DUTY CYCLE
(AMM 49-11-0/201).
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49-11-0 Page 502B BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/99
F07272
503 Fuel Control Unit Adjustment
Aug 01/95 Figure 501 49-11-0
Page 503
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(3) Restore airplane to normal configuration (Fig. 501).
(a)
Position BATTERY switch to OFF and placard.
(b)
Open the fuel boost pumps circuit breakers.
(c)
Disconnect test pressure gage from high-pressure fuel line.
(d)
Connect high-pressure fuel line at fuel atomizer assembly.
(e)
Install cap on control air pressure port on fuel control unit.
(f)
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.
(g)
Disengage APU compartment access door support rods and stow rods. Close and latch access door.
(h)
Remove placard from BATTERY switch.
(i)
Activate fuel boost pumps as required.
D. Test Fuel Control Unit Governor Speed Setting - NO LOAD
NOTE: It is not necessary to do the governor speed setting test for the fuel control unit after you replace the APU, fuel control unit or bleed air valve. You can use this test for troubleshooting and governor speed adjustment of the fuel control unit.
(1)
Position BATTERY switch to OFF and placard.
(2)
Open APU compartment access door latches and open door. Install door support rods.
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