(a) E3-3 Electrical Shelf, APU Control Unit
(10)
Set the APU master switch to the ON position.
NOTE: Do not move the APU master switch to the START position. It is not necessary to start the APU.
(11)
Monitor the fuel pressure to make sure there are no leaks:
(a)
Make sure the fuel pressure at the pressure gage is approximately 20 psig (138 kPa).
(b)
Set the No. 1 AFT FUEL PUMPS switch, on the P5 forward overhead panel, to the OFF position.
(c)
Make sure the fuel pressure at the pressure gage does not decrease: 1) Monitor the fuel pressure on the pressure gage for 5 minutes. 2) If there is not a decrease in pressure during the five minute time, then these
check valves do not have leakage:
a) APU Primary Check Valve
b) APU Bypass Check Valve
c) APU Pressure Relief Valve (if installed)
3) If there is a decrease in fuel pressure, then do these steps to isolate the leakage in the APU fuel system: a) Set the No. 1 AFT FUEL PUMPS switch on the P5 overhead panel to the
ON position. b) Make sure the pressure on the pressure gage is approximately 20 psig. c) Set the APU master switch to the OFF position. d) Set the No. 1 AFT FUEL PUMPS switch, on the P5 forward overhead
panel, to the OFF position. e) Monitor the fuel pressure on the pressure gage for 5 minutes. f) If there is a decrease in fuel pressure, correct all leaks or damage to the
APU fuel system between the APU shutoff valve and the APU.
g) If there is no decrease in fuel pressure, then after you complete this procedure, do the procedure described below: "Leak Check of the APU Bypass Check Valve and Pressure Relief Valve".
(d) Loosen the nut on the hose to bleed the fuel pressure.
(12)
Remove the external electrical power from the airplane (AMM 28-24-0/201).
(13)
Make sure the APU master switch is set to OFF.
(14)
Open this circuit breaker and attach a DO-NOT-CLOSE tag:
(a) E3-3 Electrical Shelf, APU Control Unit
(15)
Remove the equipment from the fuel line:
(a)
Remove the pressure gage from the hose.
(b)
Remove the hose from the tee fitting.
(c)
Remove the fuel supply hose from the tee fitting.
(d)
Remove the tee fitting from the inlet fuel tube.
(e)
Install the fuel supply hose on the inlet fuel tube of the fuel control and pump assembly.
(16)
Do these steps to install the lower APU shroud:
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28-22-0 Page 207
CAUTION: KEEP A MINIMUM CLEARANCE OF 0.18 INCH (5 MM) BETWEEN THE ENGINE, FIRE DETECTOR, CLAMPS, AND LOWER SHROUD. BE CAREFUL WHEN YOU MOVE THE LOWER SHROUD. DAMAGE TO THE SHROUD DRAIN LINES CAN OCCUR.
(a)
Hold the lower shroud against the upper shroud.
(b)
Close the shroud latches.
(17)
Close the APU cowl door:
(a)
Disconnect the door support rods.
(b)
Put the door support rods in the clips on the APU cowl door.
(c)
Close the APU cowl door.
(d)
Close the latches for the APU cowl door.
(18)
Remove the DO-NOT-CLOSE tag and close this circuit breaker:
(a) E3-3 Electrical Shelf, APU Control Unit
(19)
Make sure the APU master switch is set to OFF.
D. Leak Check for the APU Bypass Valve and the Pressure Relief Valve (If Installed)
(1)
Set the APU master switch, on the P5 forward overhead panel, to the OFF position and attach a DO-NOT-OPERATE tag.
(2)
Set the No. 1 AFT FUEL PUMP switch, on the P5 forward overhead panel, to the OFF position.
(3)
Open this circuit breaker and attach a DO-NOT-CLOSE tag:
(a) E3-3 Electrical Shelf, APU Control Unit
(4)
Supply external electrical power to the airplane (AMM 24-22-0/201).
(5)
Set the L CTR FUEL PUMPS switch to ON.
(a) To operate any of the fuel boost pumps, you must be in the flight compartment to continuously monitor the fuel quantity and the low pressure indication in the fuel tank.
WARNING: DO NOT OPERATE ANY FUEL BOOST PUMP IF THE LOW PRESSURE LIGHT COMES ON AND STAYS ON. FUEL VAPORS IN THE TANK MAY IGNITE AND CAUSE A FIRE OR EXPLOSION.
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