APU Fuel System - Low Pressure

TASK 28-22-00-810-801-A
APU Fuel System - Low Pressure

1. Possible Causes

PRESS SWITCH-APU FUEL PRESSURE [7QC]
RELAY 6QC
RELAY 5QC
RELAY 9QC
wiring
PUMP-APU FUEL [4QC]
RELAY 4KD
SWITCH-APU FUEL LP [5030QM]
wiring and connectors between the switch 5030QM and the ECB
ELECTRONIC CONTROL BOX [59KD]
VALVE-AIR RELEASE, L WING TK [86QM]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 28-21-41-000-001	Removal of the Low Pressure (LP) Air-Release-Valve 86QM(87QM)
AMM 28-21-41-400-001	Installation of the Low Pressure (LP) Air-Release-Valve 86QM(87QM)
ASM 282201
AMM 28-22-14-000-001	Removal of the APU Fuel LP-Switch
AMM 28-22-14-400-001	Installation of the APU Fuel LP-Switch
AMM 28-22-15-000-001	Removal of the APU Fuel Pressure Switch
AMM 28-22-15-400-001	Installation of the APU Fuel Pressure Switch
AMM 28-22-51-000-001	Removal of the APU Fuel Pump
AMM 28-22-51-400-001	Installation of the APU Fuel Pump
ASM 282901
AMM 49-31-00-710-001	Operational Test of the APU Fuel Low Pressure Circuit (GTCP 36-300)
AMM 49-31-00-710-002	Operational Test of the APU Fuel Low Pressure Circuit (APS 3200)
AMM 49-31-00-710-003	Operational Test of the APU-Fuel Low-Pressure Circuit ((131-9(A))
ASM 496102
AMM 49-61-34-000-003	Removal of the Electronic Control Box (ECB) (131-9(A))
AMM 49-61-34-400-003	Installation of the Electronic Control Box (ECB) (131-9(A))

3. Fault Confirmation
Subtask 28-22-00-710-050-A

A. Operational test
(1) Do the Operational Test of the APU Fuel Low Pressure Circuit:

for the GTCP 36-300 APU AMM 49-31-00-710-001,
or
for the APS 3200 APU AMM 49-31-00-710-002,
or
for the 131-9(A) APU AMM 49-31-00-710-003.

(2) Make sure that the subsequent system is serviceable before you start the fault isolation procedure:

the main fuel pump system (Ref. 28-21-00),
the APU LP fuel shutoff system (Ref. 28-29-00).

4. Fault Isolation
Subtask 28-22-00-810-051-A

A. If the test gives the subsequent results:
.on the lower ECAM display unit, the FUEL LO PR advisory is off with the L main fuel pump in operation,
.on the lower ECAM display unit, the FUEL LO PR advisory comes on and the APU fuel pump does not operate:

push the FUEL LINE pushbutton switch 8QC to operate the APU FUEL PUMP 4QC.

(1) If the APU FUEL PUMP 4QC operates:

Replace the PRESS SWITCH-APU FUEL PRESSURE [7QC] AMM 28-22-15-000-001 and AMM 28-22-15-400-001.

(a) If the fault continues:

Do a check of the RELAY 6QC and replace if necessary.

(b) If the fault continues:

Do a check of the RELAY 5QC and replace if necessary.

Do a check of the RELAY 9QC and replace if necessary.

(d) If the fault continues:

Do a check and repair the wiring from the:
CB 2QC to the RELAY 6QC A/B2,
RELAY 6QC A/C3 to the PRESS SWITCH 7QC A/B,
RELAY 5QC A/X1 to the PRESS SWITCH 7QC A/A,
RELAY 5QC A/X2 to the GND ASM 282201.

(2) If the APU FUEL PUMP 4QC does not operate:

replace the PUMP-APU FUEL [4QC] AMM 28-22-51-000-001 and AMM 28-22-51-400-001,
Push the FUEL LINE pushbutton switch 8QC again.

(a) If the fault continues:

Do a check of the RELAY 5QC and replace if necessary.

(b) If the fault continues:

Do a check of the RELAY 6QC and replace if necessary.

Do a check of the RELAY 9QC and replace if necessary.

(d) If the fault continues:

Do a check of the RELAY 4KD and replace if necessary.

(e) If the fault continues:

Do a check and repair the wiring from the:
CB 1QC to the RELAY 5QC A/B2 via the RELAY 9QC,
CB 2QC to the RELAY 9QC A/A1,
CB 2QC to the RELAY 9QC A/X1,
RELAY 5QC A/B1,A3 to the APU FUEL PUMP 4QC A/A,
RELAY 6QC A/B1 to the RELAY 5QC A/A2,
RELAY 6QC A/C2 to the CB 1QF via the RELAYs 4KD, 5WF, 6WF,
APU FUEL PUMP 4QC A/B to the GND ASM 282201 and ASM 282901.

Subtask 28-22-00-810-052-A

B. If the test gives on the lower ECAM display unit the FUEL LO PR advisory is on, but the test was correct with the L main fuel pump and the APU fuel pump:

replace the SWITCH-APU FUEL LP [5030QM] AMM 28-22-14-000-001 and AMM 28-22-14-400-001.

(1) If the fault continues, do a check and repair the wiring and connectors between the switch 5030QM and the ECB :
APU FUEL LP SWITCH 5030QM P17 to the ECB 59KD AB/B7,B8 ASM 496102.
(2) If the fault continues:

replace the ELECTRONIC CONTROL BOX [59KD] AMM 49-61-34-000-003 and AMM 49-61-34-400-003.

Subtask 28-22-00-810-054-A

C. If the fault continues:
(1) Replace the VALVE-AIR RELEASE, L WING TK [86QM] AMM 28-21-41-000-001 and AMM 28-21-41-400-001.

Subtask 28-22-00-710-051-A

D. Do the test given in Para. 3.

5. Close-up
Subtask 28-22-00-860-050-A

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:39:36 UTC