APU DISCH light is illuminated

TASK 26-22-00-810-806-A
APU DISCH light is illuminated

1. Possible Causes

BOTTLE-APU FIRE EXTING [11WF]
wiring
ENG/APU FIRE PNL [1WD]
SYS1/ESS TEST RELAY (46LP)

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 26-12-12-000-001	Removal of the ENG/APU Fire Panel
AMM 26-12-12-400-001	Installation of the ENG/APU Fire Panel
AMM 26-22-00-040-004	Bottle Pressure Check
AMM 26-22-00-710-001	Operational Test of the APU Fire-Extinguishing Loop/Squib
ASM 262201
AMM 26-22-41-000-001	Removal of the Fire Extinguisher Bottle
AMM 26-22-41-400-001	Installation of the Fire Extinguisher Bottle
AMM 26-22-43-960-001	Replacement of the Discharge Indicator Disc
ASM 331417

3. Fault Confirmation
Subtask 26-22-00-710-062-A

A. The APU FIRE EXTINGUISHING PANEL 20VU (p/n 330TS08Y) has a fault. Special operation is necessary. Incorrect operation causes the APU fire extinguisher bottle to discharge. Airbus supplies a new 20VU panel that corrects this fault. See TFU 26.22.00.007 for more data.
(1) Maintenance recommendation:
(a) Before the test:

Pull the CIRCUIT BREAKER 30WF on panel 120VU.

(b) During the test:

Push the APU FIRE TEST BUTTON quickly and fully.
Hold it fully during the test.
Release it quickly.

Close the CIRCUIT BREAKER 30WF on panel 120VU.

(2) Do the operational test of the APU fire-extinguishing system AMM 26-22-00-710-001.

4. Fault Isolation
Subtask 26-22-00-810-069-A

A. On the FIRE PANEL 20VU:
if the DISCH legend in the AGENT pushbutton switch stays on (is on):

Do a check if the red disk of the discharge indicator (4035WM) is visible.

(1) If the red disk is ruptured:

Do the bottle pressure check AMM 26-22-00-040-004.

(a) If the test is not OK:

Replace the BOTTLE-APU FIRE EXTING [11WF]
AMM 26-22-41-000-001 and AMM 26-22-41-400-001.
Do the replacement of the discharge indicator disc AMM 26-22-43-960-001.

(b) If the test is OK:

Do the replacement of the discharge indicator disc AMM 26-22-43-960-001.

(2) If the red disk is visible:

Get access to the APU compartment and do a check for signs of extiguisher agent.

(a) If there are signs of extinguisher agent in the APU compartment:

Replace the BOTTLE-APU FIRE EXTING [11WF]
AMM 26-22-41-000-001 and AMM 26-22-41-400-001.

(b) If there are no signs of extinguisher agent in the APU compartment:

Do the bottle pressure check AMM 26-22-00-040-004.

1 If the test is not OK:

Replace the BOTTLE-APU FIRE EXTING [11WF]
AMM 26-22-41-000-001 and AMM 26-22-41-400-001

2 If the test is OK:

Do a check and/or repair of the wiring from
FIRE EXTINGUISHING BOTTLE (11WF) 11WF-A/C to ENG/APU FIRE PANEL (1WD) 1WD-EE/K;
FIRE EXTINGUISHING BOTTLE (11WF) 11WF-A/B to GND;
ASM 262201.

a If the wiring is OK:

Replace the ENG/APU FIRE PNL [1WD]
AMM 26-12-12-000-001 and AMM 26-12-12-400-001.

b If the fault continues:

Replace the SYS1/ESS TEST RELAY (46LP).

c If the fault continues:

Do a check and/or repair of the wiring from
ENG/APU FIRE PANEL (1WD) 1WD-EE/L to SYS1/ESS TEST RELAY (46LP) 46LP-A/B1
ASM 331417.

Subtask 26-22-00-710-063-A

B. Do the test as given in the Para. 3.A.

[Rev.8 from Aug 2018] 2026.04.04 04:27:25 UTC