APU FIRE Signal Channel A and/or Channel B Fault

TASK 26-22-00-810-801-A
APU FIRE Signal Channel A and/or Channel B Fault

1. Possible Causes

DETECTOR-APU FIRE (LOOP A) [21WG]
DETECTOR-APU FIRE (LOOP B) [22WG]
FDU-APU [13WG]
wiring

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
ASM 261301
AMM 26-13-15-000-001	Removal of the Sensing Elements
AMM 26-13-15-400-001	Installation of the Sensing Elements
AMM 26-13-34-000-001	Removal of the APU Fire-Detection Unit (FDU)
AMM 26-13-34-400-001	Installation of the APU Fire-Detection Unit (FDU)
AMM 26-22-00-710-001	Operational Test of the APU Fire-Extinguishing Loop/Squib
AMM 31-50-00-710-001	Ground Scanning of the Central Warning System

3. Fault Confirmation
Subtask 26-22-00-710-050-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 26-22-00-810-050-A

A. If the test gives a different maintenance message:

Do the trouble shooting procedure related to the maintenance message.

Subtask 26-22-00-810-051-A

B. If the test gives the maintenance message APU FIRE and the both red light rows in the APU FIRE PUSH p/bsw (20VU) come on.

replace the DETECTOR-APU FIRE (LOOP A) [21WG] and/or DETECTOR-APU FIRE (LOOP B) [22WG] AMM 26-13-15-000-001 and AMM 26-13-15-400-001.

(1) If the fault continues:

replace the FDU-APU [13WG] AMM 26-13-34-000-001 and AMM 26-13-34-400-001.

(2) If the fault continues:

do the operational test of the central warning system AMM 31-50-00-710-001

(a) If the test gives a different maintenance message:

Do the trouble shooting procedure related to the maintenance message.

(3) If the fault continues:

do a check and repair the wiring if necessary between the:
FDU (13WG) connector A/K and DETECTOR (21WG) connector A/A,
FDU (13WG) connector A/J and DETECTOR (21WG) connector A/E,
FDU (13WG) connector B/K and DETECTOR (22WG) connector A/A,
FDU (13WG) connector B/J and DETECTOR (22WG) connector A/E ASM 261301.

(4) If the fault continues:

do a check and repair the wiring if necessary between the:
FDU (13WG) connector A/E and FWC (1WW1) connector AA/5C,
FDU (13WG) connector A/M and FWC (1WW1) connector AA/4E,
FDU (13WG) connector B/L and FWC (1WW1) connector AD/4G,
FDU (13WG) connector B/E and FWC (1WW1) connector AD/5E,
FDU (13WG) connector B/N and GND,
FDU (13WG) connector B/B and GND,
FDU (13WG) connector A/B and GND ASM 261301.

Subtask 26-22-00-710-056-A

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

5. Close-up
Subtask 26-22-00-860-050-A

A. Put the aircraft back to its initial configuration.

[Rev.8 from Aug 2018] 2026.04.04 04:27:24 UTC