Failure of the Skin Exchanger-Outlet Bypass Valve

TASK 21-26-00-810-820-A
Failure of the Skin Exchanger-Outlet Bypass Valve

1. Possible Causes

VALVE-SKIN EXCHANGER OUTLET BYPASS, AVNCS VENT [23HQ]
wiring
AEVC [10HQ]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 21-26-00-710-001	Operational Check of the Avionics Equipment Ventilation-System via MCDU
AMM 21-26-00-710-008	Operational Test to Read the CFDS for CLASS 3 Faults of the AEVC
AMM 21-26-00-710-009	Operational Test to Read the CFDS for LAST LEG REPORT of the AEVC
ASM 212603
AMM 21-26-34-000-001	Removal of the Avionics Equipment Ventilation Computer (AEVC)
AMM 21-26-34-400-001	Installation of the Avionics Equipment Ventilation Computer (AEVC)
AMM 21-26-55-000-003	Removal of the Avionics Ventilation Skin Exchanger Outlet Bypass Valve
AMM 21-26-55-400-003	Installation of the Avionics Ventilation Skin Exchanger Outlet Bypass Valve

3. Fault Confirmation
Subtask 21-26-00-865-064-A

A. Table of the circuit breakers used in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C ALL
122VU	AIR COND/AVNCS/VENT/MONG	3HQ	Y17

Subtask 21-26-00-710-066-A

B. Test
(1) Do a reset of the AEVC (10HQ).
(a) Open the circuit breaker AIR COND/AVNCS/VENT/MONG (3HQ).
(b) Wait for five seconds.
(c) Close the circuit breaker AIR COND/AVNCS/VENT/MONG (3HQ).
(2) Do the operational test of the avionics equipment ventilation from the Multipurpose Control and Display Unit (MCDU) AMM 21-26-00-710-001.
(3) Read the LAST LEG REPORT of the AEVC AMM 21-26-00-710-009.
(4) Read the CLASS 3 faults of the AEVC AMM 21-26-00-710-008.

4. Fault Isolation
Subtask 21-26-00-810-058-A

A. If the test gives the maintenance message OUTLET BYPASS V 23HQ:

Do a check of the status of the skin exchanger-outlet bypass valve (23HQ) microswitches, between pin A/J and pin A/G and between pin A/M and pin A/K ASM 212603.

(1) If the status of the microswitch between pins A/J and A/G is equivalent to the status of the microswitch between pins A/M and A/K:

Replace the VALVE-SKIN EXCHANGER OUTLET BYPASS, AVNCS VENT [23HQ] AMM 21-26-55-000-003 and AMM 21-26-55-400-003.

(2) If the status of the microswitch between pins A/J and A/G is not equivalent to the status of the microswitch between pins A/M and A/K:

Do a check for a ground signal at pin A/U, pin A/G, and pin A/K of the skin exchanger-outlet bypass valve (23HQ) ASM 212603.

(a) If there is no ground signal:

Repair the related wiring.

(b) If there is a ground signal:

Do a check of the wiring between the AEVC (10HQ) and the skin exchanger-outlet bypass valve (23HQ) ASM 212603:
. Pin AB/6A and pin A/J
. Pin AB/6B and pin A/M.

1 If the wiring is not correct:

Repair the related wiring .

2 If the wiring is correct:

Do a check of the wiring between the AEVC (10HQ) and the skin exchanger-outlet bypass valve (23HQ) ASM 212603:
. Pin AA/6A to pin A/A
. Pin AA/6B to pin A/C.

a If the wiring is not correct:

Repair the related wiring .

b If the wiring is correct:

Replace the VALVE-SKIN EXCHANGER OUTLET BYPASS, AVNCS VENT [23HQ] AMM 21-26-55-000-003 and AMM 21-26-55-400-003.

(3) If the fault continues:

Replace the AEVC [10HQ] AMM 21-26-34-000-001 and AMM 21-26-34-400-001.

Subtask 21-26-00-710-067-A

B. Do the operational test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:24:38 UTC