Underpressure Fault

TASK 21-58-00-810-816-A
Underpressure Fault

1. Possible Causes

SENSOR-PRESS,CSAS [117HW]
VALVE-ISOLATION,CSAS [111HW]
wiring
OZONE CONVERTER-ASSY,CSAS [5101HM]
EXCHANGER-HEAT,CSAS [5103HM]

2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	WATER - SOAPY SOLUTION

B. Consumable Materials

REFERENCE	DESIGNATION
(Material No.14CCB6)	Testing Medium-Leak Detection - Oxygen System

C. Referenced Information

REFERENCE	DESIGNATION
ASM 215301
AMM 21-58-00-710-002	Operational Test of the Conditioned Service Air System with Bleed Air
AMM 21-58-12-000-001	Removal of the Pressure Sensor
AMM 21-58-12-400-001	Installation of the Pressure Sensor
AMM 21-58-41-000-001	Removal of the CSAS Heat Exchanger
AMM 21-58-41-400-001	Installation of the CSAS Heat Exchanger
AMM 21-58-42-000-001	Removal of the Ozone Converter Assy
AMM 21-58-42-400-001	Installation of the Ozone Converter Assy
AMM 21-58-51-000-001	Removal of the CSAS Isolation Valve
AMM 21-58-51-400-001	Installation of the CSAS Isolation Valve

3. Fault Confirmation
Subtask 21-58-00-810-076-B ** ON A/C NOT FOR ALL

A. Access
(1) Get access to the components and ducts of the conditioned service air system (CSAS).

Subtask 21-58-00-710-080-B ** ON A/C NOT FOR ALL

B. Test.
(1) Apply a solution of Testing Medium-Leak Detection - Oxygen System (Material No.14CCB6) or WATER - SOAPY SOLUTION to all components and ducts of the conditioned service air system to search for a leak.
(2) Do the operational test of the conditioned service air system with bleed air AMM 21-58-00-710-002.
(3) Leak Check

Do a check for leakages at all components and ducts of the conditioned service air system while and immediately after the system test with bleed.

4. Fault Isolation
Subtask 21-58-00-810-088-A ** ON A/C NOT FOR ALL

A. If a leakage is found:

remove the leakage by replacement of the faulty component if necessary.

Subtask 21-58-00-810-097-B ** ON A/C NOT FOR ALL

B. If the test gives no failure message and no leakage at CSAS was found, no further trouble shooting is necessary.
(1) If the fault continues:
replace the SENSOR-PRESS,CSAS [117HW] AMM 21-58-12-000-001 AMM 21-58-12-400-001.

Subtask 21-58-00-810-090-B ** ON A/C NOT FOR ALL

C. If the test gives a different maintenance message, do the related trouble shooting procedure.

Subtask 21-58-00-810-077-B ** ON A/C NOT FOR ALL

D. If the test gives the maintenance message UNDERPRESS and no leakage was found:

replace the VALVE-ISOLATION,CSAS [111HW] AMM 21-58-51-000-001 and AMM 21-58-51-400-001.

(1) If the fault continues:

do a check and repair the wiring from:
the CSAS ISOLATION VALVE (111HW) AA to the CSAS CONTROL UNIT (100HW) AB/5A,
the CSAS ISOLATION VALVE (111HW) AH to the CSAS CONTROL UNIT (100HW) AB/8A and,
the CSAS ISOLATION VALVE (111HW) to ground ASM 215301.

(2) If the fault continues:

replace the OZONE CONVERTER-ASSY,CSAS [5101HM] AMM 21-58-42-000-001 and AMM 21-58-42-400-001.

(3) If the fault continues:

remove the Inlet Duct and Outlet Duct of the TCM (110HW).
do a visual inspection of the ducts and of the inside of the Heat Exchanger (5103HM).

(4) If the fault continues:

replace the EXCHANGER-HEAT,CSAS [5103HM] AMM 21-58-41-000-001 and AMM 21-58-41-400-001.

(5) If the fault continues:

do a check for leakages at all components and ducts of the fuel tank inerting system.

Subtask 21-58-00-710-081-A ** ON A/C NOT FOR ALL

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

[Rev.8 from Aug 2018] 2026.04.04 04:24:50 UTC