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WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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07/06/21

Message Overview:

Message Name:

FWD WATER SYSTEM TANK PURGES WHEN FWD LINE PURGE SELECTED

Message Code: 381OBS004
Effectivity: 9002, 9024, 9046, 9048, 9049, 9054, 9063, 9072, 9073, 9077, 9078, 9080, 9085, 9091, 9098, 9105 and 9108
System: Potable Water System
System Description: 38-10-00
Schematic Diagram: None
Wiring Diagram: None

Message Description:

While performing the Forward Water System LINE PURGE function, the Forward Water Tank also drains.

Possible Causes:

  • FWD Tank Valve Actuator (V3)
  • FWD Tank Valve Relay (KMW151)
  • External Water Service Panel
  • FWD Control Module (AMC157)
  • Auxiliary Power Unit (APU) Start Contactor Assembly (ASCA) (A48)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the APU Starter-Contactor Assembly AMM 24-62-05-000-801 [ Global Express ]  [ G5000 ]  [ Global XRS ]
Installation of the APU Starter-Contactor Assembly AMM 24-62-05-400-801 [ Global Express ]  [ G5000 ]  [ Global XRS ]
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02 [ Global Express ]  [ G5000 ]  [ Global XRS ]

Troubleshooting Recommendations:

NOTE: Take note if the issue is only present using the external water service panel, the galley touchscreen or using both.

NOTE: Apply power to the aircraft and make sure the forward water system is serviced properly.

NOTE: For wiring checks, refer to supplemental wiring diagrams "W/D Water System" and "W/D Water Level Indication".

  1. Using the external water system service panel or using the galley touchscreen water system functions, select FWD System Line Purge. Access the FWD TANK VALVE ACTUATOR (V3) connector and verify that 28 VDC is present at connector pin 2.

    1. If 28 VDC is not present, go to step 3.
    2. If 28 VDC is present and the issue is still present (valve open), continue with next step.

  2. Perform a continuity check between FWD TANK VALVE ACTUATOR (V3) connector pin 3 and ground.

    1. If there is continuity, repair defective wiring as required and do close out.
    2. If there is no continuity, replace the FWD TANK VALVE ACTUATOR (V3) and continue with next step.

  3. Remove the FWD TANK VALVE RELAY (KMW151) and verify that 28 VDC is present at pin A2.

    1. If 28 VDC is not present, go to step 8.
    2. If 28 VDC is present, continue with next step.

  4. While the FWD TANK VALVE RELAY (KMW151) is still removed, install a wire jumper between contacts A2 and A3 of the relay receptacle. Does the FWD TANK VALVE ACTUATOR (V3) close?

    1. If NO, go to step 10.
    2. If YES, continue with next step.
      NOTE: The FWD TANK VALVE RELAY (KMW151) is energized when "FWD FILL" or "FWD SYSTEM PURGE" is selected. In "FWD LINE PURGE" mode, the relay should be in a relaxed state. It means no 28 VDC present at relay coil X1 but it is normal to find a ground at relay coil X2.

  5. While the FWD TANK VALVE RELAY (KMW151) is still removed, check if 28 VDC is present at relay coil contact X1. There should be no voltage.

    1. If 28 VDC is not present and step 4 was successful, replace the FWD TANK VALVE RELAY (KMW151) and do close out.
    2. If 28 VDC is present, make sure that the water panel selector is still set to "FWD Line Purge" and continue with next step.

  6. While "FWD Line Purge" is still selected, verify that power is not present at the "FWD Fill" or "FWD SYSTEM PURGE" output pins at the External Service Panel connector.

    1. If power is present, replace the external Water Service Panel and do close out.
    2. If power is still present after replacing the panel (power at FWD TANK VALVE RELAY (KMW151) coil contact X1), continue with next step.

  7. Remove the FWD Control Module (MHC) connector (AMC157-1P1) and verify if the power is still present at the FWD TANK VALVE RELAY (KMW151) relay coil contact X1.

    1. If power is no longer present, replace the FWD control module (MHC) and do close out.
    2. If power is still present, continue with next step.

  8. Access the rear bay. Check and make sure the "WATER SERVICE" thermal circuit breaker on the ASCA is set IN.

    1. If the circuit breaker is OUT, investigate the reason and set it back to IN and do close out.
    2. If the circuit breaker is set to IN and the issue is still present (no power at FWD TANK VALVE RELAY (KMW151) pin A2) or the circuit breaker keeps popping out, continue with next step.

  9. Perform a wiring check between the ASCA "WATER SERVICE" circuit breaker and the FWD TANK VALVE RELAY (KMW151) pin A2.

    1. If wiring checks are not good, repair defective wiring as required and do close out.
    2. If wiring checks are good, continue with next step.

  10. Perform a wiring check between the FWD TANK VALVE RELAY (KMW151) pin A3 and the FWD TANK VALVE ACTUATOR (V3) connector pin 2.

    1. If wiring defects are found, repair defective wiring as required and do close out.
    2. If wiring checks are good, continue with next step.

  11. Replace the "WATER SERVICE" thermal circuit breaker on the ASCA. Is the fault still present?

    1. If NO, do close out.
    2. If YES, continue with next step.

  12. Replace the ASCA.
  13. Do close out.

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