COND TRIM AIR SYS FAULT

ATA21

In the absence of air, a spring keeps the valve closed. This pneumatically-operated and
electrically-controlled valve regulates hot air pressure, which is tapped upstream of the packs. The
air conditioning system controller 1 regulates this valve. This valve closes upon pressing the HOT
AIR pushbutton on the AIR COND panel, or when both lanes of one air conditioning system controller(ACSC )
fail.
The valve closes automatically, if:
‐ The duct overheats, or
‐ The cockpit trim air valve fails, or
‐ Both cabin trim air valves fail.
The hot-air pressure-regulating valve remains operative, even if either the forward or aft cabin trim air
valve fails.

  • Do the operational test of the cockpit and cabin temperature-control system with CFDS/MCDU Ref. AMM 21-63-00-710-004 :
    • the HOT AIR pushbutton switch is in the on position (the FAULT and OFF legends are off).
    • the PACK 1 and the PACK 2 pushbutton switches are in the off position (the OFF legends are on).
    • On the CARGO HEAT panel 22VU, make sure that the HOT AIR pushbutton switch is in the on position (the FAULT and OFF legends are off).
  • If the test gives the maintenance message TRIM AIR PRESS VALVE OR PRESS SWITCH :
    • replace the TRIM AIR PRESS SWITCH (26HK).
    • If the fault continues: check wiring
    • If the fault continues: replace the TRIM AIR PRESS VALVE (14HK)
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