*
Pack flow schedule 4 is not selected

*
Airplane is not in a stall condition

*
Left trim air switch is set to the ON position

*
Left trim air pressure sensor is not failed

*
One of both channels of the left CTC operates

*
No duct overheat condition in zones B, C, E, or F/D.

EFFECTIVITY
BEJ ALL

The usual pressure regulation value for the trim air PRSOV is 5 psi above cabin pressure.
The CTC can adjust the regulation value between 2 -8.5 psi above cabin pressure. The CTC can adjust the regulation value as necessary to control zone temperature. The CTC does this only when a trim air modulating valve fails more than 10 percent open. See the zone temperature control and indication section for more information about the control of the trim air modulating valves (SECTION 21-61).
Duct Overheat
A duct overheat (190F, 88C) for zones that get conditioned air from the mix manifold causes the related trim air PRSOV to latch closed. A duct overheat (190F, 88C) for the flight deck zone can operate one of these two ways:
*
If the left pack outlet temperature is less than 160F (71C), then the trim air PRSOV is latched closed

*
If the left pack outlet temperature is equal to or more than 160F (71C), then the trim air PRSOV closes but does not latch.

This type of control makes sure the left trim system does not latch off when the left pack gives air to the flight deck at a high temperature. See the pack cooling and mix manifold temperature control section for more information about the temperature control function of the air conditioning pack (SECTION 21-52).
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AIR CONDITIONING -TRIM AIR PRESS REGULATION AND SHUTOFF CTRL -FUNCTIONAL DESCRIPTION

ASCPC Control
The air supply cabin pressure controller (ASCPC) can close the trim air pressure regulating and shutoff valve to decrease the load on the pneumatic system. The ASCPC closes the valve if any of these conditions occur:
*
Airplane is in a stall condition

*
Left trim air switch is set to the out position.

For the trim air system, the stall condition has a maximum time limit of 8 seconds. After 8 second the trim system returns to normal operation.
ASCPC Preflight Test
Immediately after an engine start, the ASCPCs send flow schedule 1 to the CTCs. The CTCs set the trim air pressure regulating and shutoff valves to the open position while the ASCPC does a test of its control over these valves. When the ASCPC completes this test (15 sec), the CTC sets the valves to the correct position, and the ASCPC releases control.
EFFECTIVITY BEJ ALL  21-62-00 
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AIR CONDITIONING -TRIM AIR PRESS REGULATION AND SHUTOFF CTRL -FUNCTIONAL DESCRIPTION

EFFECTIVITY BEJ ALL  21-62-00 
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777 AIRCRAFT MAINTENANCE MANUAL

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21-73-00

Page 1 D633W101-BEJ Jan 05/2002

AIR CONDITIONING -OZONE CONTROL

Purpose
Ozone control keeps ozone concentrations in the air flow to a satisfactory limit when the airplane is at high altitudes.
Physical Description
The ozone converter has no moving parts. It contains a catalytic material through which the air flows.
Location
An ozone converter is part of each pack in the ECS bay. It attaches to the lower air ducts that supply each pack. The converter is aft of the lower flow control valve and below the upper flow control valve.
Functional Description
The ozone converter is a catalytic device that removes ozone concentrations. Air goes through the converter before it flows into the pack. A chemical reaction in the converter changes ozone molecules to oxygen molecules.
EFFECTIVITY BEJ ALL  21-73-00 
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D633W101-BEJ  Jan 05/2002 
BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details. 

777 AIRCRAFT MAINTENANCE MANUAL

AIR CONDITIONING -OZONE CONTROL

EFFECTIVITY BEJ ALL  21-73-00 
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