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8.5 psi above cabin pressure. The usual pressure is 5 psi above cabin pressure. This allows sufficient flow and keeps pneumatic system noise to a minimum. The trim air pressure sensors give trim air pressure information to the cabin temperature controllers (not shown) for control and indication.
Zone Temperature Control
The cabin temperature controllers use the packs to control cooling for the flight deck and the mix manifold.
The trim air modulating valves control the quantity of trim air supplied to each zone. Trim air for the passenger zones mixes with the air from the mix manifold. Trim air for the flight deck mixes with the air from the left pack.
Each trim air modulating valve adjusts the amount of trim air to control the zone temperature. Zones that need a higher temperature get more trim air. Zones that need a lower temperature get less trim air.
The zone air temperature sensors and zone duct temperature sensors give air temperature information to the cabin temperature controllers (not shown) for control and indication.
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AIR CONDITIONING -TEMPERATURE CONTROL -GENERAL DESCRIPTION -MECHANICAL

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AIR CONDITIONING -TEMPERATURE CONTROL -INTERFACES

Interfaces
These systems have an interface with the CTC on the systems ARINC 629 buses:
*
Airplane information management system (AIMS): ground test, indication and fault monitoring

*
Air ground system (AGS): air/ground information

*
Cabin services system (CSS): cabin selected temperatures

*
APU controller (APUC): quantity of air necessary for zone temperature control and ventilation (APU demand signal)

*
Environmental control system miscellaneous cards
(ECSMCs): lavatory/galley ventilation fan status (on/off)

*
Air supply cabin pressure controller (ASCPC): flow schedules, stall condition, altitude

*
Overhead panel ARINC 629 system (OPAS): flight deck temperature control, passenger cabin temperature control, trim air control, trim air fault indications, air conditioning reset.

The CTC supplies analog control signals to these components:
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Trim air pressure regulating and shutoff valves

*
Zone trim air modulating valves.

These components supply analog data to the CTC:
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Zone trim air modulating valve RVDTs

*
Zone temperature sensors

*
Zone duct temperature sensors

*
Trim air pressure sensor.

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AIR CONDITIONING -TEMPERATURE CONTROL -INTERFACES

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AIR CONDITIONING -TEMPERATURE CONTROL -FUNCTIONAL DESCRIPTION

General
Warm trim air from the pneumatic system mixes with cold air from the mix manifold to keep each zone temperature at its target value. The cabin temperature controllers (CTCs) use the trim air pressure regulating and shutoff valves (PRSOVs) to keep the trim air pressure between 2 and 8.5 psi above cabin pressure. The CTCs control the trim air modulating valves to add the necessary quantity of warm air for zone temperature control.
The CTCs use sensors in the ducts and at zone locations to monitor air temperature for control.
The CTCs sets the packs to supply the coldest air necessary for the zone that needs the lowest mix manifold temperature. Zones that need higher temperatures get pack air mixed with trim air. The CTCs set each trim air modulating valve to keep the related zone at its target temperature.
Normal Function
The flight crew sets target temperatures for the flight deck and the master temperature for the passenger cabin. The minimum selectable temperature is 65F (18C) and the maximum is 85F (29C). The cabin crew can adjust the target temperature for each zone in the passenger cabin. This temperature can be 10F (6C) higher or lower than the master temperature set by the flight crew.
Immediately after an engine start, the ASCPCs send flow schedule 1 to the CTC. The CTC sets the trim air pressure regulating and shutoff valves to the open position while the ASCPC tests its control over these valves. When the ASCPC completes this test, the CTC sets the valves to the correct position, and the ASCPC releases control. The usual pressure for the trim air PRSOVs is 5 psi above cabin pressure.
The CTC closes the trim air pressure regulating and shutoff valves for these conditions:
*
CTC channel 1 and 2 failed

*
Pack flow at flow schedule 4
　
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