*
Stall recovery

*
Trim air pressure sensor failed

*
Trim air switch set to OFF

*
Duct temperature greater than 190F (88C).

Both trim air pressure regulating and shutoff valves function if at least one pack operates.
When the APU supplies air for pack operation and airplane ventilation, the CTCs tell the APUC the quantity of air to supply with the APU DEMAND signal. See the zone temperature control and indication section for more information about the APU DEMAND signal (SECTION 21-61).
Non-Normal Function
These conditions cause non-normal operations:
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AIR CONDITIONING -TEMPERATURE CONTROL -FUNCTIONAL DESCRIPTION

*
Loss of left side trim

*
Loss of right side trim

*
Overheat conditions (190F, 88C)

*
Single trim modulating valve failure.

Loss of Left Side Trim
If there is a failure of the left side trim system, the left CTC sets the left pack to hold the flight deck target temperature. The right CTC sets the right pack to hold the necessary mix manifold temperature.
The left CTC decreases or increases the flight deck target temperature up to a maximum of 5F (3C) for any of these conditions:
*
Average cabin zone temperature is 2F (1C) above or below the average target temperature

*
Single cabin zone temperature is 5F (3C) above or below its target temperature.

This type of control lets the cabin area have priority over the flight deck. It does this when the right pack and right trim system does not keep the cabin areas at the necessary temperatures.
Loss of Right Side Trim
If there is a failure of the right side trim system, The right CTC sets the right pack to hold the necessary mix manifold temperature. The left pack follows the right pack until flight deck trim modulating valve is closed. The left CTC then controls the left pack to keep the flight deck at the target temperature down to a minimum of 65F (18C).
The left CTC does not keep the flight deck at its target temperature if the right pack operates at full heat and any of these conditions occur:
*
Average cabin zone temperature is 5F (3C) below the average reference temperature

*
Single cabin zone temperature is 5F (3C) below its target temperature.

When the right pack does not keep the cabin area at the necessary temperature, the left CTC increases the flight deck target temperature up to a maximum of 5F (3C).
Overheat Conditions
The applicable CTC starts to close the trim air modulating valve if the related zone duct air temperature increases to 160F (71C). The related trim air pressure regulating and shutoff valve latches closed if duct temperature increases to 190F (88C) for 10 seconds.
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AIR CONDITIONING -TEMPERATURE CONTROL -FUNCTIONAL DESCRIPTION

Single Trim Modulating Valve Failure
If a trim air modulating valve is not fully closed and has a failure, the applicable CTC controls the pressure reference for the related trim air pressure regulating and shutoff valve to keep zone duct temperature to a limit (zone duct temperature backup control mode). The applicable CTC does not use this mode if the valve is less than 10 degrees open (1 percent heating) and has a failure.
If the RVDT in a valve has a failure, The applicable CTC operates the valve with no position feedback. This type of control is called open loop control. The applicable CTC looks at temperature change downstream of a valve to monitor movement.
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AIR CONDITIONING -TEMPERATURE CONTROL -FUNCTIONAL DESCRIPTION

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777 AIRCRAFT MAINTENANCE MANUAL

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AIR CONDITIONING -TEMPERATURE CONTROL -OPERATION -FLIGHT DECK

General
The air conditioning panel has these controls for temperature control operation:
*
Left and right trim air switches

*
Flight deck temperature control

*
Cabin temperature control

*
Air conditioning reset switch.

Location
The air conditioning panel is on the P5 overhead panel in the flight deck.
Trim Air Control
L and R TRIM AIR switches are alternate-action switches. ON shows when you push the switch in for automatic operation of the trim system.
The applicable FAULT light and the applicable advisory message TRIM AIR L (R) (not shown) are not a function of switch position. They show when any of these conditions occur:
　
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