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sensors. Each temperature selector switch also has an OFF
position that removes trim air from the associated zone.
The TRIM AIR switch is in the ON position for normal operation.
Putting the TRIM AIR switch in the OFF position disables the
trim air supply to all zones.
AIR CONDITIONING - TEMPERATURE CONTROL - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-60-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-60-00-826
Operation
The temperature control system operates when the pack Flow
Control and Shutoff Valve is open and there are no critical fault
conditions. The air conditioning accessory units (ACAU) provide
the discrete outputs that enable or disable operation of the
cooling pack and the temperature control system components.
The TRIM AIR switch is in the ON position for normal operation.
This causes the Trim Air Pressure Regulating and Shutoff Valve
(PRSOV) to open and regulate the pressure in the trim air ducts
to approximately 4 psi above the cabin pressure. Putting the
TRIM AIR switch in the OFF position closes the Trim Air PRSOV
to disable the trim air supply to all zones.
The temperature selector switches allow a range of desired
temperature settings from approximately 65F to 85F (18C to
29C). There is also an OFF position for each temperature
selector switch that closes the associated zone trim air
modulating valve to remove the trim air supply from the zone.
For normal operation, the CTC calculates the correct pack outlet
temperature for the zone with the lowest temperature setting.
Both packs are controlled to provide the pack outlet
temperature that matches the zone with the lowest setting.
Hot trim air is supplied to the other two zones by the trim air
modulating valves to increase the supply duct air temperature
to match the desired zone temperature.
If the CTC detects a fault associated with the flight compartment
trim air supply, then the trim air system operates in the split
packs mode. In this mode, the left pack outlet temperature is
controlled to match the temperature setting for the flight
compartment and the right pack outlet temperature is
controlled to match the lower of the temperature settings for
the forward and aft passenger compartments. Hot trim air is
supplied to the other passenger cabin zone to increase its
supply duct air temperature to match the desired zone
temperature.
If the CTC detects a fault associated with the passenger cabin
trim air supply, or if the trim air supply is selected off, then the
trim air system operates in the average zone mode. In this
mode, the left pack outlet temperature is controlled to match the
temperature setting for the flight compartment and the right
pack outlet temperature is controlled to match the average of
the temperature settings for the forward and aft passenger
compartments. Trim air is commanded off.
Each CTC provides the following functions:
* Control of the pack outlet temperature by positioning the
temperature control valve (TCV)
* Standby control of the opposite pack outlet temperature by
positioning the standby TCV
* Control of the pack compressor temperature by modulating
the ram air flow
* Control of the cabin zone temperature to values between 65F
and 85F (18C to 29C)
AIR CONDITIONING - TEMPERATURE CONTROL - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-60-00
Page 77
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-60-00-826
* Control of the zone supply duct temperature to values
between 35F and 145F (2C and 63C)
* Automatic reconfiguration of standby and backup functions
for fault conditions
* Automatic fault detection and fault isolation of associated
components (BITE)
* Output of system status information for display on the P5
temperature control panel.
Indication
The TEMP (temperature) indicator can show the temperature in
any of these areas:
* Control cabin supply duct
* Forward passenger cabin supply duct
* Aft passenger cabin supply duct
* Forward cabin zone
* Aft passenger cabin zone
* Left pack outlet
* Right pack outlet.
. The AIR TEMP selector switch connects different temperature
sensors to the indicator to provide the desired indication.
If the temperature in a zone distribution duct is more than 190F
(88C), the duct overheat switch sends a signal to the ACAU. The
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