(3)
Flight Deck
(a)
Flight deck temperature is selected with the FLT DECK selector on the cabin temperature control module. The ZTC compares the selected temperature with the signal from the flight deck zone temperature sensor and duct temperature sensor. The ZTC drives the flight deck trim air modulating valve more open or more closed in order to force sensed temperature to agree with selected temperature.
(b)
If the ZTC fails to regulate flight deck temperature correctly, the flight deck trim air modulating valve may be placed under manual control. When the FLT DECK selector is placed in the MAN position, the ZTC is bypassed. The selector may be held toward W to drive the trim air modulating valve more open, or held toward C to drive the valve more closed.
(4)
Upper Deck and Crew Rest Area
(a)
The upper deck and crew rest area compartment zone temperatures are selected with the digital cabin temperature selector.
(b)
The ZTC compares the overall selected temperatures for each zone with the signals from the zone temperature sensors and the duct temperature sensors. The ZTC drives each corresponding trim air modulating valve more open or more closed to force sensed zone temperature to agree with selected temperature.
(5)
Cargo Compartment
(a)
Cargo compartment temperature is selected with the MAIN DECK TEMP FWD, MAIN DECK TEMP AFT, LOWER LOBE TEMP FWD, and LOWER LOBE TEMP AFT selector knobs on the cabin temperature control module. The ZTC compares the selected temperature with the signals from the cargo compartment zone temperature sensors and duct temperature sensor. The ZTC drives the cargo compartment trim air modulating valve more open or more closed to force sensed zone temperature to agree with selected temperature.
(b)
If the ZTC fails to regulate cargo compartment temperature correctly, the cargo compartment trim air modulating valves may be placed under manual control. When the applicable TEMP knob (MAIN DECK or LOWER LOBE, FWD or AFT) is placed in the MAN position, the ZTC is bypassed. The selector may be held toward W to drive the trim air modulating valve more open, or held toward C to drive the valve more closed.
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ALL ú ú 01F Page 15 ú Oct 10/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL
(6)
The ZTC provides automatic temperature biasing to slowly increase zone temperatures to compensate for cabin humidity. The ECS miscellaneous card provides the ZTC with signals to indicate airplane altitude greater than 25K feet, cruise mode entered, and descent detected.
(7)
During ground operation on the APU, APU pneumatic output is regulated by a demand signal from the ZTC. If the air conditioning packs go into 75° F backup mode, APU flow output is set to maximum.
(8)
Flight Crew Indication
(a)
The EICAS ECS maintenance page displays zone temperature, target temperature, duct temperature, and trim air modulating valve position for each zone, and displays pressure in the trim air duct downstream of the master trim air shutoff valve. The EICAS ECS synoptic page displays target temperature and actual temperature for each zone.
(b)
The EICAS advisory message >TRIM AIR OFF is displayed when the master trim air shutoff valve is commanded closed. The advisory message TEMP ZONE is displayed if a duct overheat has occurred or if the ZTC fails. The status message ZONE TEMP is displayed to indicate a failure of a zone temperature control system LRU. The fault may be isolated to the specific LRU with the central maintenance computer system.
(c)
The status message CARGO ZONE TEMP is displayed to indicate a failure of a cargo zone temperature control LRU. The fault may be isolated to the specific LRU with the central maintenance computer system.
B. Control
(1)
To operate the zone temperature control system, the air conditioning packs must be activated. Refer to 21-00-00/201 for pack startup and shutdown. The TRIM AIR switch on the cabin temperature control module must be in the ON position.
(2)
The selected and the actual temperatures for each airplane zone and the master passenger compartment temperature setting may be viewed by selecting the EICAS ECS synoptic page.
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