21-CONTENTS
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ú GUN.101 Page 19
ú Sep 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757 MAINTENANCE MANUAL
AIR CONDITIONING - GENERAL - DESCRIPTION AND OPERATION
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1. General (Fig. 1)_______
A. The air conditioning system maintains airplane environmental control for the comfort of passengers and crew. The total system is made up of the conditioned air distribution system, pressurization control system, cargo compartment heating system, cooling system and temperature control system.
B. Distribution
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(1)
The distribution system channels temperature-controlled air to the flight deck and passenger cabin through a network of distribution ducts. The main mix manifold (AMM 21-21-00/001) combines cooled air from the air cooling packs (AMM 21-51-00/001) with recirculation air (AMM 21-25-00/001) drawn from the passenger cabin. The air is channeled to the flight deck through ducts (AMM 21-22-00/001) and to the passenger compartment through risers, overhead ducting and outlets (AMM 21-23-00/001). Separate exhaust ducting provides positive ventilation for all lavatory and galley areas (AMM 21-26-00/001).
C.
Pressurization Control
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(1)
The air conditioning system provides pressurization control by regulating the amount of air discharged from the airplane (Ref 21-31-00). Backup positive and negative pressurization relief systems prevent the cabin pressure from exceeding established limits (Ref 21-32-00). Pressurization indication and warning systems (Ref 21-33-00) allow the operator to monitor the pressurization control system.
D.
Heating
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(1)
Independent cargo compartment heating systems provide temperature control for the forward (Ref 21-43-00), aft and bulk (Ref 21-44-00) cargo compartments.
(2)
The supplemental heating system channels heated air to the captain's and first officer's foot and shoulder areas (Ref 21-45-00).
E.
Cooling
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(1)
Cooled air is supplied to the distribution system by two air cooling packs (AMM 21-51-00/001). The pneumatic system (AMM 36-00-00/001) provides source air to the packs. The ram air system (AMM 21-53-00 /001) assures pack temperature control. The pack indicating system allows flight deck monitoring of pack operation (AMM 21-52-00/001).
(2)
The equipment cooling system removes heat generated by electrical and electronic equipment in the flight compartment, forward equipment area, main equipment racks (Ref 21-58-00), and aft equipment area (Ref 21-26-00).
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ALL ú ú 01 Page 1 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
SYSTEMS
Environmental Control Systems
Figure 1
A
757
MAINTENANCE MANUAL
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21-00-00
ALL ú ú 01 Page 2 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
F. Temperature Control
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(1)
The temperature control system regulates the environment within the airplane's three primary zones (AMM 21-61-00/001). Cooled air mixes with hot "trim" air to obtain the desired temperature at each zone. Monitoring of the system is provided by valve position indication (AMM 21-64-00/001) and the zone temperature indication system (AMM 21-65-00/001).
G.
Control and Indication (Fig. 2)
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(1)
Control selectors and switchlights, on the pilot's overhead panel P5, and one control selector on the right side panel P61 allow control of all air conditioning systems. Warning lights, position indicators and other gages on the P5 panel provide partial indication of system operation. The Engine Indication and Crew Alerting System (EICAS) (AMM 31-41-00) provides the remaining indication for the air conditioning system.
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