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 B.  In each pack the pneumatic bleed air supply is metered through a flow control and shutoff valve and is cooled in a heat exchanger. The air is further cooled by a bootstrap air cycle machine (ACM) as required by the pack temperature control system (AMM 21-62-00/001). The cooled air is passed through a water separator into a discharge duct leading to the conditioned air plenum chamber (AMM 21-21-00/001).
 C.  Ram air is the cooling medium in the heat exchanger during flight. During operation on the ground, a fan on the air cycle machine moves air through the heat exchanger while a check valve prevents backflow of air through the ram air inlet. Air flow through the ram air system is controlled by the pack temperature control system (Ref 21-62-00/001). Moisture removed from the conditioned air by the water separator is collected and is piped to an aspirator which sprays water into the ram air side of the heat exchanger to provide additional cooling through evaporation.
 D.  Electrical power and a source of pneumatic air are required to operate the packs. A minimum pressure shutoff control on the flow control and shutoff valve will cause the valve to be closed if pneumatic manifold pressure drops below 8-12 psi. This is a priority feature that reserves available air for pneumatic flight controls.
 E.  Catalytic (ozone) converters are installed in the bleed air supply ducts just upstream of each flow control and shutoff valve to minimize the entry of ozone into the airplane.
 2.  Flow Control and Shutoff Valve (Fig. 2)______________________________
 A.  The flow of pneumatic bleed air through each air conditioning pack is controlled by a flow control and shutoff valve which provides a nearly constant volumetric flow of air to the pack. The flow control and shutoff valve assembly contains a 6-1/2 inch diameter butterfly valve, a dual piston pneumatic actuator, a diaphragm-operated pneumatic servo control, and a control valve flow sensor mounted on a venturi upstream of the butterfly. The assembly also includes a shutoff solenoid, a normal flow solenoid, and a valve closed limit switch.
 B.  When the shutoff solenoid is energized, the valve is driven closed, deactivating the air conditioning pack. The shutoff solenoid is controlled manually from the flight deck with the pack selector switch on the bleed air control module and automatically by the pack temperature controller and the pack overheat and out-of sequence airplane wiring logic.
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 21-51-00
 ALL  ú ú 01F Page 1 ú Oct 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 747-400 MAINTENANCE MANUAL
TO ZONES

CONNECTORS (REF)
APU BLEED AIR (REF)
AIR CONDITIONING PACKS BLOCK DIAGRAM
TO CONDITIONED AIR
DUAL HEAT
NOTE: SMACCS IS SMOKE MODE AIR
PLENUM CHAMBER
EXCHANGER

COMPRESSOR TURBINE
AIR CONDITIONING PACK FLOW DIAGRAM (EXAMPLE)
Air Conditioning Packs Diagrams
Figure 1

C23311
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 21-51-00
 ALL  ú
 ú  01F  Page 2
 ú  Feb 10/95 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400 MAINTENANCE MANUAL
SEE A
PACK TEMPERATURE CONTROLLERS
ECS MISCELLANEOUS AND FREIGHTER CIRCUIT
FAN FLT TEMPFWD MAIN AFT
CARDS IN M7603 CARD FILE
DECK AUTO AUTO  DECK AUTO TEMP
ON CW
MAN
CW CW
MAN MAN CABIN TEMPERATURE
FWD LOWER AFTCONTROL MODULE ZONE RST TRIM AIR
AUTO LOBE AUTO TEMP ON
SYS FAULTa
CW CW EQUIP COOLING
MAN MAN
NORM
HI FLOW PACK RST  AFT CARGO HT STBY
OVRD
ON ON
SYS TEMPFAULTa a
1 PACKS 2 PACKS 3
NORM NORM NORM OFF
A B
A OFF A OFF
B B
L ISLN R ISLN
BLEED AIR
VALVE VALVE
a a
CONTROL
MODULE
w w
WING
WING TAI TAI APU
SYS SYS
SYS SYSON
w
FAULT a FAULT a
FAULT a FAULT a
VALVE
a
1 2 3 4
ON ON ON ON
w
w
ENGINE
w w
BLEED
OFF OFF OFF OFF
a
a a a
PILOTS' OVERHEAD PANEL A Air Conditioning Pack System - Component Location Figure 2 (Sheet 1)
　
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