AIR CONDITIONING

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航空

AIR CONDITIONING - DESCRIPTION AND OPERATION
1. General
A. The air conditioning systems provide conditioned air to the control cabin, passenger cabin,
electronic equipment compartment, forward cargo compartment, air conditioning distribution
bay and aft cargo compartment. Air supply to the air conditioning system is furnished by the
pneumatic system from either engine bleed air or the auxiliary power unit (APU) in flight, and
from engine bleed air, the auxiliary power unit, a ground pneumatic supply cart, or from a
ground conditioned air supply cart during ground operation (Fig. 1). Chapter 36, Pneumatic,
describes air supply to the pneumatic manifold. Part of the warm air supply from the engines or
pneumatic cart is passed through the air cycle system to be cooled. The cold air is then mixed
with the remainder of the warm air as required to obtain the conditioned air temperature called
for by the temperature control system. This conditioned air then passes into the control and
passenger cabins through the distribution system. Cabin air is exhausted a number of ways.
Galley and toilet vents, the ground service air conditioning connection check valve, condensate
drains, and the water separator drains, for example, exhaust cabin air without regard for cabin
pressurization control requirements. The combined flow from all outlets other than the
pressurization control outflow valves is limited to a value less than that which enters the cabin
from the air conditioning system. The outflow valves are regulated to exhaust only that
additional quantity of air required to maintain the desired pressure in the cabin. For a more
detailed description of the electrical/electronic equipment cooling, refer to Equipment Cooling
System - Description and Operation.
B. This chapter considers the air conditioning system as including five subsystems: compression,
distribution, pressurization control, cooling, and temperature control. Figure 2 shows the flow of
air through the airplane for air conditioning and pressurization.
2. Compression
A. This subsystem describes the equipment and methods used to regulate flow of air to the air
conditioning system. Regulated flow is required to maintain adequate air supply and to prevent
excessive flow. Undersupply may limit pressurization of the airplane, while over supply may
cause the air cycle system to overheat.

B. The engines furnish 8th- or 13th-stage air, depending on engine power setting and air
conditioning demand, for air conditioning during normal operation. Bleed air from the engines
enters the pneumatic system, where the temperature is normally regulated to approximately
370°F and limited to 450°F. A thermoswitch in the pneumatic system will prevent excessively
hot air from entering the air conditioning system by closing the bleed air shutoff valve. Airflow to
each air conditioning system is initiated by a pack valve which includes features for regulating
airflow. The compression subsystem explains how airflow is controlled.
C. An air cleaner system is provided to purge the engine bleed air of impurities. The system
consists of two similar subsystems which function automatically whenever engine bleed air is
used for air conditioning, and the airplane is on the ground or the flaps are extended. Each
subsystem consists of an inertial type air cleaner and purge line, an electrically controlled
pneumatically operated purge valve and an electrical control system. The impurities collected
by the cleaner are vented overboard through the ram air exhaust louvers. For a more detailed
description of the air cleaner system, refer to Air Cleaner System - Description and Operation.
3. Distribution
A. Two separate and independent systems distribute air to the passenger and control cabins. The
individual (gasper) air distribution system routes only the cold air from the air cycle system
while the conditioned air distribution system routes a mixture of the cold and hot air to the
cabins.
B. The gasper system provides each crewmember and passenger a method for cooling his local
area to a value different from that provided by normal air conditioning automatic control. Air is
received from the air cycle system and ducted to each individual station. An adjustable nozzle
at each station allows the individual a choice anywhere between no supplementary cold air and
full system capacity cold air. With all gasper outlets open approximately 20% (maximum) of the
total cabin inflow air passes through the gasper system.
C. The conditioned air distribution system routes temperature controlled air to the passenger and
control cabins. One duct system supplies the control cabin and another entirely separate duct
system supplies the passenger cabin. Both systems originate at the main distribution manifold
with ducts extending forward. Riser ducts near the forward end of the passenger cabin connect
to an overhead duct extending fore and aft the full length of the passenger cabin. A nozzle at
the bottom of the duct releases a balanced flow of air directly into the cabin.
4. Pressurization Control System
A. The pressurization control system includes pressurization control, pressurization relief valves,
and pressurization indicating and warning.

B. Cabin pressure is controlled by positioning a cabin pressurization outflow valve to meter cabin
air exhaust. The valve operates electrically from any of three different control systems. Two of
these control systems, AUTO and STANDBY, are electronic and provide automatic pressure
control, while the third, MANUAL, requires manual switch operation for adjustment. Normal
control is from the AUTO system with the STANDBY system acting as a backup. The MANUAL
system functions as an override over both automatic systems.
C. Pressurization relief valves include two safety relief valves, which prevent overpressurizing the
airplane, and a vacuum relief valve which prevents pressure inside the airplane becoming
appreciably less than ambient. In addition to the relief valves, pressure equalization valves are
installed in both cargo compartments to provide a quick method of allowing cargo compartment
pressure to vary, within limits, with cabin pressure. Blowout panels are used in both cargo
compartments to protect against a sudden differential in pressure between the cargo
compartment interior and exterior.
D. Indicators are provided to allow monitoring cabin altitude, differential pressure, and rate of
pressure change. A cabin altitude warning system sounds a horn if cabin altitude exceeds
approximately 10,000 feet.
5. Cooling
A. All cold air required for air conditioning is provided by an air cycle system. Passing bleed air
through a primary heat exchanger, an air cycle machine, and a secondary heat exchanger
cools the air sufficiently to handle any cooling situation required. A ram air system provides
coolant air for the heat exchangers. A ram air modulation control system automatically
regulates the supply of coolant air during flight to obtain required cooling with minimum
aerodynamic drag from the system. A turbofan draws air through the system for ground
operation. A water separator removes excess moisture from the cooled air. Various thermal
switches, thermostats, sensors, and valves are included with the system to provide automatic
protection and warning of an air cycle system malfunction.
6. Temperature Control
A. Temperature of the air entering the distribution systems to the passenger and control cabins is
regulated by positioning mix valves. The mix valves proportion hot bleed air with cold air from
the air cycle system to provide air conditioned comfort in the passenger and control cabin.
There is one mix valve for each air cycle system. Two sets of controls on the forward overhead
panel provide automatic or manual control and system monitoring for each system. The control
cabin controls apply to the left air cycle system and the passenger cabin controls the right air
cycle system. Each control system consists of a temperature regulator, temperature indicator,
temperature sensors, overheat control and warning light, mix valve, and mix valve position
indicator.

AIR CONDITIONING - MAINTENANCE PRACTICES
1. Pack Cooling System Performance Test
A. General
(1) The following procedure is developed for detection of system abnormalities using only
airplane instrumentation. This procedure is intended to provide quick evaluation of system
performance for scheduled maintenance checks and trouble shoot flight operation
problems.
B. Reference Procedures
(1) 49-11-0, APU Power Plant Operating Procedure
C. Prepare for Air Conditioning Test
(1) Check that all air conditioning and pneumatic circuit breakers are closed (in).
(2) Check that the following circuit breakers on circuit breaker panel P6 are closed:
(a) MASTER CAUTION (all except FUEL, if installed)
(b) INDICATOR LIGHTS, MASTER DIM BUS (9 places)
(c) DIM & TEST (1 place)
(3) Check warning lights and annunciators.
(a) Place LIGHTS switch on lightshield panel (P2-l) to TEST. Check that both MASTER
CAUTION lights, the AIR COND annunciator light and PACK TRIP OFF light come
on.
(4) Open air conditioning equipment bay door.

(5) Operate both cabin temperature selectors on overhead panel to place mix valves in full
cold position and leave both selectors in OFF MANUAL position. Check that both visual
indicators on air mix valves in air conditioning bay, show full cold position. If not, repair
temperature control system before proceeding (Ref 21-61-0, Conditioned Air Temperature
Control Systems).
(6) Place engine 1 and 2 BLEED switches on overhead panel to OFF position and APU
BLEED switch to ON position.
(7) Provide APU power (Ref 49-11-0).
NOTE: Electrical load to be less than 25 amperes.
(8) Place both air conditioning (A/C) PACK switches to OFF position.
(9) Place ISOLATION VALVE switch to OPEN position.
(10) Record ambient temperature which is used for calculation in flow and heat exchanger
check.
(11) Record APU exhaust gas temperature (EGT).
NOTE: This is used for calculation in flow check. Allow time for EGT to stabilize and tap
indicator to remove hysteresis. Ensure valve positions, remain as stated, to avoid
effect of leakage variance.
D. Test air conditioning system.
(1) Turbofan Valve Test
(a) Remove both connectors from turbofan valve solenoids and manually override the
valve opens. Check that the valve modulates to a position somewhere less than full
open.
NOTE: Duct pressure should be higher than the valve maximum regulating
pressure of 33 psi. A valve that is fully open is regulating too high.
(b) Replace the connectors and turn both packs ON. Observe that the valves are full
open.
NOTE: Duct pressure will be lower than the valve minimum regulating pressure of
27 psi. A valve that is not fully open is regulating too low.
(2) Flow and Primary Heat Exchanger Test
(a) With both A/C packs ON, note APU EGT.
NOTE: EGT should be within established maximum limits to ensure adequate flow
for these tests.

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AIR CONDITIONING