AIR CONDITIONING
**** Hidden Message ***** <P>AIR CONDITIONING - DESCRIPTION AND OPERATION<BR>1. General<BR>A. The air conditioning systems provide conditioned air to the control cabin, passenger cabin,<BR>electronic equipment compartment, forward cargo compartment, air conditioning distribution<BR>bay and aft cargo compartment. Air supply to the air conditioning system is furnished by the<BR>pneumatic system from either engine bleed air or the auxiliary power unit (APU) in flight, and<BR>from engine bleed air, the auxiliary power unit, a ground pneumatic supply cart, or from a<BR>ground conditioned air supply cart during ground operation (Fig. 1). Chapter 36, Pneumatic,<BR>describes air supply to the pneumatic manifold. Part of the warm air supply from the engines or<BR>pneumatic cart is passed through the air cycle system to be cooled. The cold air is then mixed<BR>with the remainder of the warm air as required to obtain the conditioned air temperature called<BR>for by the temperature control system. This conditioned air then passes into the control and<BR>passenger cabins through the distribution system. Cabin air is exhausted a number of ways.<BR>Galley and toilet vents, the ground service air conditioning connection check valve, condensate<BR>drains, and the water separator drains, for example, exhaust cabin air without regard for cabin<BR>pressurization control requirements. The combined flow from all outlets other than the<BR>pressurization control outflow valves is limited to a value less than that which enters the cabin<BR>from the air conditioning system. The outflow valves are regulated to exhaust only that<BR>additional quantity of air required to maintain the desired pressure in the cabin. For a more<BR>detailed description of the electrical/electronic equipment cooling, refer to Equipment Cooling<BR>System - Description and Operation.<BR>B. This chapter considers the air conditioning system as including five subsystems: compression,<BR>distribution, pressurization control, cooling, and temperature control. Figure 2 shows the flow of<BR>air through the airplane for air conditioning and pressurization.<BR>2. Compression<BR>A. This subsystem describes the equipment and methods used to regulate flow of air to the air<BR>conditioning system. Regulated flow is required to maintain adequate air supply and to prevent<BR>excessive flow. Undersupply may limit pressurization of the airplane, while over supply may<BR>cause the air cycle system to overheat.</P><P>B. The engines furnish 8th- or 13th-stage air, depending on engine power setting and air<BR>conditioning demand, for air conditioning during normal operation. Bleed air from the engines<BR>enters the pneumatic system, where the temperature is normally regulated to approximately<BR>370°F and limited to 450°F. A thermoswitch in the pneumatic system will prevent excessively<BR>hot air from entering the air conditioning system by closing the bleed air shutoff valve. Airflow to<BR>each air conditioning system is initiated by a pack valve which includes features for regulating<BR>airflow. The compression subsystem explains how airflow is controlled.<BR>C. An air cleaner system is provided to purge the engine bleed air of impurities. The system<BR>consists of two similar subsystems which function automatically whenever engine bleed air is<BR>used for air conditioning, and the airplane is on the ground or the flaps are extended. Each<BR>subsystem consists of an inertial type air cleaner and purge line, an electrically controlled<BR>pneumatically operated purge valve and an electrical control system. The impurities collected<BR>by the cleaner are vented overboard through the ram air exhaust louvers. For a more detailed<BR>description of the air cleaner system, refer to Air Cleaner System - Description and Operation.<BR>3. Distribution<BR>A. Two separate and independent systems distribute air to the passenger and control cabins. The<BR>individual (gasper) air distribution system routes only the cold air from the air cycle system<BR>while the conditioned air distribution system routes a mixture of the cold and hot air to the<BR>cabins.<BR>B. The gasper system provides each crewmember and passenger a method for cooling his local<BR>area to a value different from that provided by normal air conditioning automatic control. Air is<BR>received from the air cycle system and ducted to each individual station. An adjustable nozzle<BR>at each station allows the individual a choice anywhere between no supplementary cold air and<BR>full system capacity cold air. With all gasper outlets open approximately 20% (maximum) of the<BR>total cabin inflow air passes through the gasper system.<BR>C. The conditioned air distribution system routes temperature controlled air to the passenger and<BR>control cabins. One duct system supplies the control cabin and another entirely separate duct<BR>system supplies the passenger cabin. Both systems originate at the main distribution manifold<BR>with ducts extending forward. Riser ducts near the forward end of the passenger cabin connect<BR>to an overhead duct extending fore and aft the full length of the passenger cabin. A nozzle at<BR>the bottom of the duct releases a balanced flow of air directly into the cabin.<BR>4. Pressurization Control System<BR>A. The pressurization control system includes pressurization control, pressurization relief valves,<BR>and pressurization indicating and warning.</P>
<P>B. Cabin pressure is controlled by positioning a cabin pressurization outflow valve to meter cabin<BR>air exhaust. The valve operates electrically from any of three different control systems. Two of<BR>these control systems, AUTO and STANDBY, are electronic and provide automatic pressure<BR>control, while the third, MANUAL, requires manual switch operation for adjustment. Normal<BR>control is from the AUTO system with the STANDBY system acting as a backup. The MANUAL<BR>system functions as an override over both automatic systems.<BR>C. Pressurization relief valves include two safety relief valves, which prevent overpressurizing the<BR>airplane, and a vacuum relief valve which prevents pressure inside the airplane becoming<BR>appreciably less than ambient. In addition to the relief valves, pressure equalization valves are<BR>installed in both cargo compartments to provide a quick method of allowing cargo compartment<BR>pressure to vary, within limits, with cabin pressure. Blowout panels are used in both cargo<BR>compartments to protect against a sudden differential in pressure between the cargo<BR>compartment interior and exterior.<BR>D. Indicators are provided to allow monitoring cabin altitude, differential pressure, and rate of<BR>pressure change. A cabin altitude warning system sounds a horn if cabin altitude exceeds<BR>approximately 10,000 feet.<BR>5. Cooling<BR>A. All cold air required for air conditioning is provided by an air cycle system. Passing bleed air<BR>through a primary heat exchanger, an air cycle machine, and a secondary heat exchanger<BR>cools the air sufficiently to handle any cooling situation required. A ram air system provides<BR>coolant air for the heat exchangers. A ram air modulation control system automatically<BR>regulates the supply of coolant air during flight to obtain required cooling with minimum<BR>aerodynamic drag from the system. A turbofan draws air through the system for ground<BR>operation. A water separator removes excess moisture from the cooled air. Various thermal<BR>switches, thermostats, sensors, and valves are included with the system to provide automatic<BR>protection and warning of an air cycle system malfunction.<BR>6. Temperature Control<BR>A. Temperature of the air entering the distribution systems to the passenger and control cabins is<BR>regulated by positioning mix valves. The mix valves proportion hot bleed air with cold air from<BR>the air cycle system to provide air conditioned comfort in the passenger and control cabin.<BR>There is one mix valve for each air cycle system. Two sets of controls on the forward overhead<BR>panel provide automatic or manual control and system monitoring for each system. The control<BR>cabin controls apply to the left air cycle system and the passenger cabin controls the right air<BR>cycle system. Each control system consists of a temperature regulator, temperature indicator,<BR>temperature sensors, overheat control and warning light, mix valve, and mix valve position<BR>indicator.</P>
<P>AIR CONDITIONING - MAINTENANCE PRACTICES<BR>1. Pack Cooling System Performance Test<BR>A. General<BR>(1) The following procedure is developed for detection of system abnormalities using only<BR>airplane instrumentation. This procedure is intended to provide quick evaluation of system<BR>performance for scheduled maintenance checks and trouble shoot flight operation<BR>problems.<BR>B. Reference Procedures<BR>(1) 49-11-0, APU Power Plant Operating Procedure<BR>C. Prepare for Air Conditioning Test<BR>(1) Check that all air conditioning and pneumatic circuit breakers are closed (in).<BR>(2) Check that the following circuit breakers on circuit breaker panel P6 are closed:<BR>(a) MASTER CAUTION (all except FUEL, if installed)<BR>(b) INDICATOR LIGHTS, MASTER DIM BUS (9 places)<BR>(c) DIM & TEST (1 place)<BR>(3) Check warning lights and annunciators.<BR>(a) Place LIGHTS switch on lightshield panel (P2-l) to TEST. Check that both MASTER<BR>CAUTION lights, the AIR COND annunciator light and PACK TRIP OFF light come<BR>on.<BR>(4) Open air conditioning equipment bay door.</P>
<P>(5) Operate both cabin temperature selectors on overhead panel to place mix valves in full<BR>cold position and leave both selectors in OFF MANUAL position. Check that both visual<BR>indicators on air mix valves in air conditioning bay, show full cold position. If not, repair<BR>temperature control system before proceeding (Ref 21-61-0, Conditioned Air Temperature<BR>Control Systems).<BR>(6) Place engine 1 and 2 BLEED switches on overhead panel to OFF position and APU<BR>BLEED switch to ON position.<BR>(7) Provide APU power (Ref 49-11-0).<BR>NOTE: Electrical load to be less than 25 amperes.<BR>(8) Place both air conditioning (A/C) PACK switches to OFF position.<BR>(9) Place ISOLATION VALVE switch to OPEN position.<BR>(10) Record ambient temperature which is used for calculation in flow and heat exchanger<BR>check.<BR>(11) Record APU exhaust gas temperature (EGT).<BR>NOTE: This is used for calculation in flow check. Allow time for EGT to stabilize and tap<BR>indicator to remove hysteresis. Ensure valve positions, remain as stated, to avoid<BR>effect of leakage variance.<BR>D. Test air conditioning system.<BR>(1) Turbofan Valve Test<BR>(a) Remove both connectors from turbofan valve solenoids and manually override the<BR>valve opens. Check that the valve modulates to a position somewhere less than full<BR>open.<BR>NOTE: Duct pressure should be higher than the valve maximum regulating<BR>pressure of 33 psi. A valve that is fully open is regulating too high.<BR>(b) Replace the connectors and turn both packs ON. Observe that the valves are full<BR>open.<BR>NOTE: Duct pressure will be lower than the valve minimum regulating pressure of<BR>27 psi. A valve that is not fully open is regulating too low.<BR>(2) Flow and Primary Heat Exchanger Test<BR>(a) With both A/C packs ON, note APU EGT.<BR>NOTE: EGT should be within established maximum limits to ensure adequate flow<BR>for these tests.</P> AIR CONDITIONING
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