S 865-015
(11)
Put the RECIRC FAN switch on the P5-10 air conditioning panel to AUTO.
(12)
Make sure the recirculation fan is operating.
(13)
Make sure the forward outflow valve closes fully.
S 735-016
S 735-017
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737-300/400/500MAINTENANCE MANUAL
E. Put the Airplane Back to Its Usual Condition
S 415-018
(1)
Install the lining in the forward cargo compartment that was removed to gain access to the forward outflow valve (AMM 25-52-73/401).
S 865-019
(2)
Remove electrical power if it is not necessary (AMM 24-22-00/201).
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A
737-300/400/500MAINTENANCE MANUAL
COOLING - DESCRIPTION AND OPERATION
___________________________________
1. General_______
A. The cooling system is divided into two subsystems. Section 21-51-00, Air Cycle System, discusses the path of the air being cooled and the equipment used for cooling it. Section 21-52-00, Ram Air System, describes the system, which employs outside air as a cooling medium for the air cycle system, and its control. See Figure 1 for location of cooling air and ram air equipment.
B. There are two air cycle systems on each airplane. The systems are virtually identical and are located on either side of the airplane centerline in a fairing beneath the center fuselage. The left system is considered to supply the control cabin and the right system the passenger cabin. The systems operate in parallel, however, and feed to a common manifold. During normal operation the control cabin utilizes only approximately twenty percent of the left system supply with the balance going to the passenger cabin. Either system operating alone is capable of maintaining acceptable temperature when necessary.
C. Cooling includes that portion of the air conditioning system which reduces the temperature of air received from the pneumatic system enough to meet any cooling requirement of the air conditioning system. The method of cooling this air consists of air-to-air type heat exchangers and an expansion turbine air cycle machine.
D. Air from the pneumatic system can be divided such that all or part of the air is passed through the cooling system with the remainder passing on to the mixing chamber. The cooled air is then mixed with the bypassed air to supply properly conditioned air to the distribution system. Two mix valves, one for each air cycle system, proportion the air.
E. The air cycle system supplies the cold air needed for mixture with the hot compressed engine bleed air to provide a selected temperature in the control and passenger cabins. Air from the Pneumatic System, Chapter 36, is received into the air conditioning system. The air must be cooled a variable amount depending upon environmental conditions of the cabin. The temperature of air entering the cabins is regulated by the two mix valves. These valves send part or all of the air through the air cycle system to be cooled and bypass the remainder to be mixed with the cold air in the mixing chamber. See Temperature Control, 21-61-00.
F. Since airflow through the air cycle system and hot air bypassing the system are supplied by the same duct, and airflow to the cabin is relatively constant , the mix valves regulate the quantity of cold air being supplied and also influence the temperature drop across the air cycle system. A water separator 35°F control system bypasses warm air around the turbine to mix with cold air from the turbine to prevent freezing in the water separator. As a result, cold air at the water separator is never below freezing.
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