21-51-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
E. From the air cycle machine the air is ducted forward to the water separator. Excess moisture condenses from the air at the reduced temperature and is separated from the air and either sprayed into the ram air inlet or drained overboard. The water separator 35°F control system bypasses primary heat exchanger air around the air cycle machine, if needed, to prevent water freezing in the separator.
F. Cold air leaving the water separator then travels to the mixing chamber.
G. When the air conditioning switches are turned off, the pack valves close and the mix valve drive to full cold.
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21-51-00
ALL ú ú 01 Page 12 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
AIR CYCLE SYSTEM - TROUBLE SHOOTING
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General
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A. Trouble shooting the cooling portion of the air conditioning system involves both the air cycle system and the ram air system. An understanding of how the different components are interrelated as well as the function of each is needed to locate and correct problems in either system.
B. Grouping individual components according to function aids in locating a defective component. The water separator, 35°F control sensor, 35°F control valve and 35°F controller are functionally related. Another grouping includes the heat exchangers, air cycle machine, ram air system, the compressor discharge and turbine inlet overheat thermal switches and the pack temperature bulb.
Water Separator - 35°F Control
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A. Trouble in the water separator, 35°F control system may be recognized by moisture or fog in the cabin, a pounding noise from the 35°F water separator relief valve opening and closing, or by excessive water emerging from the water separator drain during air conditioning operation when on the ground (indicating plugged water spray injector). Water separator problems may be caused by water freezing on the coalescer bag as a result of a faulty 35°F sensor or 35°F control valve, or 35°F controller, or a dirty coalescer bag.
B. Built-in test equipment on 35°F controllers provides a method for checking the 35°F control system and if there are problems, will isolate the faulty component. Test instructions are printed on the control unit. The BITE test can also be found in the adjustment/test procedures (AMM 21-51-00/501).
Cooling Equipment
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A. Thermal switches are located in the system to prevent overheat damage to the cooling system. Warning lights and temperature indicators are provided to indicate abnormal conditions. When trouble shooting, it is helpful to consider the indicator reading at time of malfunction to locate faulty component. For example, either the air cycle machine (ACM) compressor discharge overheat switch, the ACM turbine inlet overheat switch or duct overheat switch actuation will cause pack trip-off.
B. Pack trip-offs may result from one of several failures in the air conditioning pack. The general causes of pack trip are as follows:
(1)
Thermal switch calibration set point on 390°F, 250°F, or 210°F thermal switches has drifted down to a lower set point.
(2)
Electrical malfunction which causes the pack trip relay to energize to trip position.
(3)
Pack valve butterfly failed to the open position or to a higher than normal flow position.
(4)
Ram air modulation system malfunction where system does not modulate open as required or there is blocked ducting or blocked heat exchanger passages.
(5)
Temperature control system malfunction where mix valve is driven to full hot position or the duct limit sensor, anticipator or cabin sensor malfunction.
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