Right Air Cycle System Airflow Diagram  532 
21-51-0  (Left Air Cycle System Similar)  Nov 15/71 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

COOLING - TROUBLE SHOOTING
1. General
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° control sensor, 35° control valve and 35° control are functionally related. Another grouping includes the heat exchangers; air cycle machine, ram air system, and the compressor discharge and turbine inlet overheat thermal switches.
2.  Water Separator - 35° Control
A.  Trouble in the water separator, 35° control system may be recognized by moisture or fog in the cabin, a pounding noise from the 35° control valve opening and closing, or by the lack of water emerging from the water separator drain during air conditioning operation when on the ground. Water separator problems may be caused by water freezing on the condenser bag as a result of a faulty 35° sensor or 35° control valve, or 35° control, or a dirty condenser bag.
B.  Built-in test equipment on some 35° controls provide a method for checking electrical operation of 35° control system and if there are problems will isolate the faulty component. Test instructions are printed on the control unit.
3.  Cooling Equipment
A.  Thermal switches are located in the system to prevent overheat damage to other cooling system equipment. Sensors, trouble lights, and 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 or the ACM turbine inlet overheat switch actuation will cause pack shutdown.
B.  When either overheat switch closes a circuit is completed to close the respective pack valve. Should a system trip off it may be that proper cooling is not being accomplished by the secondary heat exchanger and trip-off results from the turbine inlet overheat switch.
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C.  For turbine inlet overheat trip-off, remove inspection door on underside of ram air duct forward of secondary heat exchanger and examine for any obstruction to flow at end of the secondary heat exchanger. If no obstruction, check turbine inlet overheat switch.
D.  System trip-off from overheat may result from any one of several failures. In each case indicator readings may give a clue as to where the malfunction exists. System overheat will result either from restriction of airflow through the ram air system, an over abundance of air supply from the pneumatic system, or an inoperative mix valve which permits passage of hot engine bleed air only. Should air supply to the ACM be greater than normal, system temperature will rise although not necessarily enough to cause the system to trip off. The increase in flow will cause a corresponding increase through air conditioning ducts which may be reported as abnormal duct noise and/or low engine pressure ratio indicator reading. If the 13th-stage high pressure modulating valve fails in the full open position, system may trip off due to overheat. At such time the increase in airflow to the cabin will be so great that it cannot escape notice. For trouble shooting the modulating valve and engine bleed air compression control system, refer to 21-11-0.
4.  Wing and Lower Aft Body Overheat Detection
A.  When operating air cycle system on auxiliary power unit (APU) air during hot weather the air cycle system and/or pneumatic hot air ducts could cause nuisance trips of the Wing and Lower Aft Body Overheat Detection System, 26-18-0. Should overheat detection system trip without excessive duct leakage, check cleanliness of ducts (Ref 36-19-11, Maintenance Practices).
5.  Trouble Shooting Chart
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E61524 E62049 E61987 E62027
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