(2)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-7; When the differential pressure reaches .7 to 1.1 the valve is closed. While the pressure differential is greater than .7 to 1.1 psi, the equipment cooling air will exhaust mainly to the forward cargo compartment.
C. During normal operation the airflow through the equipment cooling system is sufficient to remove heat from the detector heater, preventing the temperature sensitive switch from activating. When the airflow through the system is not sufficient to remove heat from the heater, the temperature around the switch rises, actuating the switch. This illuminates the OFF warning light. The OFF warning light on the overhead panel will remain on until airflow through the system is sufficient to remove heat from the heater.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITHOUT EFIS ú
21-58-00
ú ú 06 Page 5 ú Jul 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
EQUIPMENT COOLING SYSTEM - TROUBLE SHOOTING
___________________________________________
1. General
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A. In trouble shooting the equipment cooling system two cooling problems may exist. One concerns the equipment in the racks and sizing of the orifice openings. The other will result from faulty components in the air moving portion of the system.
CAUTION: IF ORIFICE OPENINGS ARE IMPROPERLY ADJUSTED, EQUIPMENT ON THE
_______ RACKS MAY OVERHEAT. DO NOT ADD EQUIPMENT OR CHANGE ADJUSTMENTS WITHOUT YOUR ENGINEERING DEPARTMENT APPROVAL.
B. Fixed orifice openings are provided to allow proper airflow for all equipment installed in the airplane. If orifices are not set properly or if additional orifices are added to provide cooling for equipment installed after delivery, it may upset the cooling balance and allow overheating of some electrical/electronic equipment. For a more detailed description of orifices, refer to 21-58-00, Adjustment/Test.
(1)
Cooling of equipment utilizes control cabin exhaust air. This air, drawn through the equipment, may contain impurities such as tars and nicotine which may settle on the equipment. If equipment is not cleaned for a considerable period of time, these deposits could adversely affect their cooling.
(2)
A performance test is provided in Equipment Cooling System -Adjustment/Test to check that airflow through the system is at or above specified minimum acceptable pressures. The trouble shooting procedure will isolate any fault which might cause the cooling system performance to deteriorate.
C. The equipment cooling system has several items which could cause trouble. They are the airflow detector, blowers, automatic flow control valve, and blower relays. When trouble shooting the equipment cooling system, always check that the blower is operating. Check by feel at the blower discharge port on the exterior of the airplane. If there is no airflow at the blower discharge port and the OFF amber warning light is on, check the flow limiting nozzle. If there is airflow at the flow limiting nozzle, the flow control valve is stuck shut and must be replaced. If the OFF amber warning light is on and there is airflow at the discharge port or the blower is not operating, trouble shoot per trouble shooting charts.
D. Failure of air movement in the equipment cooling system is indicated when the OFF amber warning light on the forward overhead panel illuminates. The OFF light is actuated by the temperature sensitive switch, a heated unit in the airflow detector system. It illuminates warning light anytime there is not enough airflow in the system.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITHOUT EFIS ú
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ú ú 02 Page 101 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
E. Few components of the equipment cooling system could cause failure of air movement in the system. The following trouble shooting charts are provided to isolate faulty components of the control and indicating system. If after using the trouble shooting charts the problem is not corrected, the trouble may be either in the electrical wiring or connectors. Refer to wiring diagram.
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