C. The equipment cooling system has several items that 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.
519
Nov 1/74 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-58-0 Page 101
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 actuates the warning light to on anytime there is not enough airflow or failure of air movement in the system.
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.
NOTE: Prior to using trouble shooting charts check press-to-test OFF light and on Passenger/Cargo Convertible airplanes, check that smoke clearance switch is in NORMAL position.
F. Trouble Shooting Charts
(1) The following chart is for normal blower operation, ie with blower selector switch at NORMAL. If problem was encountered with switch at ALTERNATE, substitute alternate blower and alternate blower relay and reverse check valves positions where applicable. For switch continuity in alternate position check between contacts 4 and 5.
T51713
501
21-58-0 Page 102 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/01
T51716
501
Aug 15/76 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-58-0 Page 103
EQUIPMENT COOLING SYSTEM - BALANCING
1. General
A. No balancing of the heat loads is necessary except for shelves E3-1 and E3-3.
B. For shelves E3-1 or E3-3 proceed as follows:
(1)
If new item of equipment needs lesser cooling than old item, do not balance system.
(2)
If new item of equipment needs more cooling than old item, balance shelf.
(a) E3 shelves are designed for a flow of 60 cfm each.
2. Balance Shelves E3-1 and E3-3
A. Provide enough orifice air inlet area for each shelf so as to obtain the correct airflow in cfm. Airflow for different size orifices is given in figure 201.
B. Measure shelf negative pressure with a static pressure probe and a manometer of a range of between 0 and 5 inches of water. Measurement must be made with system operating.
500
Feb 15/68 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-58-0 Page 201
Rack Airflow per Orifice 500
21-58-0 Figure 201 Feb 15/68
Page 202
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
1. General
A. For maintenance activities requiring main electrical power on for more than 20 minutes at outside ambient temperature greater than 100°F (37.8°C), it is recommended that conditioned air be supplied to the cabin. This will improve the thermal environment for the electrical equipment.
B. The electronic racks provide the proper airflow for each shelf to properly cool the equipment for which the rack was designed and a balanced airflow is attained by the use of fixed orifice plates. If equipment is not installed in the airplane at delivery, the orifices in these empty trays are covered with a metering plate or tape. The metering plates or tape must be removed prior to installing equipment to prevent the equipment from overheating.
C. When equipment for which the racks are designed is rearranged or modified, thereby changing the heat loads, it will be necessary to rebalance the system. Extra space on racks could be used for adding equipment. If extra equipment is added, the other orifices may no longer provide a balanced airflow for their equipment and overheating could occur. Before adding extra equipment engineering must check and resize orifices as necessary to provide proper cooling. Figure 501 shows the location of equipment cooling racks.
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