2.0 to 2.8 psi.
(2)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-7; The selected blower operates continuously and the flow control valve is in the open position when the differential pressure is less than .7 to 1.1 psi.
B. When electrical power is connected to the airplane, circuit breaker panel P18-3 is energized and the blower and the low airflow sensor are energized. While the cabin pressure differential is low the blower creates the airflow necessary for cooling. In flight, cabin pressure differential increases causing a greater airflow through the blower duct. The increased airflow is sensed by the flow control valve which begins to close.
(1)
AIRPLANES WITH FLOW CONTROL VALVES P/N 10-60704-1 THRU -6; When the differential pressure reaches 2.0 to 2.8 the valve is closed. While the pressure differential is greater than 2.0 to 2.8 psi, the equipment cooling air will exhaust mainly to the forward cargo compartment.
(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. Normal airflow past the low flow sensor probe stabilizes the current required to heat the probe. This current is sensed by the electronic curcuit in the sensor. Loss of airflow causes a change in the current to heat the probe triggering a transistor to supply a ground to the EQUIP COOLING EXHAUST OFF and master CAUTION lights.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITH EFIS ú
21-58-03
ú ú 01 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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.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
_______
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 21-58-03, 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 low airflow sensor, blowers, automatic flow control valve, and blower relays. When trouble shooting the 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.
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