S 415-054

 (4)
Install the Control Display Units (CDUs) of the Flight Management Computer System (FMCS), on the P9 panel (AMM 34-62-11/401).

 S 865-056

 (5)  
Remove the electrical power if it is not necessary
 (AMM 24-22-00/201).

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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A
737-300/400/500MAINTENANCE MANUAL
 EFIS COOLING SYSTEM - DESCRIPTION AND OPERATION
_______________________________________________
General
_______
 A.  The EFIS Cooling System cools the Captain's and First Officer's EHSI and EADI in the control cabin and the IRUs (Inertial Reference Units) in the E/E compartment.
 B.  Cabin air from the E/E compartment is the cooling medium. Air is drawn through a filter by one of two fans through a check valve and delivered to the using units over a low flow sensor. A portion of the fan air is discharged into the open area beside the wheel well through a fixed orifice.
 C.  Air passes through the EHSI, EADI and is discharged below the floor to prevent smoke incursion into the control cabin in the event of an electrical problem with the fans or with units in the E/E compartment.
Filter Assembly
_______________
 A.  The filter assembly is a box containing a cleanable, centrifugal element. Air flowing through the filter is swirled with the denser particles being thrown to the outside and purged through a line connected to the equipment cooling exhaust port.
Normal and Alternate Cooling Fans
_________________________________
 A.  The normal and alternate cooling fans are single stage vaneaxial fans intergrating the motor into the fan. The fan contains an inner housing which encases the three-phase motor. The rotating impeller pushes air over the motor housing and through de-swirl vanes before exiting the fan. Three miniature thermostats serve as thermal protective devices for the fan. The thermostats are connected in series with one located over a coil in each phase.
Normal and Alternate Check Valves
_________________________________
 A.  A two section swing check valve, spring loaded closed, is located down stream of each fan to prevent back flow of air through the fan that is not operating.
Low Flow Sensor
_______________
 A.  The low flow sensor provides warning when the EFIS cooling system is not supplying enough cooling air for safe electronic equipment operation. The airflow detection system consists of an equipment cooling supply OFF warning light and an airflow sensor. Electrical power for operation of the airflow sensor and OFF light press-to-test circuit is taken from the 28-volt dc bus on circuit breaker panel P18. The OFF light is also connected to the master test circuit.
 B.  The low flow sensor is a heated probe with associated electronic circuitry to measure the current required to heat the probe when the proper amount of cooling air flows past. Loss of air flow will change the current required to heat the probe, triggering the transitorized monitoring circuit which supplies a ground to the EFIS indication control relay.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITH EFIS ú

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 ú ú 02 Page 1 ú Jul 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
LOW FLOW SENSOR

EFIS Cooling Component Location
Figure 1

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITH EFIS ú

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 ú ú 02 Page 2 ú Jul 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

EFIS Cooling System
Figure 2

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APLS WITH EFIS ú
　
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