(f)  
Push the LSK that is adjacent to <PNEUMATICS to show the GROUND TESTS menu for the pneumatic system.

 (g)  
Push the LSK that is adjacent to the <BLEED SYS ELEC prompt.

 1)  When the TEST PRECONDITIONS page shows, make sure each instruction on the page is completed. (Push the NEXT PAGE key to show the subsequent pages.)
 2)  Push the LSK that is adjacent to the START TEST>.
 NOTE: IN PROGRESS shows during the tests.
____
 (h)  When IN PROGRESS goes out of view, look for PASS or FAIL> adjacent to the <BLEED SYS ELEC prompt.
 NOTE: If a PASS indication shows, no failures occurred
____
 during the test.

 1) If FAIL> shows: a) Push the LSK that is adjacent to FAIL> to see the GROUND TEST MSG pages for the failure. b) Push the NEXT PAGE key until you find all the GROUND TEST MSG pages. c) Make a list of all CMCS messages, CMCS message numbers, and ATA numbers that show on the GROUND TEST MSG pages.
 d)  Go to the CMCS Message Index of the Fault Isolation Manual (FIM) to find the corrective action for each CMCS message.
 E.  Put the Airplane to Its Usual Condition
 S 864-009
 (1) Remove electrical power if it is not necessary (Ref 24-22-00/201).
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747-400 MAINTENANCE MANUAL
 BLEED AIR PRECOOLER SYSTEM - DESCRIPTION AND OPERATION
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General
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 A.  The precooler reduces the temperature of the bleed air extracted from the engines. Each engine has a precooler, fan air temperature sensor, and a fan air modulating valve.
 B.  The precooler is installed on the bottom of the strut above the engine compressor case. The precooler uses the air that flows from the fan section to decrease the temperature of the bleed air.
 C.  The fan air temperature sensor will supply a control signal for the fan air modulating valve. If the temperature of the bleed air becomes too high, the sensor will use fan air pressure to tell the valve to open. This will permit cool fan air to go to the precooler.
Bleed Air Precooler (Fig. 1)
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 A.  The precooler is an air-to-air heat exchanger. It uses a crossflow configuration to remove heat from the bleed air. Bleed air goes into the precooler at the bottom forward section. Fan air goes into the precooler on the right side and goes out of the precooler exhaust flange on the left side.
Fan Air Temperature Sensor (Fig. 1)
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 A.  The fan air temperature sensor is installed on the pneumatic duct in the left side of the strut. The sensor is in a position that is upstream from the pressure regulating and shutoff valve (PRSOV).
 B.  The fan air temperature sensor has a signal pressure port, cooling air port, and a temperature probe that goes into the pneumatic duct. It also has an insulation blanket. The temperature probe measures the temperature of the air in the pneumatic duct.
Fan Air Modulating Valve (Fig. 1)
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 A.  The fan air modulating valve is installed on the right side of the precooler.
 B.  The valve is a 9-inch butterfly type. It is spring loaded to the open position. The valve has three pressure tubes connected to it, a locking crank, an actuator, and two position switches.
 C.  The actuator is pneumatically operated by precooler pressure when it receives a signal from the fan air temperature sensor. The locking crank permits you to manually move the valve. The two position switches are used to tell the Air Supply Control and Test Unit (ASCTU) when the valve is in the open or closed position.
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747-400
MAINTENANCE MANUAL