4. Procedure
_________
 (Ref. Fig. 401/TASK 49-51-54-991-001) Subtask 49-51-54-420-050
 A. Installation of the Bypass Valve
 (1)
 Remove the blanking plugs from the disconnected line ends.

 (2)
 Put the
 new packing (2) on the pipe (1),
 new packing (8) on the pipe (7),
 new packing (10) on the pipe (9).

 (3)
 Install the bypass valve (3) with the washers (5) and the screws (4) on the bracket (6).

 (4)
 Install the pipes (1), (7) and (9) on the bypass valve (3).

 (5)
 Torque the B-nuts of the pipes (1), (7) and (9) to 2.5 m.daN (18.43 lbf.ft).

 Subtask 49-51-54-865-052
 B. Remove the safety clip(s) and the tag(s) and close this(these) circuit breaker(s): 1KD, 2KD
 Subtask 49-51-54-710-050
 C. Do the operational test of the APU (Ref. TASK 49-00-00-710-004).
 (1) Examine the Bypass Valve for air leaks
 (Ref. TASK 49-00-00-790-004).

 NOTE : No leaks are permitted.
____  5. Close-up

________ Subtask 49-51-54-410-050
 A. Close Access
 (1)
 Make sure that the work area is clean and clear of tool(s) and other items.

 (2)
 Set the LIGHT control switch 11LJ to the off position.

 (3)
 Close the APU access doors 315AL, 316AR (Ref. TASK 52-41-00-410-001).

 (4)
 Remove the access platform(s).

 (5)
 Remove the warning notice(s). Subtask 49-51-54-860-052

 B.
 Aircraft Maintenance Configuration

 (1) De-energize the ground service network
 (Ref. TASK 24-42-00-862-001).

 ACCESSORY COOLING - DESCRIPTION AND OPERATION
_____________________________________________

R **ON A/C 001-003, 051-099, 401-499,
 1.
 General

_______ The accessory cooling system operates independently of the APU load compressor and the bleed and surge-air system. A cooling fan supplies sufficient cooling air to the oil cooler to keep the lubricating oil in the correct temperature range. It also supplies cooling air to the APU compartment to remove the heat which comes from the APU surface. The cooling fan is of the one-stage axial-flow type and the accessory drive gearbox turns the cooling fan rotor. The compartment cooling air flows through an outlet into the APU compartment.

 2.
 Component Location

__________________
 (Ref. Fig. 001)

 -------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA
 | | | | DOOR | REF. -------------------------------------------------------------------------------4005KM5 FAN - COOLING 316 316AR 49-52-51
 DUCT - OIL COOLER OUTLET 315 315AL 49-52-41 DUCT - COMPARTMENT COOLING 315 315AL 49-52-52
 3. System Description
__________________ (Ref. Fig. 001, 002) The accessory cooling system supplies air circulation for the oil cooler and for the ventilation of the APU compartment. The accessory cooling system has the subsequent components:
 -
a fan inlet duct,

 -
a cooling fan,

 -
a fan outlet duct,

 -
an oil cooler,

 -
an oil cooler inlet duct,

 -
an oil cooler outlet duct.

 A.
 Cooling Fan

 (1) The cooling fan takes the air from the APU inlet plenum chamber. It supplies this air to the oil cooler (Ref. 49-91-00) and to the APU compartment.

 APU Cooling and Ventilation - Component Location.
 Figure 001

 CES

 APU Cooling and Ventilation - Schematic Diagram
 Figure 002

 CES

 (2)
 The cooling fan takes the air from the APU inlet plenum chamber by suction. The air flows through the cooling fan inlet-duct to the cooling fan. The cooling fan is of the one-stage axial-flow type. It gets mechanical energy from the accessory drive gearbox and uses this energy to make the cooling air flow. A V-clamp attaches the cooling fan to the accessory drive gearbox. The gearshaft assembly of the cooling fan assembly engages with the cooling fan idler of the gearbox.

 (3)
 The air flows into the cooling fan outlet-duct. Some of the cooling air flows through the outlet into the APU compartment. The remaining cooling air flows through the oil-cooler inlet duct to the oil cooler.

 B. Oil-Cooler Cooling Air
 (1)
 The cooling air flows from the cooling fan through the oil cooler inlet duct to the oil cooler. The cooling air which flows through the oil cooler keeps the oil in the correct temperature range. The oil cooler is of the heat exchanger type (Ref. 49-91-00). The cooling fan supplies sufficient air to keep the oil at the correct temperature during all operational conditions of the APU. The hot air then flows through the oil cooler outlet duct into the ambient air.
　
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