(2)  
The Fault Isolation procedure below tells you how to find the cause of smoke in the APU pneumatic air supply, the No. 1 engine, the pneumatic air supply from the No. 1 engine, the left pack, the recirculation system,and the related air distribution ducts.

 B. Possible Causes:
 (1)  
Contamination in the Engine No. 1 pneumatic system.

 (2)  
Contamination in the APU pneumatic system.

 (3)  
Hydraulic Fluid Leakage.

 (4)  
Contamination in the air distribution system.

 (5)  
Overheating of the recirculation fan.

 C. Fault Isolation Procedure:
 (1)  Do these checks of the air recirculation system:
 (a)  
Remove the Recirculation Fan Filter (AMM 21-21-23/401).

 (b)  
Examine the air recirculation filter to see if it is necessary to replace it. If it is necessary to install a new air recirculation filter, do the Recirculation Fan Filter Installation (AMM 21-21-23/401).

 (c)  
Do a Operational Test of the Recirculation Fan System (AMM 21-21-22/501) to see if the air recirculation fan or the related wiring generates smoke while it operates.

 (d)  
If there is smoke from the air recirculation fan or the related wiring, then do the applicable steps below: 1) Replace the air recirculation fan. These are the tasks:

 Recirculation Fan Removal (AMM 21-21-22/401) Recirculation Fan Installation (AMM 21-21-22/401) 2) Repair the applicable wiring.
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 3) Do the Repair Confirmation at the end of this task.
 (e)  If no smoke or fumes come from the air recirculation fan or the related wiring, and the operational test is satisfactory, then continue.
 (2)  Do these checks for contamination in the APU pneumatic system:
 NOTE: If you know that smoke or fumes appear in the flight
____ compartment or the passenger cabin when the APU is running but the engines are shut down, go directly to the APU and bleed air inspection tasks that follow.
 (a)  
Start the APU (AMM 49-11-00/201).

 (b)  
When the APU has stabilized, supply conditioned air to the airplane from the APU, through the left pack (AMM 21-00-00/201).

 (c)  
If smoke or fumes come from the APU bleed air supply do these steps: 1) Inspect the APU (AMM 49-11-00/601) for leakage and oil

 contamination. a) If you find indications of leakage, repair the leakage. 2) Do an APU pneumatic duct inspection check (AMM 36-19-15/601).
 3)  If you find indications of leakage, do these steps: a) Do the corrective action indicated in the procedure. b) Do the repair confirmation at the end of the task.
 (d)  If no smoke or fumes come from the APU bleed air supply, and the operational test is satisfactory, do an APU Usual Shutdown (AMM 49-11-00/201), and continue.
 (3)  Do these checks for contamination in the Engine No. 1 pneumatic system:
 (a)  
Do an External Oil System Inspection (AMM 79-00-00/601), and look for leakage of oil in Engine No. 1.

 (b)  
Do an Engine Vents and Drains Inspection (AMM 71-71-00/601) and look for indications of leakage of oil, hydraulic fluid, or fuel in Engine No. 1.

 NOTE: It is not necessary to do this task again if you did
____ it during the external oil system inspection.
 (c)  
If you find indications of leakage in Engine No. 1, then do these steps: 1) Do the corrective action shown in the inspection procedures

 or repair the leakage problems that you find. 2) Do the Repair Confirmation at the end of this task.

 (d)  
If you do not find indications of external leakage, do the Check Engine No. (1, 2) - Smoke/Fumes in the Cabin procedure (AMM 71-00-00/601), and look for indications of oil leakage internal to the engine.

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