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B.  The high oil temperature light and the low oil pressure light are connected to the APU annunciator light and to the master caution lights, located on the center instrument panel (Fig. 1). When any one or a combination of the APU indicating lights are energized, the APU annunciator light and the master caution lights are energized (Ref Master Caution and Warning Lights, 33-15-0). The low oil quantity light is not incorporated in the annunciator light and master caution light circuit.
C.  Each APU indicating light can be tested individually by pressing the light, or all lights can be tested simultaneously when the master test switch is actuated.
2.  High Oil Temperature Light
A.  The high oil temperature light is energized when the APU oil temperature reaches approximately 250°F (121°C) or 285°F (140°C). At this temperature, the oil temperature switch closes and completes the light circuit. For the high oil temperature switch description, refer to APU Controls, 49-61-0.
3.  Low Oil Pressure Light
A.  The low oil pressure light is energized when the APU oil pressure is too low to operate the APU. The light is on while the APU engine builds up oil pressure during the engine start. When the oil pressure reaches approximately 55 psig, the low oil pressure switch actuates and the low oil pressure light is extinguished. During the APU operation, if the oil pressure drops to approximately 45 psig, the low oil pressure switch again actuates and the low pressure light is energized. For description of the low oil pressure switch, refer to APU Controls, 49-61-0.
500 
Nov 15/80  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  49-94-0 Page 1 

4.  Low Oil Quantity Light
A.  The low oil quantity light is energized when the APU oil quantity drops to 1-1/2 quarts and below. (Oil tank capacity is 1-3/4 U.S. gallons.) At this time the oil quantity microswitch closes and completes the light circuit.
5.  Oil Level Switch
A.  The oil level switch consists of a tube, float, and magnetically controlled microswitch. The microswitch is float actuated when the oil tank oil quantity drops to 1-1/2 quarts or below. The oil level switch is located on the bottom end of the APU oil tank (Fig. 1).

G20537G20562
APU Oil Indicating System Component Location  511 
49-94-0  Figure 1 (Sheet 1)  Nov 01/74 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

526  APU Oil Indicating System Component Location 
Aug 15/72  Figure 1 (Sheet 2)  49-94-0 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

OIL LEVEL SWITCH - REMOVAL/INSTALLATION
1. Prepare to Remove Oil Level Switch
A.  Position BATTERY switch and APU master switch to OFF and placard that APU maintenance is "in work."
B.  Open the circuit breaker on M280 module-APU control unit on E3-3 electronic shelf.
C.  Open APU compartment access door latches and open door. Install door support rods.
D.  Support lower shroud, open shroud latches, and remove shroud.
CAUTION:  EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
E.  Drain oil tank (AMM 49-91-31/301).
2.  Remove Oil Level Switch (Fig. 401)
A.  Disconnect electrical plug from receptacle, remove receptacle from bracket, and detach clamps holding wire sleeve to electrical conduit.
B.  Remove screws and washers attaching oil level switch to oil tank.
C.  Remove oil level switch, 0-ring and backup ring from oil tank. Discard O-ring.
NOTE: Retain backup ring for installation with replacement switch.
3.  Install Oil Level Switch (Fig. 401)
A.  Install new O-ring and backup ring on oil level switch.
B.  Insert oil level switch in oil tank and secure with four screws and washers.
C.  Attach electrical receptacle to bracket and secure with four screws, washers, and nuts. Connect electrical plug to receptacle.
D.  Clamp wiring sleeve to electrical conduit.
E.  Fill oil tank (AMM 49-91-31/301).
F.  Position BATTERY switch to ON and remove placard.
G.  APUs WITH ALLIEDSIGNAL SB GTCP85-49-7096;
Examine the oil level switch for leakage:

(1)  
Start and operate the APU (AMM 49-11-0/201).

(2)  
During the APU operation, examine the oil level switch for leakage.

(3)  
Do the APU normal shutdown (AMM 49-11-0/201).

(4)  
Attach a DO-NOT-OPERATE tag to the APU master switch on the P5 forward overhead panel.

(5)  
If you found leakage, repair the cause of it.
　
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