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B.  Some installations may have modified the tee fitting by adding a 0.017-0.022-inch diameter orifice vent in upper part of tee. This orifice serves as the acceleration limiter orifice and replaces the orifice originally located in the acceleration limiter housing of the fuel control unit (AMM 49-31-101/601).
CAUTION:  APU MUST HAVE ONLY ONE ORIFICE IN COMPRESSOR DISCHARGE PRESSURE LINE TO ACCELERATION LIMITER. MORE THAN ONE VENT WILL RESULT IN ENGINE DAMAGE DUE TO HUNG STARTS.
2.  Equipment and Materials
A.  Compressed Air Source - 100 psig max.
3.  Prepare to Clean Orifice Tee
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 access door.
D.  Support lower shroud, open shroud latches, and remove shroud.
CAUTION:  EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
4.  Clean Orificed Tee (Fig. 701)
A.  Disconnect control air pressure line at fuel control acceleration limiter tee fitting. Plug control air pressure line.
B.  Disconnect control air pressure line at thermostat selector solenoid valve.
C.  Connect compressed air source (100 psig max) to control air pressure line.
NOTE:  Flow of air indicates that the orifice is unobstructed. If tee has orifice vent in upper part, hold finger over orifice while checking internal orifice for airflow. After flow has been noted, verify air flows through upper orifice. If necessary, use No. 77 drill to clear orifice passage.
D.  Remove compressed air source and connect control air line to thermostat selector solenoid valve.
E.  Remove plug from control air line and connect to acceleration limiter tee fitting on fuel control unit.
Aug 01/95 49-52-91 Page 701 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

G01941
Compressor Discharge Pressure Orificed Tee Cleaning  575 
49-52-91  Figure 701  Feb 15/79 
Page 702 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

F.  APUs WITH ALLIEDSIGNAL SB GTCP85-49-7096;
Examine the air lines for leakage:

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

(2)  
During the APU operation, examine the air lines 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.

G.  APUs WITHOUT ALLIEDSIGNAL SB GTCP85-49-7096;
Examine the air lines for leakage:

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

(2)  
Do the APU normal shutdown (AMM 49-11-0/201).

(3)  
Attach a DO-NOT-OPERATE tag to the APU master switch on the P5 forward overhead panel.

(4)  
Visually examine the air lines for any signs of leakage:

(a)  If you found signs of leakage, repair the cause of it.
5.  Restore Airplane to Normal Configuration
A.  Position lower shroud against upper shroud and close shroud latches.
CAUTION:  MAINTAIN A MINIMUM CLEARANCE OF 0.18 INCH BETWEEN ENGINE PLUMBING, FIRE DETECTOR, CLAMPS AND INSIDE SURFACE OF LOWER SHROUD.
EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
B.  Disengage APU compartment access door support rods and stow rods. Close and latch access door.
C.  Close the circuit breaker on APU control unit on E3-3 electronic shelf.
D.  Position BATTERY switch to ON and remove placards.
501 
Aug 01/95  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  49-52-91 Page 703 

APU CONTROLS - DESCRIPTION AND OPERATION
1.  General (Fig. 1)
A.  The APU controls consist of manual and automatic controls for starting, stopping, and maintaining operation within safe limits. Once an APU start cycle has been initiated, further control of the unit is fully automatic. The APU controls consist of an electronic speed switch, tachometer generator, two oil pressure switches, and an oil temperature switch. Additional control is provided by an APU control thermostat which is discussed in the APU fuel and bleed air sections of this chapter. The automatic control center of the system is the APU control unit, located in the electrical and electronic equipment area. The controls provide correct sequencing of the starting cycle and protection against overspeed, loss of lubricating oil pressure, and high oil temperature.
　
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