APU Testing - TM-55-4920-424-13-P0142

TM 55-4920-424-13&P

g. Move the MASTER switch on APU Tester box to the UP position.

h. Move the LOCAL/REMOTE switch on the APU Tester box to the UP (Remote) position.

i. Move the FUEL BOOST PUMP switch on the instrument panel to ON. Let run approximately 30 seconds, then

OFF. Check fuel system for leaks.

WARNING

Post fire watch.

j. Move the RUN-START-STOP switch on APU Tester box to the UP (RUN-START) position.

(1) Battery volts drop, %RPM increases, at approximately 5% RPM both START FUEL lights ON and EGT

starts to increase.

(2) At (+,-) 14% RPM, both MAIN FUEL lights ON.

(3) At (+,-) 70% RPM, START FUEL light OFF.

(4) At approximately 90% + 1.5 seconds, MAX FUEL light ON.

(5) At (+,-) 102% RPM, both READY TO LOAD lights ON.

CAUTION

If any abnormal condition is observed/heard during APU operation, place the OFF-

RUN-START switch on instrument panel to OFF IMMEDIATELY. Do not turn off

master switch until engine speed RPM is zero.

CAUTION

If APU is to be restarted or another start attempt tried, wait at least 30 seconds

after APU has stopped before placing START/RUN-STOP switch to START/RUN.

This allows residual fuel to drain from APU, thereby preventing an overspeed or

overtemp condition.

CAUTION

If APU Test stand is allowed to run out of fuel the APU fuel control may be

damaged.

k. Refer to TM 55-4920-431-13, figure and table 2-1 for specific controls and indications of the APU Tester box.

Also refer to the appropriate TM for adjustment and trouble shooting procedures for your APU.

3-14. APU Testing. After APU has automatically accelerated to rated speed, it is protected by three automatic safety

devices; a speed switch, a high exhaust temperature device, and a low oil pressure switch. Refer to appropriate TM for all

adjustment procedures.

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