Starting

TM 55-4920-424-13&P

Note

If APU does not light off because of entrapped air in APU fuel system, loosen

electrical connector from fuel pressure switch, but keep connector engaged.

Crank APU and disconnect pressure switch connector at 10 percent speed. As

soon as APU lights off, reconnect connector, and tighten securely.

h. Observe that APU accelerates smoothly to 102 percent speed.

WARNING

Exhaust duct and APU combustor section are hot during operation. Keep clear of

combustibles. Avoid physical contact to preclude personal injury.

i. To charge battery, allow APU to reach operating speed. Move DC GEN ON-OFF/RESET switch to ON. DO NOT

OVERCHARGE BATTERY . Press button on dc volt-ammeter to read dc volts. Refer to TM-11-6140-203-15-1 for

charging times.

j. If EXHAUST TEMP indicator indicates abnormally high (or low) temperatures during starting, adjust APU fuel

control unit. Refer to paragraph 3-10 for fuel control adjustment procedure.

k. If 90% SEQ CHECK light does not extinguish, or extinguishes before 90 percent engine speed is reached, adjust

speed switch. Refer to TM 55-2835-203-24 for adjustment procedure.

l. If LOW OIL PRESS light does not extinguish after APU cranking is initiated, APU lubricating oil system or low oil

pressure switch has malfunctioned. Stop cranking APU and correct malfunction before initiating another start.

Refer to TM 55-2835-203-24 to correct this malfunction.

m. If cranking cycle is accomplished without a lightoff, fuel control unit (fuel pump or acceleration control), ignition

exciter, spark plug, or fuel nozzles may be malfunctioning. Refer to TM 55-2835-203-24 for corrective

procedures.

CAUTION

Do not attempt to restart APU after a malfunction shutdown until malfunction has

been corrected.

n. If APU shuts down because of overspeed, the OVERSPEED light will illuminate. The APU fuel control unit, speed

switch, or main fuel solenoid valve may be malfunctioning. Refer to TM 55-2835-203-24 for corrective

procedures.

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