TM 9-6115-664-13&P
Section V. UNIT TROUBLESHOOTING
4-9. GENERAL.
This section contains unit level troubleshooting information and tests for the APU. Troubleshooting logic trees will
help in locating and correcting minor APU malfunctions. Each malfunction or trouble symptom is addressed and is
followed by a series of inspections or tests necessary to determine the probable cause and corrective action.
4-10. TROUBLESHOOTING.
a.
This chapter does not list all possible malfunctions that may occur, all tests or inspections that may be performed,
or all corrective actions for each malfunction. Only those checks and tests authorized for the unit level are covered. If a
malfunction is not listed, or is not remedied by corrective actions, notify personnel at a higher maintenance level.
b.
Prior to using troubleshooting diagrams, be sure you have performed all normal operational checks. Refer to the
system electrical schematic (Figure FO-1) , wiring diagrams, and LED and Test Point Table (Table 4-4) for assistance in
troubleshooting electrical components.
c.
Refer to Table 4-3, Malfunction Index, for determining applicable troubleshooting procedure.
Table 4-3. Malfunction Index
Table
ENGINE
Engine will not crank
4-5
Engine will not crank, control panel circuit breaker trips continuously
4-6
Engine cranks but will not start
4-7
Engine will not start in cold weather
4-10
Engine starts and stops
4-11
Engine speed fluctuates
4-12
Engine overheats
4-13
Engine hammers
4-14
Engine emits black smoke
4-15
Engine emits white smoke
4-16
FUEL SYSTEM
Fuel system will not energize, no fuel to the APU
4-9
GENERAL SYSTEM MALFUNCTIONS
Engine operates, but no generator voltage or below rated voltage
4-8
APU shutdown, low oil pressure
4-17
Engine start / hold solenoid does not stay engaged
4-18
4-11
