o Shut down the APU and attempt to restart it. If the APU starts
and system pressure is still low, replace the primary hydraulic
pump. If the starter/generator spins, but does not turn the APU
over or the APU fails to start, you must notify support
maintenance to check the pump/starter/generator drive chain.
Backup Hydraulic Pump.
There are two general items that must be checked prior to troubleshooting
the backup hydraulic pump:
o Ensure the suction ball valve from the hydraulic reservoir is
o Check the hydraulic oil level at the reservoir. If it is low,
fill it to the proper level with the approved grade of hydraulic
oil (LO 9-2350-267-12).
The main engine must operate at 1100 RPM for efficient pump
Begin troubleshooting the system at the hand pump selector.
o Ensure the hydraulic system selector valve is in the OUT position
(TM 9-2350-267-10)(Fig. 3F). If the selector valve is not in the
proper position, put it in the OUT position and re-start the
If the selector valve is in the correct position,
continue to troubleshoot the system.
Hand pump pressure must not exceed 150 psi.
o Ensure the hand pump assembly gage indicates between 125-150 psi.
If it does not, make sure you close the dump valve and pump the
hand pump assembly while observing the gage.
If the pressure
gage does not indicate the correct pressure, check the hand pump
hoses and tubing to the bulkhead for leaks.
If you find no
leaks, repair or replace the hand pump.
If the pressure gage
does indicate the correct pressure, continue troubleshooting the
system (Fig. 72).