JLG sky trak mmv Service Manual page 352

Hydraulic System
Before troubleshooting any
hydraulic circuit, ALWAYS
begin by checking the
following:
1. Hydraulic oil level in the
reservoir
2. All hoses, tubes, fittings
for leaks, kinks,
interference, etc.
3. Air in the lines
NOTE:
When checking pressures in
circuits, refer to Section 9.7,
Hydraulic System Testing for
correct pressure readings.
9.54
If the pump is not
functioning properly,
check the suction line from
the reservoir.
If OK
Check the oil flow
to the pump.
If the cooler is not cooling
the oil, check that the
radiator and cooler are not
clogged or obstructed.
If OK
Inspect the check valve in the
cooler hydraulic line.
If OK
Refer to Section 10.13.4,
Hydraulic Oil Temperature
Switch .
If the unloader valve is not
functioning properly,
check the pressure and
flow to the valve.
If OK
Check the main system
pressure at the "VG" port of
unloader valve.
If OK
Check the differential
pressure sense valve on the
unloader valve.
If OK
Check pump flow.
If OK
Check the suction line from
the reservoir.
Not
Repair/replace suction line.
OK
Not
Repair/replace pump.
OK
Not
Clean radiator and cooler.
OK
Not
Replace check valve.
OK
Adjust/repair/replace the
Not
relief valve on the
OK
unloader valve.
Repair/replace the differential
Not
pressure sense valve on the
OK
unloader valve.
Not
Repair/replace pump.
OK
Not
Repair/replace suction line.
OK
Model MMV Rev. 12/04