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Service Manual
Troubleshooting
Overview
Neutral difficult or impossible to find
Item
Input to pump control
Pump displacement control
Multifunction valve
System operating hot
Item
Oil level in reservoir
Heat exchanger
Charge pressure
Charge pump inlet vacuum
System relief pressure settings
For internal leakage in motor
System pressure
Transmission operates normally in one direction only
Item
Input to pump control
Pump displacement control
System pressure limiters, high
pressure relief valves, or system
check valves
Charge pressure
Series 90 Pumps
This section provides general steps to follow if certain undesirable system conditions occur. Follow the
steps in a section until you solve the problem. Some of the items are system specific. For areas covered in
this manual, we reference the section. Always observe the
section
and those relating to your specific equipment.
Description
Input to control module is operating improperly.
Control linages are not secure, control orifices are
blocked.
Multifunction valve is leaking.
Description
Insufficient hydraulic fluid will not meet cooling
demands of system.
Heat exchanger is not sufficiently cooling the system. Check air flow and input air temperature for heat
Low charge pressure will overwork system.
High inlet vacuum will overwork system. A dirty filter
will increase the inlet vacuum. Inadequate line size
will restrict flow.
If the system relief settings are too low, the relief
valves will be overworked.
Leakage will reduce low side system pressure and
overwork the system.
High system pressure will overheat system.
Description
Input to control module is operating improperly.
Control linkages are not secure, control orifices are
blocked.
Interchanging the multi-function valves will show if the
problem is related to the valve functions contained in
the multi-function valves.
If charge pressure decays in one direction, the loop
flushing valve may be sticking in one direction.
520L0818 • Rev 0101 • August 2015
safety precautions
listed in the
Action
Check control input and repair or replace as necessary.
Adjust, repair, or replace control module as necessary.
Swap multifunction valves. If system changes direction,
replace defective valve.
Action
Fill reservoir to proper level.
exchanger. Clean, repair, or replace heat exchanger.
Measure charge pressure. Inspect and adjust or replace
charge relief valve, or repair leaky charge pump.
Check charge inlet vacuum. If high, inspect inlet filter and
replace as necessary. Check for adequate line size, length
or other restrictions.
Verify settings of pressure limiters and high pressure relief
valves and adjust or replace multi-function valves as
necessary.
Monitor motor case flow without loop flushing in the
circuit (use defeat spool). If flow is excessive, replace motor.
Measure system pressure. If pressure is high, reduce loads.
Action
Check control input and repair or replace as necessary.
Repair or replace control module as necessary.
Interchange multi-function valves. If the problem changes
direction, repair or replace the valve on the side that does
not operate.
Measure charge pressure in forward and reverse. If pressure
decays in one direction, inspect and repair the motor loop
flushing valve.
Introduction
25
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