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Neutral Difficult or Impossible to Find
Item
Description
Action
Input to pump control
Input to control module is operating improperly
Disconnect input and check to see if pump comes back to
neutral.
•
If Yes – input fault, replace or repair external controller
•
If No – go to next step
Neutral
Neutral set improperl
Shunt servo gauge ports (M4 and M5) together with
external hose and see if pump comes back to neutral.
•
If Yes – Control neutral improperly set (see
•
If neutral is still impossible to set, balance the swashplate
(see
•
If you still cannot set neutral, replace the control.
Transmission Operates Normally in One Direction Only
Item
Description
Action
Input to pump control.
Input to control module is operating improperly.
Check control input and repair or replace as necessary.
Control orifices
Control orifice(s) are blocked.
Clean control orifices.
Control screens
Control screen(s) are blocked.
Replace control screens. Only a Danfoss Authorized Service
Center may remove the unit’s endcap without voiding the
warranty.
Exchange system pressure
limiters
Exchanging the pressure limiter valves will show if the
problem is related to the valve function.
If the problem changes direction, replace the valve that
does not operate correctly.
Exchange high pressure
relief valves
Exchanging the high pressure relief valves will show if the
problem is related to the valve function.
If the problem changes direction, replace the valve that
does not operate correctly.
Servo pressure low or
decaying
Damaged servo seals may prevent servo piston from
stroking the pump.
Check for torn/missing servo seals. Replace and retest. Only
a Danfoss Authorized Service Center may remove the servo
piston without voiding the warranty.
Bypass function open
Open bypass will cause one or both directions to be
inoperative.
Close bypass function.
System Operating Hot
Item
Description
Action
Oil level in reservoir
Insufficient hydraulic fluid will not meet cooling demands
of system.
Fill reservoir to proper level.
Heat exchanger
Heat exchanger is not sufficiently cooling the system.
•
Check air flow and input air temperature for heat
exchanger
•
Clean, repair or replace heat exchanger
Charge pressure
Low charge pressure will overwork system.
•
Measure charge pressure.
•
Inspect and adjust or replace charge relief valve.
•
Inspect charge pump; repair or replace charge pump.
Charge pump inlet vacuum
High inlet vacuum will overwork system.
A dirty filter will increase the inlet vacuum. Inadequate line
size will restrict flow.
•
Check charge inlet vacuum. If high, inspect inlet filter
and replace as necessary
•
Check for adequate line size, length or other restrictions
System relief pressure
settings
If the system relief valves are worn, contaminated, or valve
settings are too low, the relief valves will be overworked.
Verify settings of pressure limiters and high pressure relief
valves and adjust or replace valves as necessary.
System pressure
Frequent or long term operation over system relief setting
will create heat in system.
Measure system pressure. If pressure is too high, reduce
loads.
Service Manual
H1P 069—H1P 280 Axial Piston Single Pumps
Troubleshooting
©
Danfoss | January 2021
AX152886482551en-000601 | 31