Danfoss 90 Series Service Manual

System will not operate in either direction
Item Description Action
Oil level in reservoir Insufficient hydraulic fluid to supply system loop Fill reservoir to proper level.
Input to pump control Input to control module is operating improperly Check control input and repair replace as necessary.
Pump displacement control Control linkage is not secure, control orifices are
blocked, etc.
Repair or replace control module as necessary.
Bypass valve(s) open If bypass valve(s) are open, the system loop will be
depressurized.
Close bypass valves. Replace multi-function valve if
defective.
Charge pressure with pump in
neutral
Low charge pressure is insufficient to recharge system
loop.
Measure charge pressure with the pump in neutral. If
pressure is low, go to Pump charge relief valve; otherwise
continue with Charge pressure with pump in stroke.
Charge pressure with pump in
stroke
Low charge pressure with the pump in stroke indicates
a motor charge relief valve or system pressure relief
valve may be improperly set.
Measure charge pressure with pump in stroke. If pressure is
low, adjust or replace motor charge relief valve, otherwise
go to Charge pumps.
Pump charge relief valve A pump charge relief valve that is leaky or set too low
will depressurize the system.
Adjust or replace pump charge relief valve as necessary.
Charge pump inlet filter A clogged filter will under supply system loop. Inspect filter and replace if necessary.
Charge pumps A malfunctioning charge pump will provide insufficient
charge flow.
Repair or replace the charge pump.
Pump displacement control Control linkages are not secure, control orifices are
blocked.
Repair or replace control module as necessary.
System pressure Low system pressure will not provide power necessary
to move load.
Measure system pressure. Continue to next step.
System multi-function valves Defective multi-function valves will cause system to
pressure to be low.
Repair or replace multi-function valve(s).
Low motor output torque
Item Description Action
System pressure at motor Low system pressure at the motor will reduce torque Measure system pressure at motor. If pressure limiter
setting is low, increase setting.
Variable motor stuck at minimum
displacement
Minimum motor displacement yields low output
torque.
Check control supply pressure or repair displacement
control. Check motor control orifices.
Internal leakage Internal leakage will reduce system pressure. Check for leaking O-rings, gaskets and other fittings. Repair
unit as required, or replace leaking unit.
Improper motor output speed
Item Description Action
Oil level in reservoir Insufficient hydraulic fluid will reduce motor speed. Fill oil to proper level.
Pump output flow Incorrect outflow will affect output speed. Incorrect
output flow indicates the swashplate is out of position.
Measure pump output and check for proper pump speed.
Ensure the pump is in full stroke.
Variable motor displacement
control
If variable motor displacement control is not
functioning correctly, variable motor swashplate may
be in wrong position.
See if variable motor displacement control is responding. If
not, repair or replace control.
Internal leakage Internal leakage will reduce system pressure. Check for leaking O-rings, gaskets, and other fittings. Repair
unit as required, or replace leaky unit.
Service Manual Series 90 Pumps
Troubleshooting
26 520L0818 • Rev 0101 • August 2015

Danfoss 90 Series Specifications

General

Brand	Danfoss
Model	90 Series
Category	Water Pump
Language	English