Troubleshooting overview
This section serves as a guide for identifying and resolving undesirable system conditions.
Please observe the safety concerns listed in
and the precautions related to relevant
equipment when resolving system issues.
DDC20/24 system operating hot
Cause
Problem
Solution
Oil level in reservoir. Insufficient hydraulic fluid will not meet cooling demands of
system.
Fill reservoir to proper level.
Heat exchanger.
Heat exchanger 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/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 high pressure relief valves and 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.
DDC20/24 transmission operating normally in one direction only
Cause
Problem
Solution
Control linkage
Control linkage operating improperly
Repair/replace control linkage
High pressure relief
valve
Malfunctioning HPRV can affect one direction while the other
functions normally.
Exchange the high pressure relief valves. If the problem
changes direction, replace the valve that does not operate
correctly. Settings may be different for forward/reverse.
DDC20/24 system noise or vibration
Cause
Problem
Solution
Oil level in reservoir Low oil level leads to cavitation.
Fill reservoir.
Aeration of the oil/
pump inlet vacuum
Air in system decreases efficiency of units and controls. Air in
system is indicated by excessive noise in pump, foaming in oil,
and hot oil.
Find location where air is entering into the system and fix.
Check that inlet line is not restricted and is proper size.
Cold oil
If oil is cold, it may be too viscous for proper function and cause
cavitation
Allow the oil to warm up to its normal operating temperature
with engine at idle speed.
Pump inlet vacuum High inlet vacuum causes noise/cavitation.
Check that inlet line is not restricted and is proper size. Check
filter and bypass valves (if present).
Shaft couplings
A loose shaft coupling will cause excessive noise.
Replace loose shaft coupling.
Shaft alignment
Misaligned shafts creates noise
Align shafts.
Charge/High
pressure relief
valves
Unusual noise may indicate sticking valves. Possible
contamination.
Clean/replace valves and test pump. May be a normal
condition.
DDC20/24 system will not operate in either direction
Cause
Problem
Solution
Oil level in reservoir Low oil level leads to cavitation.
Fill reservoir.
Open bypass valve
If bypass valve is open, the system loop will be depressurized.
Close bypass valve.
Service Manual
DDC20/24 Axial Piston Pumps
Troubleshooting
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©
Danfoss | August 2019
L1120413 | AX00000135en-000401