Manitowoc Published 10-01-2012, Control # 045-08 10-21
777 SERVICE MANUAL TROUBLESHOOTING
10
Problem 19
Closed-loop hydraulic system response is sluggish.
POSSIBLE CAUSES
Low hydraulic oil level in reservoir; Low hydraulic oil temperature; Reservoir shut-off is partially closed;
Dirty charge filter; System multifunction valves are not set correctly; Pump or motor problem.
CHECKS
Hydraulic oil level in reservoir, reservoir shut-off valve is fully open,
and hydraulic oil above 60°F.
Yes
No
Yes No
Yes No
No
Yes
With pump in neutral, is system charge pressure
at more than 350 psi at diagnostic display screen?
Fill reservoir to correct level, warm hydraulic
oil to 60°F, or open shut-off valve.
Does tank filter read less than 7 psia on diagnostic display screen?
Check and replace suction filter if required.
Adjust charge pressure relief valve for 350 psi. (See Test 15.)
350 psi Obtained 350 psi not Obtained
System multifunction valves operating at recommended
system pressure?
Adjust or replace problem valve.
Check for internal leakage at pump and motor. (See Test 18.)
Normal High Leakage
Check control pressure at pump ports M4 and M5 and
motor ports M7 and M8. (See Tests 9 and 10.)
Pressure Ok Pressure Not Ok
Consult dealer/factory.
Repair or replace pump EDC
or motor PCP, as required.
Repair or replace pump
or motor as required.
System operating
properly.
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