Chapter 6 Troubleshooting
UD-series Screw Compressors
6-7
Trouble
Direct causes
Factors
Actions
09 Faulty
indication of
capacity
control posi-
tion
Imprecision in
compressor
indicator
Loose screws for
indicator
Manually tighten screws to the 0%
indication position of compressor
capacity control.
Imprecision in
controller capacity
control indicator
Worn groove of
compressor
indicator cam
Most cases are due to prolonged
partial load operation. In this case,
replace indicator cam.
* Indicator cam that is currently
manufactured has reinforced
groove.
Worn guide pin
(dowel pin) of com-
pressor push rod
Guide pin of compressor push rod is
currently reinforced as well.
However, if only indicator cam has
reinforced groove, wear of guide pin
might occur. Replace dowel pin.
Malfunction in
potentiometer
If cased by aging degradation or
prolonged partial load operation,
replace potentiometer.
If cased by excessive vibration of
compressor, take vibration
reduction measures, and then
replace parts.
Maladjustment of
zero point and span
adjustment for E/E
positioner
Readjust it.
Malfunction of E/E
positioner or its
indicator
For aging degradation, replace E/E
positioner.
For unique causes such as surge
current, remove the causes or take
measures.
Loose terminals or
faulty wiring
For loose terminals, tighten them.
For faulty wiring, replace it.
10
Capacity
control
malfunction
Refer to each factor
in “Imprecision in
controller capacity
control indicator”
above.
Same as on the left
Same as on the left
Undetected 100 %
or 0% by indicator
Malfunction of
micro-switch
Replace micro-switch.
Malfunction of
unloader solenoid
valves or related
relays, etc. for
capacity control
Most cases are due
to coil burnout.
For aging degradation, replace
parts.
For water leakage, etc., remove the
cause and replace parts.
Refer to the solenoid valve
instruction manual for details.
Internal leakage of
unloader solenoid
valves for capacity
control
Expanded oil and
refrigerant liquid
trapped inside
unloader cylinder
due to temperature
increases.
If caused by prolonged low load
operation, improve by re-examining
the operation method.
Install a capacity control hydraulic
line with an in-line check valve
(internal reversal-stoppage valve)
and an oil bypass line.
