Chapter 6 Troubleshooting
UD-series Screw Compressors
6-2
Trouble
Direct causes
Factors
Actions
02 Compressor
stops imme-
diately after
startup.
Low pressure
protection circuit
activated
Insufficient refriger-
ant circulation
volume
If any heat exchange failures as
typified by poor defrost
performance, investigate the cause
and take measures.
For malfunction in pressure
regulating valve operation, replace
pressure regulating valve, or
remove the cause.
Malfunction of low
pressure protection
device, pressure
sensor, relays, etc.
Identify malfunctioning devices,
examine their causes, and take
measures.
Then, replace malfunctioning
devices.
Motor overload
In many cases, motor overload that occurs just after startup is
caused by the motor, not by the refrigeration cycle.
Refer to
the motor instruction manual.
03 Abnormally
low
pressure
(low suction
pressure)
Refer to the direct
causes “Low
pressure protection
circuit activated” in
item 2.
Same as on the left
Same as on the left
04
Low
oil-supply
pressure
Clogging in oil filter
element
* Big difference in
outlet/inlet
pressures
Contamination of
lubricant
Remove clogging. Check oil
contamination level and change
lubricant as necessary.
Defect inside
compressor
Check oil contamination level. After
vibration noise diagnosis, overhaul
compressor as necessary.
Insufficient oil
amount in oil
separator
Malfunctioning oil
heater, excessive
refrigerant dissolu-
tion during
stoppage, thus
resulting in oil carry
over during startup.
Inspect oil heater.
Inspect relays, etc., on related
circuits.
And replace parts as needed.
Insufficient oil
return caused by
insufficient
refrigerant
circulation
Resolve insufficient volume of
refrigerant circulation, and then
return oil from load side heat
exchanger.
* Charge lubricant temporarily.
Troubles such as
clogging in oil
return circuit
Remove any causes of trouble to
restore.
Extensive oil leak
Inspect machine room and around
compressor and take measures.
Inspect for presence of oil floating in
cooling water system.
If there is any oil floating, check for
oil leak in oil cooler heat exchanger
tube, and take measures.
For damage in pipes, etc., caused
by excessive vibration, take
vibration reduction measures
(including sympathetic vibration
measures).
