Table 21: Compressor unit, general issues
Symptom
Probable cause
Solution
Oil filter differential pressure
too high
Oil filter clogged
Replace oil filter
Valves in oil system are not fully
open
Check stop valves and the
opening position of the oil
regulation valve
3-way oil temperature
control valve. Water-cooled
or refrigerant-cooled
(Thermosyphon)
Check function, and replace the
sensor element
Insufficient oil cooling function,
water-cooled
Check oil cooler, fouling, water
inlet temperature,(too high),
and water flow (too low)
Insufficient oil cooling function,
refrigerant-cooled
Check and if necessary drain
accumulated oil in the oil
cooler. Check that the gravity
fed refrigerant system is fully
flooded
Insufficient oil cooling function,
liquid injection
Check the settings in control
system, valves, and the strainer
in the liquid injection line
Oil temperature too high, and
high discharge temperature
Compressor protection valve is
open or leaking
Check the discharge pressure
safety cut-out settings. Check
the pilot and main protection
valve
Excessive liquid in suction line
or liquid slugging
Check the evaporator (and
economiser, optional), and
the expansion valve function.
Decrease the rate of the
evaporator temperature pull
down
Discharge temperature very
low. Oil temperature low
and oil may be foaming in oil
separator
Liquid injection (optional)
overfeeding
Check the settings in the
control system (increase the set
point). Check the stability of the
liquid injection
Compressor protection valve is
opening or leaking
Check the discharge pressure
safety cut-out settings. Check
the pilot and main protection
valve
Oil return valve fully open
Adjust the regulating valve
according to manual
Suction pressure high and
insufficient refrigeration
capacity
Suction strainer clogged
Clean the strainer
SAB 283-355 A-Frame OHU 6042 and OHU 7650 (including ATEX) Screw Compressor Unit
64
