Johnson Controls SABROE UniSAB III Engineering Manual page 121

Compressor control and surveillance
During operation, the oil pump is started and stopped in accordance with the compressor differential
pressure (discharge pressure - suction pressure). The difference is set in the picture Oil/ Pressure/Con-
trol where Set point 1 and Set point 2 will appear.
Set point 1 is the pump start pressure and Set point 2 is the pump stop pressure. Therefore, Set point 1
must be set for the lowest pressure level.
If the compressor differential pressure is below Set point 1 during operation, the pump will start immedi-
ately. When the compressor differential pressure has been higher than Set point 2 for 60 seconds, the
pump will stop.
Starting sequence
When the compressor has received starting permission, UniSAB III will check if the capacity slide is in
minimum position. If the capacity slide is higher than a 5% position, the solenoid valve for decreasing ca-
pacity slide position is activated, and, if equipped with oil pump, the oil pump is started for maximum 30
seconds. If the capacity slide is still higher than a 5% position, an Oil log error shutdown will be issued,
and the compressor will not start. If the capacity slide is lower than 5%, the compressor is allowed to
start.
Before start-up, UniSAB III will also check the oil level and temperature in the oil separator. If the oil level
is too low, an Oil system error alarm will be issued and compressor state will be set to Pause. No signal
from the oil level switch during operation will result in shutdown after a delay of 30 seconds.
If the oil temperature is lower than the set limits, a Low oil separator tempalarm or shutdown will be is-
sued. The limits for oil separator temperature can be set in the menu Control values/Oil/Separator temp/
Limits. If the oil level switch is active and the separator temperature is above the shutdown limit, the
compressor will start.
Before start-up, and if the configuration parameter Suction press. grad. is enabled, UniSAB III will check
if the Suction superheat is lower than the Suction pressure gradient reset parameter. If this is the case,
the compressor will not start. A Low suction superheat alarm will be issued, and compressor state will
be set to Pause.
Running
After the starting sequence and during normal running operation, the slide capacity must be higher than
the minimum capacity, i.e. the configuration limit Manual zero.
For compressors without VSD, Manual zero is default 30% and for compressors with VSD drive, Manual
zero is calculated automatically.
Alarm surveillance
Low oil pressure
High filter diff. pressure
Low superheat
High superheat
Low/high oil temperature
The delayed alarms are described in section 6.5 Timers.
Stopping sequence
Under normal running conditions, the SAB 273 S compressor will stop when it is under 5% above its
minimum capacity, i.e. the configuration limit Manual zero.
Engineering manual - UniSAB III 1.10.8
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