3.3.17 SAB 120 and 151 without oil pump
The compressors are equipped with capacity slide and automatic Vi-control. The Vi is control-
led in three steps. If the compressor is equipped with a frequency converter (VSD) see sub-
section 6.4.1. Drive, 6: Rotatune for additional set-up of Unisab III. The compressor has no
oil pump.
Starting sequence
When the compressor has received starting permission, Unisab III will check whether the ca-
pacity slide is in minimum position. If the capacity slide is higher than 5% position, the sole-
noid valve for decreasing capacity slide position will be activated for maximum 300 seconds.
If the capacity slide is still higher than 5% position, a Capacity error shutdown will be issued
and the compressor will not start. If the capacity slide is lower than 5% position the compres-
sor 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. 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 temp alarm or shutdown
will be issued. 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.
Alarm surveillance
During start the following alarms are delayed:
Low oil pressure 45 sec.
High filter diff. pressure 600 sec.
Low superheat 300 sec.
High superheat 300 sec.
Low/high oil temperature 300 sec.
The delayed alarms are described in section 6.5. Timers.
Stopping sequence
When a SAB 120 and 151 compressor stops, Unisab III will attempt to move the capacity slide
below 5% position. The solenoid valve for decreasing capacity slide position is activated for
maximum 300 seconds. If the capacity slide is not below 5% within the 300 seconds a Ca-
pacity error shutdown will be issued.
Vi ratio regulation
Unisab III regulates the Vi ratio in three steps according to the actual pressure ratio. Before
switching from one Vi-step to another, the actual Vi ratio for the compressor must have been
present for at least the time indicated in timer 34 Vi-pause (60 seconds). Otherwise the
change of the Vi step will be cancelled. The Vi-step stays in volume ratio 2.2 (0.0%) until the
compressor capacity is higher than 40%.
Compressor control and surveillance
Engineering manual - Unisab III 1.10
001930 en 2014.09
107/319
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