Compressor Control - User Functions; External Starting Permission - Immediate Stop; External Starting Permission - Normal Stop; Capacity Down Blocked - Johnson Controls SABROE UniSAB III Engineering Manual

Compressor control and surveillance
3.5

Compressor control - user functions

3.5.1

External starting permission - immediate stop

The input must be connected for the compressor to run in Manual, Auto or Remote. If this input is
opened during operation the compressor stops immediately.
When the input is open Stopped appears in the bottom line of the display.
3.5.2

External starting permission - normal stop

This input and External starting permission - immediate stop must be connected before the compressor
is going to start in Auto or Remote but it can be started in Manual mode.
If the input has not been connected, the display will show Stopped in the bottom line. If the input is
opened during operation, the compressor capacity will be decreased to minimum and the compressor
will stop on its Delay before stop timer.
In case the input Capacity down blocked is connected, the compressor will not reduce capacity once the
input External starting permission - normal stop is opened.
3.5.3

Capacity down blocked

This function is enabled in Setup/configuration/Plant/Cap down blocked.
When the compressor is in maximum capacity in Auto or Remote it can be locked in this state by closing
a digital input. See wiring diagrams. The input overrules External starting permission - normal stop.
If the compressor runs in limited operation (a limiting function is active), it will however reduce its ca-
pacity. When the state of operation is back to normal, the compressor will return to full load. See also 3.2
Limiting functions.
If the input is connected while the compressor is ready to start in Auto or Remote, the compressor will
be started by force irrespective of actual regulator settings.
In case the chiller and flow condenser function have both been configured, it will not be possible to use
the capacity blocked function. See section 3.6 Compressor control - chiller functions.
3.5.4

Power management system (PMS)

This function works in Manual, Auto or Remote operation. It is a kind of "an agreement to start" system,
consisting of one digital output PMS Request, which is set when the compressor should start, and a digi-
tal input PMS feedback. This input must be set before the timer PMS feedback expires in order for the
compressor to start.
The shutdown PMS error is activated if the input PMS feedback has not been set before the timer PMS
feedback expires.
If the PMS feedback fixed is configured to No the feedback signal can be removed during operation with-
out stopping the compressor.
If the PMS feedback fixed is configured to Yes the feedback signal cannot be removed during operation
without stopping the compressor, having a PMS error shutdown.
3.5.5

Cold store function

This function is connected to the regulators for capacity regulation of the compressor. Usually, the com-
pressor is going to start in Auto or Remote/Multisab if the measured value is outside the neutral zone
and a capacity requirement exists.
If the Cold store function has been selected in the menu Compr. Control, the compressor will not start
until the measured value is outside the P Band. After this it will regulate normally in accordance with the
set point.
Example of cold store function: UniSAB III is set for suction pressure regulation with
Set point (Sp) = -40°C
Engineering manual - UniSAB III 1.10.8
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