6 – 9
Section 6
•
Compressor Control
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
Oil Restriction Setpoint:
• This is the compressor VFD RPM setpoint used for
turning ON/OFF the Oil Solenoid Digital Output. Oil
Solenoid Digital Output is turned ON when the com-
pressor is Running, Warm up Timer is Lapsed and
Compressor VFD RPM goes below this setpoint.
Oil Restriction Differential:
• This is the differential around Oil Restriction Setpoint.
Oil Restriction Offset:
• This is the differential offset around Oil Restriction
Setpoint. For example, if Oil Restriction Setpoint is
set to 1800 RPM and Oil Restriction Offset is set to
5 RPM, then as Compressor VFD RPM decreases to
1795 RPM, then Oil Solenoid Digital Output will be
turned ON. If Compressor VFD RPM increases to 1805
RPM, then Oil Solenoid Digital Output will be turned
OFF.
Pumpdown Control
NOTE
For use of compressor control screen - page 4, see
Cool Compression Control in Section 25.
The Pumpdown Control defines a method of “pumping”
down a chiller, which is to draw off refrigerant from it.
This feature can be enabled or disabled from this page,
see Figure 6-11. If Pumpdown is enabled, this feature
will only function when the compressor is running in lo-
cal Auto Mode and Control Mode Configured is Suction
Pressure.
When Pumpdown Control is running, a status icon will
appear on the bottom left corner of the main screen to
make the user aware of it.
If the Pumpdown Feature is enabled, then;
• The Auto-cycle functionality is ignored. Pumpdown
mode will cause the compressor to cycle off via the
Pumpdown Stop Pressure setpoint. Normally, the
Pumpdown Stop Pressure setpoint will be set lower
than the Auto-cycle Stop setpoint. Therefore, as the
suction pressure is pulled down, the compressor is
prevented from shutting down prematurely via the
Auto-cycle Stop setpoint by automatically ignoring
the Auto-cycle feature.
• The compressor will be placed into “Stop” mode af-
ter the suction pressure is equal to, or goes below the
Pumpdown Stop Pressure.
Pumpdown:
• This checkbox enables the Pumpdown feature. If this
box is unchecked, the Pumpdown setpoints are ig-
nored and the user is not allowed to edit them.
Stop Pressure:
•
This setpoint defines the suction pressure value at
which the compressor will cycle off. Normally, this
setpoint is set below the Suction Pressure Auto-cycle
Stop Pressure setpoint.
Stop Delay:
• This setpoint delays the compressor from stopping
when the suction pressure is equal to or less than the
Stop Pressure.
Min Slide Position:
• The minimum capacity slide is the setpoint that
the compressor is allowed to run at. By forcing the
compressor capacity to operate at a value above
minimum, we insure that the suction pressure will be
pulled down to the Stop Pressure setpoint.
Pumpdown Operation (Run/Stop):
• This button starts/stops the Pumpdown operation.
This button is active only when compressor is in lo-
cal Auto mode and the Control Mode configured is
Suction Pressure. This button will display “Run” when
Pumpdown operation has not started or stopped,
while button will display “Stop” when Pumpdown op-
eration is running.
When the Pumpdown feature is enabled, the Pulldown
checkbox is automatically grayed out. Similarly when
Pulldown feature is enabled, the Pumpdown checkbox
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