6 – 7
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
Section 6
•
Compressor Control
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 de
fi
nes a method of “pump-
ing” down a chiller, which is to draw off refrigerant from
the chiller. This feature can be enabled or disabled from
this page, see Figure 6-8. If Pumpdown is enabled, this
feature will only function when the compressor is run-
ning in local Auto Mode and Control Mode Con
fi
gured is
Suction Pressure.
If Pumpdown Feature is enabled, and 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, Pumpdown setpoints are ig-
nored and the user is not allowed to edit Pumpdown
setpoints.
Stop Pressure:
• This setpoint de
fi
nes 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 opera-
tion. This button is active only when compressor is
in local Auto mode and Control Mode Con
fi
gured 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 Pumpdown feature is enabled, Pulldown check-
box is automatically grayed out. Similarly when Pulldown
feature is enabled, Pumpdown checkbox is automatically
grayed out and hence, the user will not be able to oper-
ate Pumpdown feature. This is done to keep Pumpdown
and Pulldown features mutually exclusive.
Pulldown Control
The Pulldown Control de
fi
nes a method of slowly pull-
ing the suction pressure down from a high value. This is
sometimes required on systems that have liquid recircu-
lation systems or on new building to prevent structural
damage by limiting the rate at which to build is cooled.
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