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Unit Description
35
Operating Modes
NOTE: See Controller chapter for complete
sequence of operation.
A sequence start of the required loads occurs
during initial start-up of the unit and when a
control mode shift requires the compressors to
start. As the controller relays and unit loads
energize, the controller LCD display shows the
setpoint temperature. The controller LED display
shows the controlling air sensor temperature. The
controlling sensor is determined by the setpoint
temperature:
With a Setpoint of -9.9 C (14.1 F) and above the
Supply Air Temperature is the controlling sensor.
With a setpoint of -10 C (14 F) and below the
Return Air Temperature is the controlling sensor.
The controller uses a complex proportional-
integral derivative (PID) algorithm to provide
accurate temperature control in direct response to
load demand. Therefore it is difficult to predict
which operating mode the unit should be in by
comparing the setpoint to the return or supply air
temperature. The unit operates in either the Fresh
(Chill) or Frozen mode. Chill to Frozen mode
transition point is -10 C (14 F).
NOTE: If the compressor has been OFF for
more than 8 hours, or the unit has been on heat
or defrost; the controller performs a compressor
sequence start.
Chill Loads: Controller Setpoint at
-9.9 C (14.1 F) or Above
Temperature control by the controller is based on
the supply air sensor temperature, the setpoint, the
modulation temperature range and the pull-down
rate. The evaporator fans operate in high speed.
•
Cool with Modulation (down to setpoint)
•
Null (compressor and condenser fan stops,
evaporator fans operate)
•
Heat (resistance heaters on, evaporator fans
operate)
•
Defrost (resistance heaters on, evaporator fans
stop)
NOTE: If the Economy Mode is set to ON,
the evaporator fans operate on low speed at
set-points of -9.9 C (14.1 F) and above
whenever the container temperature is
In-range.
Frozen Loads: Controller Setpoint
at -10 C (14 F) or Below
Temperature control by the controller is based on
the return air sensor temperature. The evaporator
fans operate continuously on low speed (except
during defrost).
•
Cool (down to 1 C [1.8 F] below setpoint)
•
Null (compressor and condenser fan stops,
evaporator fans operate)
•
Defrost (resistance heaters on, evaporator fans
stop)
NOTE: If the Economy Mode is set to ON,
the evaporator fans stop when the unit shifts
to Null. The controller automatically starts
and operates the evaporator fans on low
speed for 5 minutes every 45 minutes while
the unit remains in Null.
Summary of Contents for CRR-40 119
Page 4: ......
Page 16: ...Safety Precautions 16...
Page 18: ...Service Guide 18...
Page 20: ...Model Features 20...
Page 32: ...Specifications 32...
Page 120: ...MP 3000a Controller 120...
Page 160: ...Wiring and Schematic Diagrams Index 160...
Page 161: ...161 MPC2000 Wiring Schematic...
Page 162: ...162 MPC2000 High Voltage Wiring Diagram...
Page 163: ...163 MPC2000 Low Voltage Wiring Diagram...
Page 164: ...164 MPC2000 WCC Wiring Schematic...