4–5
T-340
Operational software responds to various inputs. These inputs come from the temperature and pressure sensors,
the temperature set point, the settings of the configuration variables and the function code assignments. The action
taken by the operational software changes as the input values change. Overall interaction of the inputs is described
as a “mode” of operation. The modes of operation include perishable (chill) mode and frozen mode. Descriptions of
the controller interaction and modes of operation are provided in the following sub-paragraphs.
4.3.1
Start up - Compressor Phase Sequence
At start up, the controller logic checks for proper phase sequencing and compressor rotation. If incorrect sequenc
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ing is causing the compressor and three-phase evaporator fan motors to rotate in the wrong direction, the controller
will energize or de-energize relay TCP as required. Relay TCP will switch its contacts, energizing or de-energizing
relays PA and PB. Relay PA is wired to energize the circuits on L1, L2 and L3. Relay PB is wired to energize the cir
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cuits on L3, L2, and L1, thus providing reverse rotation.
4.3.2
Start up - Compressor Bump Start
At start up, the controller logic will initiate a compressor bump start procedure to clear liquid refrigerant from the
compressor. If suction and discharge pressures have equalized, the compressor will perform three compressor
bump starts. A compressor bump start may also occur after a defrost cycle has been completed.
During Bump Start, the EEV will close. Relays TS, TQ, TN, TE, and TV will be de-energized (opened). The result of this
action will close the ESV and shut all fans off. The compressor will start for 1 second, then pause for five seconds. This
sequence will be repeated two more times. After the final bump start the unit will pre-position the EEV to the correct
starting position, pause and start up.
4.3.3
Perishable Mode Temperature Control
In Perishable Mode, the controller maintains the supply air temperature at set point, the SUPPLY indicator light is
illuminated and the default reading on the display window is the supply temperature sensor reading.
When the supply air temperature enters the in-range temperature tolerance (Cd30), the green IN-RANGE light will
energize.
When CnF26 (Heat Lockout Temperature) is set to -10°C, perishable mode is active with set points
above -10°C
(+14°F)
. When CnF26 is set to -5°C, perishable mode is active with set points
above -5°C (+23°F)
.
4.3.4
Perishable Pulldown
When the system is in Perishable Pulldown Mode, the highest priority is given to bringing the container down to set
point. When cooling from a temperature that is more than 2.5°C (4.5°F) above set point, the system will be in perish
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able pulldown mode in economized operation.
However, pressure and current limit functions may restrict the valve if either exceeds the preset value.
4.3.5
Perishable Steady State
Perishable Steady State is used to maintain the control temperature near a setpoint that is above the heat lockout
temperature.
Once set point is reached, the unit will transition to perishable steady state mode. This results in unloaded opera
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tion by cycling the DUV to limit capacity and maintain steady temperature control.
The unit is capable of maintaining supply air temperature to /-0.2°C (+/-0.36°F) of set point. Supply air tem
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perature is controlled by positioning of the electronic expansion valve (EEV), cycling of the digital unloader valve
(DUV), cycling of the compressor, and cycling of the heaters.
4.3.6
Perishable Idle, Air Circulation
Perishable Idle Mode is used when it is unnecessary to run the compressor to maintain control temperature. If the
controller has determined that cooling is not required or the controller logic determines suction pressure is at the
low pressure limit, the unit will transition to Perishable Idle Mode. During Perishable Idle Mode, the compressor is
turned off, but the evaporator fans continue to run to circulate air throughout the container. If temperature rises
+0.2°C above set point, the unit will transition back to perishable steady state.
4.3.7
Perishable Heating
When it is necessary to raise the control temperature, the system will enter Perishable Heating Mode. If the tem
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perature drops to 0.5°C (0.9°F) below set point, the unit will transition to Perishable Heating Mode, and the heaters
will be energized. The unit will transition back to Perishable Idle Mode when the temperature rises to 0.2°C (0.4°F)
below the set point, and the heaters will de-energize.
