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4.2.2
Operational Software (Cd Function
Codes)
The operational software is the actual operation pro-
gramming of the controller which activates or deacti-
vates components in accordance with current unit
operation conditions and selected modes of operation.
The programming is divided into function codes. Some
of the codes are read only, while the remaining codes
may be user configured. The value of the user configu-
rable codes can be assigned in accordance with user
desired mode of operation. A list of the function codes
is provided in
Table
To access the function codes:
a. Press CODE SELECT, then press an arrow key
until the left window displays the desired func-
tion code.
b. The right window will display the selected func-
tion code value for five seconds before returning
to the default display mode.
c. If additional time is required, pressing the
ENTER key will extend the display time to 30
seconds.
4.3
MODES OF OPERATION
General operation sequences for cooling, heating, and
defrost are provided in the following sub-paragraphs.
Schematic representation of controller actions are pro-
vided in
Figure 4.5
Operational software responds to various inputs.
These inputs come from the temperature sensors and
pressure transducers, 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 con-
troller interaction and modes of operation are provided
in the following sub paragraphs.
4.3.1
Perishable Mode Temperature Control
The unit is capable of maintaining supply air tempera-
ture to within +/- 0.25°C (+/- 0.5°F) of set point. Supply
air temperature is controlled by positioning of the suc-
tion modulation valve (SMV), cycling of the compres-
sor, and cycling of the heaters.
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.
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Figure
4.8.
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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).
4.3.2
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 5°C (9°F) above set point, the system will be
in Perishable Pulldown Mode, and the SMV will open to
reduce the pulldown time.
However, pressure and current limit functions may
restrict the valve if either exceeds the preset limits.
4.3.3
Perishable Steady State
Perishable Steady State is used to maintain the control
temperature near a setpoint that is above the heat lock-
out temperature.
The operational software is designed so the SMV will
begin to close as the set point is reached. The SMV will
continue to close and restrict refrigerant flow until the
capacity of the unit and the load are balanced.
If the temperature drops below the set point, the com-
pressor will remain running for a few minutes. This is to
accommodate any initial undershoot which might
occur. After this time has expired and the temperature
is 0.2°C (0.36°F) or greater below the set point, the
compressor will be turned OFF.
If the temperature drops to 0.5°C (0.9°F) below set
point, the heaters will be energized. The heaters will
de-energize when the temperature rises to 0.2°C
(0.36°F) below the set point. The compressor will not
restart until the temperature rises to 0.2°C (0.36°F)
above the set point and three minutes have elapsed
since the last compressor turn off.
4.3.4
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 pres-
sure 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.
4.3.5
Perishable Heating
When it is necessary to raise the control temperature,
the system will enter Perishable Heating Mode. If the
temperature 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 (0.36°F) below the set point, and the heaters will
de−energize.
4–4
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