T-318
3
−
4
3.2.2 Operational Software (Cd Function Codes)
The operational software is the actual operation
programming of the controller, which activates or
deactivates 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
configurable codes can be assigned in accordance with
user desired mode of operation. A list of the function
codes is provided in Table 3-5.
To access the function codes:
a. Press the CODE SELECT key, then press an arrow
key until the left window displays the desired function
code.
b. The right window will display the selected function
code value for five seconds before returning to the de-
fault display mode.
c. If additional time is required, pressing the ENTER key
will extend the display time to 30 seconds.
3.3 MODES OF OPERATION
General operation sequences for cooling, heating, and
defrost are provided in the following subparagraphs.
Schematic representation of controller actions are
provided in Figure 3-5 and Figure 3-8.
The operational software responds to various inputs.
These inputs come from the temperature and pressure
sensors, the temperature set point, the settings of the
the configuration variables, and the function code
assignments. The action taken by the operational
software will change if any one of the inputs changes.
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.
3.3.1 Perishable Mode Temperature Control
The unit is capable of maintaining supply air
temperature to /- 0.25
C (+/- 0.5
F) of set point.
Supply air temperature is controlled by positioning of the
suction modulation valve (SMV), cycling of the
compressor, 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 win-
dow 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
).
3.3.2 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 re-
duce the pulldown time.
However, pressure and current limit functions may re-
strict the valve if either exceeds the preset value.
3.3.3 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
compressor 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 (0.4
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
(0.4
F) below the set point. The compressor will not
restart until the temperature rises to 0.2
C (0.4
F)
above the set point and three minutes have elapsed
since the last compressor turn off.
3.3.4 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 pressure is at
the low pressure limit, the unit will transition to Perish-
able Idle Mode. During Perishable Idle Mode, the com-
pressor is turned off, but the evaporator fans continue to
run to circulate air throughout the container. If temperat-
ure rises +0.2
C above set point, the unit will transition
back to perishable steady state.
3.3.5 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 (0.4
F) below the set point, and the heaters will
de
−
energize.