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a. Press the CODE SELECT key, then press an arrow
key until the left window displays the desired code
number.
b. The right window will display the value of this item for
five seconds before returning to the normal display
mode.
c. If a longer time is desired, press the ENTER key to
extend the time to 30 seconds.
3.3 MODES OF OPERATION
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 Temperature Control - - Perishable Mode
With configuration variable CnF26 (Heat Lockout
Temperature) set to --10_C the perishable mode of
operation is active with set points above - -10_C (+14_F).
With the variable set to --5_C, the perishable mode is
active below - -5 _ C (+23 _ F). Refer to Table 3-4.
When in the perishable mode the controller maintains
the supply air temperature at set point, the SUPPLY
indicator light will be illuminated on the display module
and the default reading on the display window will be the
supply temperature sensor reading.
When the supply air temperature enters the in-range
temperature tolerance (as selected at function code
Cd30), the in-range light will energize.
3.3.2 Defrost Interval
Controller function code Cd27 sets two modes for
defrost initiation, either user--selected timed intervals or
automatic control. The user--selected values are 3, 6, 9,
12, or 24 hours and the factory default for the timed
interval is 12 hours (some units may be configured to
allow defrost to be disabled altogether; in this case a
user--selected value of OFF will be available). Refer to
Table 3-5.
In perishable mode, perishable--pulldown mode, or
frozen--pulldown mode, automatic defrost starts with an
initial defrost set to 3 hours and then adjusts the interval
to the next defrost based on the accumulation of ice on
the evaporator coil. In this way, defrosts are scheduled
to occur only when necessary.
Once setpoint has been reached in frozen operation, the
automatic selection will set the time interval to 12 hours
for the first two defrosts once the return probe is reading
below the frozen setpoint and then adjust to 24 hours
thereafter.
All defrost interval times reflect the number of
compressor runtime hours since the last defrost de--ice
cycle.
The minimum defrost interval under the
automatic setting is 3 hours while the maximum is 24. In
frozen mode the amount of wall--clock time necessary to
accumulate a given amount of defrost interval time will
exceed the defrost interval time by a factor of two to
three depending on the compressor duty--cycle.
T-320
Defrost interval time is not accumulated in any mode
until the defrost termination sensor reads less than
10_C (50_F).
3.3.3 Failure Action
Function code Cd29 may be operator set to allow
continued operation in the event that all of the control
sensors are reading out of range. The factory default is
full system shutdown. Refer to Table 3-5.
3.3.4 Generator Protection
Function codes Cd31(Stagger Start, Offset Time) and
Cd32 (Current Limit) may be operator set to control start
up sequence of multiple units and operating current
draw. The factory default allows on demand starting (no
delay) of units and normal current draw. Refer to
Table 3-5.
3.3.5 Compressor High Temperature, Low Pres-
sure Protection.
The
controller
monitors
temperature and suction pressure. If discharge
pressure rises above the allowed limit or suction
pressure falls below the allowed limit the compressor
will be cycled off on a three minute timer. Condenser and
evaporator fans continue to operate during the
compressor off cycle.
3.3.6 Perishable Mode - - Conventional
The unit is capable of maintaining supply air
temperature to within ¦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.
When cooling from a temperature that is more than
2.5_C (4.5_F) above set point, the system will be in the
perishable pull down mode. It will be in economized
operation with a target SMV position of 100% open.
However, pressure and current limit functions may
restrict the valve, if either exceeds the preset value.
Once set point is reached, the unit will transition to the
perishable steady state mode. This results in unloaded
operation with some restriction of the SMV. The SMV
will continue to close and restrict refrigerant flow until the
capacity of the unit and the load are balanced.
If the SMV is at minimum modulation, 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 the perishable idle mode.
The compressor is turned off and the evaporator fans
continue to run to circulate air throughout the container.
If temperature rises above set point +0.2_C, the unit will
transition back to the perishable steady state mode
If the temperature drops to 0.5_C (0.9_F) below set
point, the unit will transition to the perishable heating
mode and the heaters will be energized . The unit will
transition back to the perishable idle mode when the
temperature rises to 0.2_C (0.4_F) below the set point
and the heaters will de-energize
3.3.7 Perishable Mode - - Economy
The economy mode is an extension of the conventional
mode. The mode is activated when the setting of
function code Cd34 is "ON". Economy mode is provided
for power saving purposes. Economy mode could be
utilized in the transportation of temperature tolerant
cargo or non-respiration items which do not require high
airflow for removing respiration heat. There is no active
3-4
compressor
discharge
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