Service manual

T -318
3-- 4
To access the function codes, perform the following:
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 ex-
tend 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 above -5 C (+23 F). Refer to Table 3-4, page
3--13.
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 Evaporator Fan Operation
Opening of an evaporator fan internal protector will shut
down a unit with Normal Evaporator Fan Operation.
(CnF32 set to 2EFO). On units equipped with Single
Evaporator Fan Capability (CnF32 set to 1EFO),
additional relays are installed to allow the unit to
continue to operate on a single fan (refer to Table 3-4,
page 3--13).
3.3.3 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 three 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 three 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. Defrost interval time is not accumulated in
any mode until the defrost termination sensor reads less
than 10 degrees C (50 degrees F).
3.3.4 Failure Action
Function code Cd29 may be operator set to allow
continued operation in the event the control sensors are
reading out of range. The factory default is full system
shutdown (refer to Table 3-5, page 3--14).
3.3.5 Generator Protection
Function codes Cd31 and Cd32 may be operator set to
control start-up sequence of multiple units and
operating current draw. The factory default allows on
demand starting of units and full current draw (refer to
Table 3-5, page 3--14).
3.3.6 Condenser Pressure Control
When configuration variable CnF14 is set to “In,” the
condenser pressure control logic is activated to
maintain discharge pressures above 130 psig in low
temperature ambients. The logic turns the condenser
fan on or off in accordance with the condenser pressure
transducer reading (refer to Table 3-4, page 3--13.) The
function is enabled when the following conditions are
met:
1. The ambient sensor reading is less than or equal to
27 C (80 F), and
2. V oltage/Frequency ratio is less than or equal to 8.38.
When the above conditions are met, either pressures or
timers may dictate a change of state from OFF to ON or
ON to OFF. If the condenser fan is OFF, it will be
energized if saturated condensing pressure is greater
than 200 psig OR if the condenser fan has been OFF for
a variable time period of up to 60 seconds depending on
the ambient temperature. As the ambient temperature
increases, the amount of time that the condenser fan is
energized will correspondingly increase towards the
maximum.
If the condenser fan is ON, it will de-energize only if the
saturated condensing pressure is less than 130 psig
and the condenser fan has been running for a minimum
of thirty seconds depending on the ambient
temperature.
3.3.7 Arctic Mode
With arctic mode enabled (configuration variable CnF29
set to “In”), there will be a 30-minute time delay at
startup if the ambient is colder than -10.0 C (14 F). When
the START/STOP switch is placed in the “I” (ON)
position, the controller will energize the compressor
crankcase heater. Operation of the heater will warm the
oil and boil off any liquid refrigerant that may be present
in the crankcase.
If Pre-Trip is initiated during the 30 minute time period,
Pre-Trip will be allowed to run normally. Once Pre-Trip is
over , the controller will revert to its normal control mode
logic (refer to Table 3-4, page 3--13).