3-4
T-296
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, 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
Function code Cd27 may be operator set to initiate
defrost at intervals of 3, 6, 9, 12 or 24 hours. The factory
default is 12 hours. (Refer to Table 3-5, page 3-14).
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)
2. Voltage/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 sixty 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.
3.3.8 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 pulling down from a temperature that is more than
5
_
C (9
_
F) above set point, the SMV will open to reduce
the pulldown time. However, pressure and current limit
functions may restrict the valve, if either exceeds the
preset value.
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.
Downloaded from
