3--6
T-334
thermostat settings. (Refer to paragraph NO TAG.) The
temperature at which the defrost termination thermostat
will be considered “open” may be changed [in 0.1C
(0.2F) increments] to any value between 25.6C (78F)
and 4C (39.2F). The temperature at which the defrost
termination thermostat is considered closed for interval
timer start or demand defrost is 10C for “open” values
from 25.6C (78F) down to a 10C setting. For “open”
values lower than 10C, the “closed” values will decrease
to the same value as the “open” setting. Bulb mode is
terminated when:
1. Bulb mode code Cd35 is set to “Nor.”
2. Dehumidification code Cd33 is set to “Off.”
3. The user changes the set point to one that is in the
frozen range.
When bulb mode is disabled by any of the above, the
evaporator fan operation for dehumidification reverts to
“alt” and the DTS termination setting resets to the value
determined by controller configuration variable CnF41.
3.3.11 Perishable - System Pressure Regulation
In perishable mode, system pressures may need to be
regulated at ambient temperatures of 20C (68F) and
below. Once below this ambient temperature, the
condenser fan may cycle on and off based on limits
imposed for discharge pressure. For extremely cold
ambient temperatures, -18C (0F), heater cycling may
occur within normal system operation based on
discharge pressure limits. For ambient temperatures
below -29C (-20.2F) the SMV may regulate to a higher
percent opening based on discharge pressure output.
3.3.12 Temperature Control - Frozen Mode
With configuration variable CnF26 (Heat Lockout
Temperature) set to -10C the frozen mode of operation
is active with set points
at or below -10C (+14
F). With
the variable set to -5C, the frozen mode is active at or
below -5C (+23F).
When in the frozen mode the controller maintains the
return air temperature at set point, the RETURN
indicator light will be illuminated on the display module
and the default reading on the display window will be the
return air probe reading.
When the return air temperature enters the in-range
temperature tolerance as selected at function code
Cd30, the in-range light will energize.
3.3.13 Frozen Mode - Conventional
Frozen range cargos are not sensitive to minor
temperature changes. The method of temperature
control employed in this range takes advantage of this to
greatly improve the energy efficiency of the unit.
Temperature control in the frozen range is
accomplished by cycling the compressor on and off as
the load demand requires.
When cooling from a temperature that is more than 2.5C
(4.5F) above set point, the system will be in the frozen
pulldown mode. It will transition to 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
frozen steady state mode. (Economized operation with
maximum allowed suction modulating valve opening.)
When temperature drops to set point minus 0.2C and
the compressor has run for at least five minutes, the unit
will transition to the frozen 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 +0.2C, the unit will transition back
to the frozen steady state mode.
If the temperature drops 10C below set point, the unit
will transition to the frozen “heating” mode, in which the
evaporator fans are brought to high speed. The unit will
transition back to the frozen steady state mode when
the temperature rises back to the transition point.
3.3.14 Frozen Mode - Economy
In order to activate economy frozen mode operation, a
frozen set point temperature must be selected. The
economy mode is active when function code Cd34 is set
to “ON.” When economy mode frozen is active, the
system will perform normal frozen mode operations
except that the entire refrigeration system, excluding
the controller, will be turned off when the control
temperature is less than or equal to the set point -2C.
After an off-cycle period of 60 minutes, the unit will turn
on high speed evaporator fans for three minutes, and
then check the control temperature. If the control
temperature is greater than or equal to the set point
+0.2C, the unit will restart the refrigeration system and
continue to cool until the previously mentioned off-cycle
temperature criteria are met. If the control temperature
is less than the set point +0.2C, the unit will turn off the
evaporator fans and restart another 60 minute off-cycle.
3.3.15 Condenser Fan Switch Override
When configuration variable CnF15 (Discharge
Temperature Sensor) is set to “In” and CnF48
(Condenser Fan Switch Override) is set to “On” the
condenser fan switch override logic is activated. If
condenser cooling water pressure is sufficient to open
the water pressure switch (de-energizing the condenser
fan) when water flow or temperature conditions are not
maintaining discharge temperature the logic will
energize the condenser fan as follows:
1. If the discharge temperature switch reading is valid
and discharge temperature is greater than 115C
(240F), the condenser fan is energized.
2. When discharge temperature falls to 90.5C (195F)
the condenser fan is de-energized.
3. If the system is running on condenser fan override
and the high pressure switch opens twice, within a
seven minute period, the condenser fan is energized
and will remain energized until the system is power
cycled. Alarm 58 (Compressor High Pressure Safe-
ty) will be triggered.
3.4 CONTROLLER ALARMS
Alarm display is an independent controller software
function. If an operating parameter is outside of
expected range or a component does not return the
correct signals back to the controller an alarm is
generated. A listing of the alarms is provided in
Table 3--6, page 3--20.
The alarm philosophy balances the protection of the
refrigeration unit and that of the refrigerated cargo. The
action taken when an error is detected always considers
the survival of the cargo. Rechecks are made to confirm
that an error actually exists.
Some alarms requiring compressor shutdown have
time delays before and after to try to keep the
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