Temperature Control - Frozen Mode; Frozen Mode - Conventional; Frozen Mode - Economy; Controller Alarms - Carrier 69NT40-541-001 Operation And Service

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.
4.3.12

Temperature Control - Frozen Mode

With configuration variable CnF26 set to -10°C the frozen mode of operation is active with set points at or below -
10°C (+14°F). With the variable set to -5°C, the frozen mode is active at or below -5°C (+23°F).
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.
4.3.13

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 fact to greatly improve the energy efficiency of the unit. Tempera-
ture control in the frozen range is accomplished by cycling the compressor on and off as the load demand requires.
The unit will operate in the conventional frozen mode when the controller set point is at or below the frozen range
and function code CD34 is set to "OFF".
If the return air temperature in the container drops 0.2°C (0.4°F) below the set point, the compressor is cycled off.
When the temperature is greater than 0.2°C (0.4°F) above the set point and the three minute time delay has been
met, the compressor will restart. The unit will always operate at full capacity, and the suction modulation valve will
open as allowed by current and pressure limiting.
On start up of the unit, SMV will reset to a known open position. This is accomplished by assuming the
valve was fully open, driving it fully closed, resetting the percentage open to zero, then opening to a
known 21% staging position.
To prevent rapid cycling of the compressor, a three minute compressor off time must be satisfied before the com-
pressor will restart. Under a condition of rapidly changing return air temperature, the time delay may allow the
return air temperature to rise slightly above set point temperature before the compressor can restart.
4.3.14

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 per-
form 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 -2°C. 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 +0.2°C., the unit will restart the refrigeration sys-
tem and continue to cool until the previously mentioned off-cycle temperature criteria are met. If the control tempera-
ture is less than the set point +0.2°C, the unit will turn off the evaporator fans and restart another 60 minute off-cycle.
4.4

CONTROLLER ALARMS

Alarm display is an independent controller software function. If an operating parameter is outside of expected
range or a components does not return the correct signals back to the controller an alarm is generated. A listing of
the alarms is provided in
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 compressor on
line. An example is alarm code "LO", (low main voltage), when a voltage drop of over 25% occurs, an indication is
given on the display, but the unit will continue to run.
An alarm is indicated by flashing an alarm code on the display panel, and for some alarms, by the alarm light illuminating.
T-316
Table 4–6.
NOTE
4–8