Carrier 69NT40-541-300, Operation And Service, Page: 40 / 152

T-318 3 − 8
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Controller Set Point at or BELOW − 10 ° C (+14 ° F),
or − 5 ° C (+23 ° F) optionally
− .20 ° C
+.20 ° C
Air Circulation
Cooling
Set Point
+2.5
°
C
(+4.5 ° F)
Frozen Mode
Falling
Temperature
Rising
Temperature
Figure 3-8 Controller Operation − Frozen Mode
3.3.13 Frozen Idle Mode
When temperature drops to set point minus 0.2 C
(0.4 F) 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 +0.2 C, (0.4 F) the
unit will transition back to the frozen steady state mode.
NOTE
On start up of the unit, SMV will reset to a known
open position. This is accomplished by assum-
ing 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
compressor 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.
3.3.14 Frozen “Heat” Mode
If the temperature drops 10 C below set point, the unit
will transition to the frozen “heating” mode. The evapo-
rator fans are brought to high speed, and the heat from
the fans is circulated through the container. The unit will
transition back to frozen steady state when the tempera-
ture rises back to the transition point.
3.3.15 Frozen Economy Mode
In order to activate economy frozen mode operation, a
frozen set point temperature must be selected, and
Cd34 (Economy Mode) set to “ON.” When economy
mode 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 -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 frozen set
point +0.2
°
C, 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 frozen set point +0.2 ° C, the
unit will turn off the evaporator fans and restart another
60 minute off-cycle.