T-340
4–10
Figure 4.8 Controller Operation - Frozen Mode
4.3.17
Frozen “Heat” Mode
If the temperature drops 10°C (18°F) below set point, the unit will transition to the frozen “heating” mode. The evap
-
orator 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 temperature rises back to the transition point.
4.3.18
Frozen Economy Mode
In order to activate Frozen Economy Mode, 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 (4°F). 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 (0.4°F), the unit will restart the refrigeration system and continue to
cool until the off-cycle temperature criteria are met. If the control temperature is less than the frozen set point
+0.2°C (0.4°F) the unit will turn off the evaporator fans and restart another 60 minute off-cycle.
4.3.19
Frozen Mode Cooling - Sequence of Operation
a. When the return air temperature is above set point and decreasing, the unit will transition to economized
cooling with the condenser fan motor (CF), compressor motor (CH), economizer solenoid valve (ESV), low
speed evaporator fan motors (ES) energized and the white COOL light illuminated (see
).
Controller Set Point at or BELOW
−10
°
C (+14
°
F),
or −5
°
C (+23
°
F) optionally
−.20
°
C
+.20
°
C
Air Circulation
Cooling,
Economized
Set Point
+2.5
°
C
(+4.5
°
F)
Frozen Mode
Falling
Temperature
Rising
Temperature