Perishable Heating; Perishable Pulldown; Perishable Dehumidification; Figure 4.5 Controller Operation - Perishable Mode - Carrier 69NT40-561-399 Operation And Service Manual

4.3.6

Perishable Heating

When it is necessary to raise the control temperature, the system will enter Perishable Heating Mode. If the tem-
perature drops to 0.5°C (0.9°F) below set point, the unit will transition to Perishable Heating Mode, and the heaters
will be energized. The unit will transition back to Perishable Idle Mode when the temperature rises to 0.2°C
(0.36°F) below the set point, and the heaters will de-energize.
4.3.7

Perishable Pulldown

When the system is in Perishable Pulldown Mode, the highest priority is given to bringing the container down to set
point. When cooling from a temperature that is more than 2.5°C (4.5°F) above set point, the system will be in per-
ishable pulldown mode in economized operation. However, pressure and current limit functions may restrict the
valves if either exceeds the preset value.
Once set point is reached, the unit will transition to perishable steady state mode. This results in unloaded opera-
tion by cycling the DLV and DUV to limit capacity and maintain steady temperature control.
Perishable Mode
Controller Set Point ABOVE 10 C (+14 F),
or 5 C (+23 F) optionally
Set
Point
.20 C Air Circulation
.50 C
Falling
Temperature
4.3.8

Perishable Dehumidification

Dehumidification is provided to reduce the humidity levels inside the container, the dehumidification set point range
is from 50% to 95%. Dehumidification is activated when a humidity value is set at Cd33. During dehumidification
operation the condenser fan speed is fixed in high speed. The yellow SUPPLY LED will flash ON and OFF every
second to indicate that dehumidification is active. Once dehumidification is active and the following conditions are
satisfied, the controller will activate the heat relay to begin dehumidification.
• The humidity sensor reading is above the humidity set point (Cd33).
• The unit is in perishable steady state and supply air temperature is less than 0.25°C (0.45°F) above set point.
• The heater debounce timer (three minutes) has timed out.
• Heater termination thermostat (HTT) is closed.
T-365

Figure 4.5 Controller Operation - Perishable Mode

Cooling,
Unloaded
+.20 C
.25 C
Heating
Rising
Temperature
Pull Down
(Only Applicable to Perishable Mode)
Controller Set Point ABOVE 10 C (+14 F),
or 5 C (+23 F) optionally
Cooling,
Economized
Cooling,
Unloaded
.20 C
Air Circulation
.50 C
Heating
4–6
+2.5 C
(+4.5 F)
Set
Point
.20 C