Sequence Of Operation - Perishable Mode Heating; Sequence Of Operation - Frozen Mode Cooling; Figure 5.6 Perishable Mode Heating - Carrier 69NT40-541-001 Operation And Service

5.10.2

Sequence of Operation - Perishable Mode Heating

The unit will heat only when in the Perishable Mode, relay TH is electronically locked out when in the
Frozen Mode.
a. If the air temperature decreases 0.5°C (0.9°F) below set point, the system enters the heating mode. (See
Figure 5.3). The controller closes contacts TH (see
nation thermostat (HTT) to energize the heaters (HR). The HEAT light is also illuminated. The evaporator
fans continue to run to circulate air throughout the container.
b. When the temperature rises to 0.2°C (0.4°F) below set point, contact TH opens to de-energize the heaters. The
HEAT light is also de-energized. The evaporator fans continue to run to circulate air throughout the container.
c. A safety heater termination thermostat (HTT), attached to an evaporator coil support, will open the heating
circuit if overheating occurs.
5.10.3

Sequence of Operation - Frozen Mode Cooling

1. In the Frozen Mode of operation the evaporator motors run in low speed.
2. In low temperature ambients the condenser fan will be cycled by the controller to maintain proper con-
densing pressure.
a. With supply air temperature above set point and de creasing, the unit will be cooling with the condenser fan
motor (CF), compressor motor (CH), evaporator fan motors (ES) energized and the COOL light illuminated.
(Figure 5.7.)
b. When the air temperature decreases to a predetermined tolerance above set point, the in-range light is illu-
minated.
NOTE

Figure 5.6 Perishable Mode Heating

ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
NOTE
5–11
Figure 5.6) to allow power flow through the heat termi-
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER
T-316