5–11
T-316
5.10.2
Sequence of Operation - Perishable Mode Heating
NOTE
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
). The controller closes contacts TH (see
) to allow power flow through the heat termi-
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.
Figure 5.6 Perishable Mode Heating
5.10.3
Sequence of Operation - Frozen Mode Cooling
NOTE
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.
(
.)
b. When the air temperature decreases to a predetermined tolerance above set point, the in-range light is illu-
minated.
CONTROL TRANSFORMER
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
SIGNAL TO
CONTROLLER
ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
Содержание 69NT40-541-001
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