Sequence Of Operation - Perishable Mode Cooling; Figure 5.5 Perishable Mode Cooling - Carrier 69NT40-541-001 Operation And Service

5.10.1

Sequence of Operation - Perishable Mode Cooling

In the Conventional Perishable Mode of operation the evaporator motors run in high speed. In the
Economy Perishable Mode the fan speed is varied.
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 decreasing, the unit will be cooling with the condenser fan
motor (CF), compressor motor (CH), evaporator fan motors (EF) energized and the COOL light illuminated.
(See Figure 5.5.)
b. When the air temperature decreases to a predetermined tolerance above set point, the in-range light is illu-
minated.
c. As the air temperature continues to fall, modulating cooling starts at approximately 2.5°C (4.5°F) above set
point. (See Figure
d. The controller monitors the supply air. Once the sup ply air falls below set point and 0% SMV position is
reached, the controller periodically records the supply air temperature, set point and time. A calculation is
then performed by subtracting the set point reading from the supply air and multiplying the result by the time
reading. The result is negative number.
e. When the calculation reaches -250, contacts TC and TN are opened to de-energize compressor and con
denser fan motors. The cool light is also de-energized.
f. The evaporator fan motors continue to run to circulate air throughout the container. The in-range light
remains illuminated as long as the supply air is within tolerance of set point.
g. When the supply air temperature increases to 0.2°C (0.4°F) above set point and the three minute off time
has elapsed, relays TC and TN are energizes to re start the compressor and condenser fan motors. The
cool light is also illuminated.
T-316

Figure 5.5 Perishable Mode Cooling

ENERGIZED
DE- - ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
NOTE: HIGH SPEED EVAPORATOR FAN SHOWN. FOR LOW SPEED
CONTACT TE IS DE-ENERGIZED AND CONTACT TV IS ENERGIZED
5.3)
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER
NOTE
NOTE
5–10