Carrier Transicold 69NT40-561-001, Operation And Service Manual, Page: 44 / 182

T-340 4–8
Figure 4.6 Perishable Mode Cooling
b. When supply air temperature decreases to a predetermined tolerance above set point (Cd30), the green IN
RANGE light is illuminated.
c. As air temperature continues to fall, unloaded cooling starts (DUV pulses opens) as the supply air tempera -
ture approaches set point (see Figure 4.5 ).
d. When unloaded cooling starts, EEV control will transition from a full cool superheat set point to a lower mod -
ulated cool superheat set point. Once unloading starts, the EEV controls evaporator superheat based on the
system duty cycle where instantaneous superheat will vary.
e. When the supply air temperature has fallen to within 1.9°C (3.4°F) of set point temperature and the average
capacity of the system has fallen below 70%, the unit will open contacts TS to close the ESV and take the
unit out of economized operation.
f. The controller continuously monitors supply air temperature. Once the supply air temperature falls below set
point, the controller periodically records supply air temperature, set point and time. A calculation is then per -
formed to determine temperature drift from set point over time. If the calculation determines that cooling is
no longer required, contacts TC and TN are opened to de-energize the compressor motor and the con -
denser fan motor. In addition the controller will close the EEV.
g. The evaporator fan motors continue to run to circulate air throughout the container. The green IN RANGE
light remains illuminated as long as the supply air temperature is within tolerance of the set point.
h. If the supply air temperature increases to 1.0°C (1.8°F) above set point and three minutes have elapsed,
contacts TC and TN close to restart the compressor and condenser fan motors in standard mode (non-
economized) operation. The white COOL light is also illuminated.
i. If the average system capacity has risen to 100% during unloaded cooling and three minutes off time has
elapsed, relay TS will energize to open the ESV, placing the unit in economized mode.
j. If the supply air increases more than 2.5°C (4.5°F) above set point temperature, the microprocessor will
transition the evaporator superheat control from modulation back to full cool control.
4.3.12 Perishable Mode Heating - Sequence of Operation
a. If the supply air temperature decreases 0.5°C (0.9°F) below set point, the system enters the heating mode
(see
Figure 4.5
). The controller closes contacts TH (see
Figure 4.7
) to allow power flow through the heat
termination thermostat (HTT) to energize the heaters (HR). The orange HEAT light is also illuminated. The
evaporator fans continue to run to circulate air throughout the container.
b. When the supply air temperature rises to 0.2°C (0.4°F) below set point, contact TH opens to de-energize the
heaters. The orange HEAT light is also de-energized. The evaporator fans continue to run to circulate air
throughout the container.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
ST
F
HPS
CH
IP-CM
TC
CF
TE
IP-EM1
EF
IP-EM2
HTT
TH
HR
ESV
TS
TV
EF
ES