T-372
4–8
4.3.12
Perishable Mode Heating - Sequence of Operation
a. If the supply air temperature decreases 0.5°C (0.9°F) below setpoint, the system enters the Heating Mode
(see
). The controller closes contacts TH (see
) 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 setpoint, 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.
c. The safety HTT is attached to an evaporator coil circuit and will open the heating circuit if overheating
occurs.
Figure 4.6 Perishable Mode Heating
NOTE
The electronic expansion valve (EEV) and digital unloader valve (DUV) are independently operated by
the microprocessor. For full diagrams and legend, see
4.3.13
Perishable Mode - Trim Heat
If the system capacity has been decreased to the lowest allowable capacity and conditions exist that warrant max
-
imum temperature stability, the controller will pulse the HR relay to energize the evaporator heaters in sequence
with the compressor digital signal.
4.3.14
Frozen Mode (Temperature Control)
In Frozen Mode, the controller maintains the return air temperature at setpoint, the yellow RETURN indicator light is
illuminated, and the default reading on the display window is the return temperature sensor (RTS) reading.
When the return air temperature enters the in-range temperature tolerance (Cd30), the green IN-RANGE light will
energize.
When CnF26 (Heat Lockout Temperature) is set to -10°C, Frozen Mode is active with setpoints below -10°C
(+14°F). When CnF26 is set to -5°C, Frozen Mode is active with setpoints below -5°C (+23°F).
When the system is in Frozen Mode, the highest priority is given to bringing the container down to setpoint. The
system will remain in economized operation.
4.3.15
Frozen Steady State Mode
Frozen cargos are not sensitive to minor temperature changes, and the frozen temperature control system takes
advantage of this to greatly improve the energy efficiency of the unit. Frozen range temperature control is accom
-
plished by cycling the compressor on and off as the load demand requires. Once the frozen setpoint is reached, the
unit will transition to Frozen Steady State Mode (economized operation).
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
