3−7
T-364
3.3.10 Perishable Mode Heating - Sequence of
Operation
a. If the supply air temperature decreases 0.5C
(0.9F) below set point, the system enters the heating
mode. (See Figure 3−5). The controller closes con-
tacts TH (see Figure 3−7) to allow power flow through
the heat termination thermostat (HTT) to energize the
heaters (HR). The orange HEAT light is also illumin-
ated. The evaporator fans continue to run to circulate
air throughout the container.
b. When the supply air temperature rises to 0.2C
(0.4F) below set point, contact TH opens to de-ener-
gize 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 heater termination thermostat (HTT) is at-
tached to an evaporator coil circuit and will open the
heating circuit if overheating occurs.
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
Figure 3−7 Perishable Mode Heating
NOTE
The EEV and DUV are independently operated
by the microprocessor. For full diagrams and
legend, see Section 7.
3.3.11 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.
3.3.12 Frozen Mode - Temperature Control
In Frozen Mode, the controller maintains the return air
temperature at set point, 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 set point is below -10C (14F), frozen mode is
active.
When the system is in Frozen Mode, the highest priority
is given to bringing the container down to set point, the
system will remain in economized operation.
3.3.13 Frozen Steady State
Frozen cargos are not sensitive to minor temperature
changes, and the frozen temperature control system
takes advantage of this to greatly improve the energy ef-
ficiency of the unit. Frozen range temperature control is
accomplished by cycling the compressor on and off as
the load demand requires.
Once the frozen set point is reached, the unit will transi-
tion to frozen steady state (economized operation).
3.3.14 Frozen Idle Mode
When temperature drops to set point minus 0.2C
(0.4F) and the compressor has run for at least five min-
utes, the unit will transition to the frozen idle mode. The
compressor is turned off and the evaporator fans contin-
ue to run to circulate air throughout the container. If tem-
perature rises above set point +0.2C, (+0.4F) the unit
will transition back to the frozen steady state mode.
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