Perishable Mode Heating − Sequence Of Operation; Frozen Mode - Temperature Control; Frozen Steady State; Figure 4.7 Perishable Mode Heating - Carrier 69NT40-541-505 Operation And Service Manual

b. When supply air temperature decreases to a
predetermined tolerance above set point
(Cd30), the green IN RANGE light is illuminated.
c. As the air temperature continues to fall, modu-
lating cooling starts as the supply air tempera-
ture approaches set point.
d. The controller continuously monitors supply air
temperature. Once the supply air temperature
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 to determine tem-
perature drift from set point over time. If the cal-
culation 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.
e. The evaporator fan motors continue to run to cir-
culate air throughout the container. The green
IN−RANGE light remains illuminated as long as
the supply air is within tolerance of set point.
f. When the supply air temperature increases to
0.2°C (0.36°F) above set point and the three
minute off time has elapsed, relays TC and TN
are energized to restart the compressor and
condenser fan motor. The white COOL light is
also illuminated.
4.3.10 Perishable Mode Heating − Sequence of
Operation
The unit will heat only when in the Perish-
able Mode, relay TH is electronically locked
out when in the Frozen Mode.
a. If the supply air temperature decreases 0.5°C
(0.9°F) below set point, the system enters the
heating mode (see
closes contacts TH (see
power flow through the heat termination thermo-
stat (HTT) to energize the heaters (HR). The
orange HEAT light is also illuminated. The evap-
orator fans continue to run to circulate air
throughout the container.
b. When the supply temperature rises to 0.2°C
(0.36°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. The safety heater termination thermostat (HTT)
is attached to an evaporator coil circuit and will
open the heating circuit if overheating occurs.
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NOTE
Figure 4.5). The controller
Figure
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Figure 4.7 Perishable Mode Heating

FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
4.3.11
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.
With CnF26 (Heat Lockout Temperature) is set to -
10°C, frozen mode is active with set points at or below -
10°C (+14°F). With CnF26 set to -5°C, frozen mode is
active at or below -5°C (+23°F).
When the system is in Frozen Mode, the highest prior-
ity is given to bringing the container down to set point.
When return air temperature is greater than 0.2°C
(0.36°F) above the frozen set point and the three min-
ute time delay has been met, the unit will always oper-
4.7) to allow
ate at full capacity with the suction modulation valve
open as allowed by current and pressure limiting.
4.3.12
Frozen range cargoes are not sensitive to minor tem-
perature changes. The method of temperature control
employed in frozen range takes advantage of this fact
to greatly improve the energy efficiency of the unit.
Temperature control in frozen range is accomplished
by cycling the compressor on and off as the load
demand requires.
The unit will operate in the conventional frozen mode
when the controller set point is at or below the frozen
range and Economy Mode (Cd34) is set to "OFF."
4–7
ENERGIZED
DE-ENERGIZED
CONTROL TRANSFORMER
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
CONTROLLER

Frozen Mode - Temperature Control

Frozen Steady State

SIGNAL TO
T-368