Carrier 69NT40-541-300, Операция и обслуживание, Страница: 39 / 152

T-318 3 − 7
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, modulating
cooling starts as the supply air temperature
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 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
condenser fan motor.
e. 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 is
within tolerance of set point.
f. 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 energized to re-
start the compressor and condenser fan motor. The
white COOL light is also illuminated.
3.3.10 Perishable Mode Heating − Sequence of
Operation
NOTE
The unit will heat only when in the Perishable
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 Figure 3-5). The controller closes contacts 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 illuminated. The
evaporator fans continue to run to circulate air
throughout the container.
b. When the supply temperature rises to 0.2 ° C (0.4 ° 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 at-
tached to an evaporator coil circuit and will open the
heating circuit if overheating occurs.
CONTROL TRANSFORMER
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
SIGNAL TO
CONTROLLER
ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
Figure 3-7 Perishable Mode Heating
3.3.11 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.
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 priority
is given to bringing the container down to set point.
When return air temperature is greater than 0.2 C
(0.4 F) above the frozen set point and the three minute
time delay has been met, the unit will always operate at
full capacity with the suction modulation valve open as
allowed by current and pressure limiting.
3.3.12 Frozen Steady State
Frozen range cargoes are not sensitive to minor
temperature 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.”