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2. In
low
temperature
condenser fan will be cycled by the
controller to maintain proper condensing
pressure.
a. With supply air temperature above set point and de-
creasing, the unit will be cooling with the condenser
fan motor (CF), compressor motor (CH), evaporator
fan motors (ES) energized and the COOL light illumi-
nated. (See Figure 20.)
b.When the air temperature decreases to a predeter-
mined tolerance above set point, the in-range light is
illuminated.
ENERGIZED
DE- -ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 13
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
Figure 20. Frozen Mode
c. Contacts TC and TN are opened to de-energize the
compressor and condenser fan motors when the re-
turn air temperature decreases to 0.2_C (0.4_F) be-
low set point. The cool light is also de-energized.
d. The evaporator fan motors continue to run to circulate
air throughout the container. The in-range light re-
mains illuminated as long as the return air is within tol-
erance of set point.
e. When the return 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 energizes to re-
start the compressor and condenser fan motors. The
cool light is also illuminated.
4.10.4 Sequence Of Operation - - Defrost Mode
NOTE
Unit will not initiate defrost if the EverFresh
Controlled Atmosphere (CA) system is in the
Vent or Pre-trip mode.
The defrost cycle may consist of up to three distinct
operations. The first is de-icing of the coil, the second is
a probe check cycle and the third is snap freeze.
Defrost may be requested by any one of the following
methods:
ambients
the
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER
1. The manual defrost switch (MDS) is closed by the
user.
2. The user sends a defrost request by communica-
tions.
3. The defrost interval timer (controller function code
Cd27) reaches the defrost interval set by the user.
4. The controller probe diagnostic logic determines that
a probe check is necessary based on the tempera-
ture values currently reported by the supply and re-
turn probes.
5. The controller Demand Defrost configuration vari-
able (CnF40) is set to "In" and the unit has been in
pull down operation for over 2.5 hours without reach-
ing set point.
ENERGIZED
DE- -ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 13
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
SIGNAL TO
CONTROLLER
Figure 21. Defrost Mode
Processing of a defrost request is controlled by the
Defrost
Termination
Termination Thermostat is not a physical component. It
is a software point that acts as a thermostat, allowing
defrost when it is considered "closed" and preventing or
terminating defrost when it is considered "open". The
actual temperatures used to make the "open" or
"closed" determinations are dependent on the type of
defrost request made and the operator setting of
configuration variable CnF41. Configuration variable
CnF41may be factory set at the default value of
25.6°C(78°F) or a lower value of 18°C(64°F).
When a request for defrost is made by the use of the
Manual Defrost Switch or Communications, the unit will
enter defrost when the reading at the Defrost
Temperature Sensor is at or below the CnF41 setting.
Defrost will terminate when the Defrost Sensor
Temperature reading rises above the CnF41 setting.
When a request for defrost is made by probe check, the
unit will enter defrost when the Defrost Temperature
Sensor reading is at or below 25.6°C(78°F). The unit will
terminate defrost when the Defrost Temperature
Sensor reading rises above 25.6°C(78°F)
When a request for defrost is made by demand defrost ,
the unit will enter defrost when the reading at the Defrost
Temperature Sensor is at or below 18°C (64.4°F).
Defrost will terminate when the Defrost Sensor
Temperature reading rises above the CnF41 setting.
51
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER
Thermostat.
The
Defrost
T-305
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