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T-305
52
When a defrost has terminated, the defrost interval
timer will begin counting when the reading at the Defrost
Temperature Sensor is at or below 10
°
C(50
°
F). Once
the timer has counted the required time, the unit will
enter defrost if the Defrost Temperature Sensor is at or
below 25.6
°
C(78
°
F). Defrost will terminate when the
Defrost Sensor Temperature reading rises above the
CnF41 setting.
When the unit enters defrost, the controller opens
contacts TC, TN and TE (or TV) to de-energize the
compressor, condenser fan and evaporator fans. (See
Figure 21.) The COOL light is also de--energized.
The controller then closes TH to supply power to the
heaters. The defrost light is illuminated.
When the defrost temperature sensor reading rises to
the applicable Defrost Termination Thermostat
“opening” point the de--icing operation is terminated.
If defrost does not terminate correctly and temperature
reaches the set point of the heat termination thermostat
(HTT) the thermostat will open to de--energize the
heaters. If termination does not occur within 2.0 hours,
the controller will terminate defrost. An alarm will be
given of a possible DTS failure.
If probe check (controller function code CnF31) is
configured to special, the unit will proceed to the next
operation (snap freeze or terminate defrost). If the code
is configured to standard, the unit will perform a probe
check. The purpose of the probe check is to detect
malfunctions or drift in the sensed temperature that is
too small to be detected by the normal sensor out of
range tests. The system will run for eight minutes in this
condition. At the end of the eight minutes, probe alarms
will be set or cleared based on the conditions seen.
When the return air falls to 7
_
C (45
_
F), the controller
checks to ensure the defrost temperature sensor (DTS)
reading has dropped to 10
_
C or below. If it has not, a
DTS failure alarm is given and the defrost mode is
operated by the return temperature sensor (RTS).
If controller function code CnF33 is configured to snap
freeze, the controller will sequence to this operation.
The snap freeze consists of running the compressor
without the evaporator fans in operation for a period of
four minutes with the suction modulation valve at
maximum allowed opening. When the snap freeze is
completed, defrost is formally terminated.
4.11 EMERGENCY OPERATION
Operation by the refrigeration controller may be
overridden by use of the EMERGENCY BYPASS or by
use of the EMERGENCY DEFROST switch. The
EMERGENCY BYPASS switch functions to bypass the
controller in the event of controller failure, The
EMERGENCY DEFROST switch functions to bypass
the controller and place the unit in the defrost mode.
4.11.1 Emergency Bypass Operation
To place the unit in the emergency bypass mode of
operation, cut the wire tie installed at the switch
mounting (see Figure 6) and place the switch in the
EMERGENCY BYPASS COOLING position.
The switch is a normally open four pole switch which is
placed in the EMERGENCY BYPASS COOLING
position to:
a. Provide power to the compressor contactor with the
high pressure switch and compressor motor internal
protector in line.
b. Provide power to the condenser fan motor contactor
with the water pressure switch and condenser motor
internal protector in line.
c. Provide power to the evaporator fan motor high
speed contactors with the evaporator fan motor inter-
nal protectors in line.
d. Provide power to the bypass module (item14,
Figure 3, page 7). The bypass module supplies pow-
er to the stepper motor drive to bring the valve to the
full open position.
CAUTION
The unit will remain in the full cooling mode
as long as the emergency bypass switch is
in the BYPASS position. If the cargo may be
damaged by low temperatures, the operator
must monitor container temperature and
manually cycle operation as required to
maintain temperature within required lim-
its.
To return the unit to normal operation, place the switch in
the NORMAL OPERATION position. When emergency
oparation is no longer required, re--install the wire tie at
the switch mounting.
4.11.2 Emergency Defrost Operation.
To place the unit in the emergency defrost mode of
operation, cut the wire tie installed at the switch
mounting (see Figure 6) and place the switch in the
EMERGENCY DEFROST position.
NOTE
1. If the unit is in the emergency bypass
cooling mode, the emergency defrost
switch will override this mode and place the
unit in defrost.
2. The IN--RANGE LIGHT is de--energized
when in the emergency defrost mode.
The switch is a normally open four pole switch which is
placed in the EMERGENCY DEFROST position to:
a. De--energize the compressor, condenser fan and
evaporator fan contactors.
b. Illuminate the EMERGENCY DEFROST LIGHT.
c. Energize the heater contactor.
d. Illuminate the DEFROST LIGHT.
CAUTION
The unit will remain in the DEFROST mode
as long as the emergency defrost switch is
in the DEFROST position. To prevent cargo
damage, the operator must monitor con-
tainer temperature and manually cycle op-
eration as required to maintain temperature
within required limits.
To return the unit to normal operation, place the switch in
the NORMAL OPERATION position. When emergency
defrost is no longer required, re--install the wire tie at the
switch mountiing.
Содержание 69NT40-489-100 Series
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