Service manual

T -318
4-- 9
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.
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 4-8). 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 two 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.
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.
4.1 1.1 Emergency Bypass Operation
To place the unit in the emergency bypass mode, cut the
wire tie installed at the switch mounting and place the
EMERGENCY BYPASS switch in the ON position. This
will in turn activate the Emergency Bypass System
(EBS) control module.
To operate the fans only, the MODE switch must be in
the FANS ONLY position and the EMERGENCY
BYPASS Switch must be in the ON posit ion.
The EBS module uses the system’s safety devices (high
pressure switch, motor internal protectors, and heat
termination thermostat) to protect the system while in
Emergency Bypass Mode.
CAUTION
The unit will remain in the full cooling mode
as long as the emergency bypass switch is
in the BYPASS position and the MODE
SWITCH is in the FULL COOL position. If
the cargo may be damaged by low tempera-
tures, the operator must monitor container
temperature and manually cycle operation
as required to maintain temperature within
required limits.
In the ON position the EBS will be enabled. With the
MODE SWITCH in the FULL COOL MODE. The
following will occur simultaneously:
1. The EBS switch will enable EBS input.
2. The phase detection circuit will detect the phase
rotation and close to provide power to the compres-
sor contactor.
3. The condenser fan contact will close to energize the
condenser contactor and provide power to the con-
denser fan motor.
4. The evaporator fan contact will close to energize the
high speed evaporator contactor and provide power
to the evaporator fan motor.
5. The EBS electronic module will open the SMV to
100%.
To return the unit to normal operation, place the EBS
switch in the NORMAL OPERATION position. When
emergency operation is no longer required, re-install the
wire tie at the switch mounting.
4.1 1.2 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 2-6) 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.