Viking VCSB360 Service Notebook page 11

Defrost System
As air circulates through the refrigerator/freezer, moisture from food and outside air that enters whenever
the doors are opened condenses and freezes onto the evaporator coils and fins to form a layer of frost.
Periodically the frost must be cleared from the coils so that the air flow is not blocked. An automatic
defrost function accomplishes this task with the use of a defrost timer, defrost heater and bimetal.
The defrost system is designed to initiate the defrost function following 10 hours of accumulated
compressor run time. The defrost timer motor runs during a cooling cycle when the compressor runs and
stops running when the compressor cycles off. The timer motor also runs during the defrost cycle when
the refrigeration system is shut down.
Once initiated, the defrost cycle lasts 21 minutes. The defrost heater is energized and melts off any frost
accumulation. When the evaporator area reaches approximately 50* F, the bimetal opens and turns off
the defrost heater. This usually occurs 10 to 15 minutes after the defrost cycle begins. The defrost timer
motor continues the defrost cycle for the full 21 minutes duration and then the cooling cycles resume.
During the defrost cycle the following occurs:
The thermostat is bypassed and has no controlling function.
The compressor run signal current, from the thermostat to the electronic control board,
is interrupted. The electronic control board will not sense or regulate the temperature.
Voltage is interrupted from the thermostat to the electronic control board.
a)
b)
The Mullion and Condensate Pan Heat Loop
The mullion and condensate pan heat loop (Fig.8 A) enters the separator wall through a grommet in the
back of the cabinet (Fig.8 B) where it travels inside the separator wall to the front. It then bends 90* (1)
and travels along the entire length of the separator (2) to the bottom of the cabinet. Finally, the loop
bends 90* (3) and travels along the bottom of the separator and exits through a grommet at the back of the
cabinet.
The loop then makes a 180* trap and travels down underneath the cabinet and forms a coil over the
condensate pan. The loop then travels up the back of the cabinet to the condenser.
The Freezer Side Panel Heater
The freezer side panel heater element (4) is affixed to an adhesive sheet on the left inside wall of the outer
cabinet and is foamed in place during manufacture. The element covers the bottom half of the wall and is
energized whenever the freezer thermostat initiates a cooling cycle and the compressor runs. The plug (5)
for the freezer side heater is located near the top left corner of the cabinet.
The evaporator fan motor does not run.
The motorized air door does not operate. The air door stays in its present position
(either open or closed) until the defrost cycle is over.
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