Adaptive Defrost Theory Of Operation - Viking VCSB481 Service Notebook

Electronic Function Description
IMPORTANT: When the showroom switch is OFF, the isolator sees line voltage which keeps the electronic
controller from signaling the evaporator fan motor or compressor relay coils and keeps the fresh food and
condensate evaporator fans off.

Adaptive Defrost Theory of Operation

After designated compressor run time, refrigeration
cycle is interrupted and electronic control sends a low
voltage signal to defrost relay coil (def D1).
Powering the relay coil closes contact (D1)
completing high voltage circuit to defrost heater
through closed defrost terminator (closes at 15°F).
Isolator, which is part of high voltage PC board,
recognizes presence of line voltage to defrost heater
and sends low voltage signal to electronic control..
Electronic control keeps count of number of minutes
defrost terminator remains closed (opens at 48°F).
Length of time defrost terminator is closed
determines if the next defrost cycle advances by 4
hours of compressor run, stays at the same interval,
or delays be 4 hours of compressor run.
If defrost terminator does not open before 29
minutes, defrost cycle is automatically terminated by
electronic control and refrigeration cycles will
resume after 6 minutes dwell time.
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