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Adaptive Defrost
Adaptive Defrost can be described as a defrost
system that adapts to a refrigerator’s surrounding
environment and household usage.
Unlike conventional defrost systems that use
electromechanical timers with a fixed defrost cycle
time, Adaptive Defrost utilizes an intelligent,
electronic control to determine when the defrost
cycle is necessary. In order to accomplish the
correct defrost cycle time, the main control board
monitors the following refrigerator operations:
•Length of time the refrigerator doors were open
since the last defrost cycle
•Length of time the compressor has run since
the last defrost cycle
•Amount of time the defrost heaters were on in
the last defrost cycle
Adaptive Defrost is divided into 4 separate cycles.
Those operations are:
•Cooling Operation
•Pre-Chill Operation
•Defrost Heater Operation
•Dwell Period
(See Pub. #31-9062 for more information on
Adaptive Defrost.)
Adaptive Defrost (Cooling Operation)
During the cooling operation, the main control
board monitors door opening (fresh food door and
freezer drawer) and compressor run times. The
board counts the time the doors are open. It
reduces the length of time between defrosts by
300 seconds (multiplication factor) for each
second that each door is open (if both doors are
open, it reduces it by twice the amount). The
multiplication factor reduces compressor run time.
If the doors are not opened, the compressor will
run up to 60 hours between defrosts. If the doors
are opened frequently and/or for long periods of
time, the compressor run time between defrosts
will be reduced to as little as 8 hours.
Adaptive Defrost (Pre-Chill Operation)
When the main control board determines that
defrost is necessary, it will force the refrigerator
into a continuous cool mode (pre-chill). During pre-
chill, the freezer temperature may be driven below
the set point. However, the fresh food temperature
will be regulated by the evaporator fan running at
low speed. Pre-chill will last for 30 minutes. These
models do have an 8-hour defrost holdoff.
Adaptive Defrost (Defrost Heater Operation)
After 30 minutes of pre-chill operation, the main
control board turns off the compressor, condenser
fan, and evaporator fan.
During defrost operation, the main control board
monitors the evaporator temperature using
evaporator thermistor inputs. Typically, the
evaporator thermistor will sense a temperature of
38 °F within 16 minutes. When the thermistor
senses 38 °F, the main control board will terminate
defrost heater operation. Maximum defrost cycle
(heater on) time is 35 minutes (main control board
time out).
The defrost system is protected by a defrost
overtemperature thermodisc (bimetal switch). The
thermostat opens when the evaporator
temperature raises to 60 °F and closes when the
evaporator temperature lowers to 45 °F.
Adaptive Defrost (Dwell Period)
After defrost heater operation has been terminated
by the main control board, a 20-minute dwell
period occurs. During this period, the
compressor, condenser fan, and evaporator fan
remain off. The remaining frost melting from the
evaporator will continue to drip and drain so that,
prior to the cooling operation, the evaporator will be
totally clear of any moisture. The pan heater is on
for the entire 20 minute dwell period.
Defrost System