GE PSH23SGNAFBS Series, Technical Service Manual

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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 5 separate cycles.
Those operations are:
• Cooling Operation
• Pre-Chill Operation
• Defrost Heater Operation
• Dwell Period
• Post Dwell
(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 and
freezer doors) and compressor run times. The
length of time between consecutive defrosts is
reduced by each door opening. 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 damper. Pre-chill will
continue until one of the following 3 conditions
have been met.
• freezer temperature of -9 °F
• evaporator temperature of -25 °F
• 110 minutes of continuous run time with no
door openings
The average pre-chill is complete within 30 to
40 minutes. This model does not have a defrost
holdoff.
Adaptive Defrost (Defrost Heater Operation)
After pre-chill has concluded, 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
70 °F within 20 to 30 minutes. When the
thermistor senses 70 °F, the main control board
will terminate defrost heater operation. Maximum
defrost cycle (heater on) time is 40 minutes (main
control board time out).
The defrost system is protected by a defrost
termination thermostat (bimetal switch). The
thermostat opens when the evaporator
temperature raises to 140 °F and closes when the
evaporator temperature lowers to 110 °F.
Adaptive Defrost