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Fresh Food Extended Defrost #1
Occasionally there may be excessive frost on
the evaporator coil. This can be attributed to
numerous door openings, extremely high humid-
ity, poor door gasket seal, etc. If the normal
defrost fan time exceeds 60 minutes, the fan
switches to high speed. The control continues to
monitor the fresh food evaporator thermistor for
1°C. When 1°C is reached, the fan runs for an
additional 5 minutes at high speed. The fan can
run up to an additional 30 minutes at high
speed, trying to reach 1°C. After 90 total min-
utes of fan time (60 at low speed and 30 at
high speed), if the fresh food evaporator is still
below 35°F, the control will switch to extended
defrost #2.
Fresh Food Extended Defrost #2
If the fresh food fan has been operating for 90
minutes, the main control searches for a fresh
food thermistor temperature above 11°C. If the
fresh food thermistor is above 11°C, the main
control board assumes there is a problem
reading the fresh food evaporator thermistor,
ends the defrost cycle and returns to normal
cooling.
If the fresh food thermistor is less than 11°C,
the main control board assumes there is refrig-
erant leaking through the 3-way valve, keeping
the fresh food evaporator cold during the de-
frost process while the freezer evaporator is
cooling. The main control board shuts off the
compressor and runs the fresh food fan at high
speed until two conditions are met: the evapora-
tor thermistor reaches 1°C and the fresh food
thermistor is 1°C above the set point. As in the
other cycles, the fan continues to run for an
additional 5 minutes after the 35°F evaporator
temperature is reached.
Fresh Food Forced Defrost
If the main control board senses the fresh food
section has been cooling for 45 minutes, it
immediately stops the refrigerant flow through
the fresh food evaporator. The main control
board changes the position of the 3-way valve
if cooling is still required in the freezer, or turns
the compressor off if the freezer is satisfied. The
fresh food fan operates on high speed until the
evaporator reaches 1°C, plus an additional 5
minutes after the evaporator reaches 1°C.
To prevent the refrigerator from going into
forced defrost when first installed or after a
power failure, the control will disregard the 45
minute time limit if the freezer temperature is
above (-6)°C.
Note: If the fresh food evaporator thermistor is
either open or shorted and the 1°C cutoff cannot
be determined, the main control board defaults
to a fixed defrost cycle of 1 hour at high-speed
fan.
Freezer Defrost Cycle
The freezer evaporator utilizes a defrost heater
to remove frost from the coil. The control board
determines the length of time the heater is
energized. It does this by monitoring the freezer
evaporator thermistor. Once the temperature of
the thermistor reaches 23°C, the control cycles
the defrost heater off. A bi-metal safety thermo-
stat provides a backup in the event the evapora-
tor thermistor fails. The safety thermostat pre-
vents the temperature from exceeding 60°C.
Note: During the freezer defrost cycle, the
compressor does not operate, even if the fresh
food section is above the set point.
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