51
Defrost and Temperature Control
Freezer and food compartment defrost and
temperature control is through the defrost and
temperature control daughter board.
Description of Operation
The defrost and temperature control controls
the operation of the cooling system fans,
freezer fan, fresh food compartment fan, and
automatic defrost cycle.
Freezer Fan
Freezer fan operation is controlled through
temperature input provided by the thermistor
attached to the freezer fin assembly and a
thermistor sensing freezer air temperature.
The fan turns on when freezer fin temperature
is below 10°F (-12°C) and cooling demand
is present or if thermistor resistance range is
less than 1.35 kΩ or greater than 250 kΩ and
cooling demand is present.
The fan turns off when freezer fin temperature
is above 20°F (-7°C), freezer air temperature
is below -5°F (-21°C), no cooling demand is
present or when the controls are in defrost.
Fresh Food Compartment Fan
Fresh food compartment fan operation is
controlled through a thermistor located on the
fresh food compartment fin assembly.
The fan turns on when fresh food fin temperature
is below 40°F (4°C) with cooling demand present
or if thermistor resistance is less than 1.6 kΩ or
more than 295 kΩ out of range.
The fan turns off when fresh food fin temperature
is above 50°F (10°C), no demand for cooling is
present or when the controls are in defrost.
Defrost Interval Timer
This timer counts cooling run time when freezer
temperature is below 30°F (-1°C). This value is stored
in non-volatile memory. The timer will count if freezer
fin temperature is open (greater than 250 kΩ). It will not
count if the thermistor is shorted (less than 1.35 kΩ).
Defrost Interval timer clears when freezer fin
temperature is above 30°F (-1°C) or if the freezer
fin thermistor is shorted (less than 1.35 kΩ).
When defrost interval timer reaches 780
minutes (13 hours) control initiates defrost.
When in defrost, cooling demand is inhibited,
the freezer and fresh food compartment fans
are turned off, the freezer heater and the fresh
food compartment heater are energized.
If the freezer fin climbs above 80 °F (26.6 °C)
during defrost, fault code A1 displays.
If the fresh food compartment fin climbs above 80°F
(26.6°C) during defrost, fault code A2 displays.
The A1 and A2 fault codes do not display if the
thermistor serving the assigned fin assembly is
open or shorted.
Freezer Heater
The freezer heater is de-energized when freezer
fin temperature climbs above 36°F (2°C) or of the
thermistor is out of range (<1.35kΩ or >250kΩ).
Drip Tray Heater
The drip tray heater is energized for 15 minutes after
the freezer heater is turned off. If manual defrost is
initiated, the drip tray heater will turn off.
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