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Freezer Section Defrost System
Defrost Thermostat
The defrost thermostat consists of a single pole
switch, a bimetal disc, and a transfer pin within a
metal and plastic case that is sealed with epoxy.
Lead wires, welded to the internal terminals, extend
through the case.
The purpose of the defrost thermostat, located on
the evaporator, is to de-energize the heater during
the defrost cycle. The defrost thermostat closes
at 23°F and opens at 64°F. After all frost has been
completely removed from the evaporator, the
temperature of the evaporator begins to rise rapidly.
When the limit temperature of the thermostat is
sensed, the bimetal disc warps and pushes the
transfer pin against a switch blade which opens the
switch contacts. Conversely, when the temperature
of the evaporator has cooled sufficiently, the
bimetal disc warps in the opposite direction. Then
the spring-loaded switch blade pushes the transfer
pin out of the way and closes the contacts.
Defrost Thermostat Removal
1.
Disconnect power to the refrigerator.
2. Remove freezer shelving.
3.
Remove the ice maker if one is installed (see
Ice
Maker Removal
section in this Guide).
4.
Remove the air tower (see
Air Tower Removal
section in this Guide).
5.
Remove the evaporator cover (see
Evaporator
Cover Removal
section in this Guide).
6.
Cut the wires at the defrost thermostat (since
the defrost thermostat is being discarded, cut
about 1 in. from the top of the thermostat).
7. Remove the defrost thermostat from the
evaporator.
The defrost thermostat has a metal clip that fastens
it to the evaporator suction line.
The image below represents a electro-mechanical
defrost control which has one defrost thermostat.
EDC control defrost systems have two defrost
thermostats that are ran in series with each other.
It is recommended to replace both defrost
thermostats if an open defrost thermostat is
discovered.
IMPORTANT
: When replacing defrost thermostats,
use only approved splicing techniques.
