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The safety thermostat (TCO) is a thermodisc (bimetal
switch) designed to ensure the defrost cycle doesn't
go into a run-away state. The TCO is in line with
the defrost heater and will open when it reaches a
temperature of 140 degrees F and close when the
evaporator temperature lowers to 110 degrees F.
Replacing Safety Thermostat
To replace a faulty thermostat the existing
thermostat will need to be cut from the harness and
the new thermostat will be spliced in its place.
NOTE: It is important to follow proper procedure
for splicing wires. New connections should use bell
FRQQHFWRUV¿OOHGZLWKDVLOLFRQHJUHDVHVXFKDV
WR97X163 or equivalent).
Defrost Heater
Safety Thermostat
The defrost heater is a ceramic heater which has a
resistance of 38 ohms and will receive 120 VAC from
the main board during defrost.
Diagnosing
• J9
(red) - J7 pin 9 (orange)
Note: Since the safety thermostat is also in line with
the defrost heater, when the heater circuit is open
from the main board it will be necessary to check
at the heater terminals to determine if the heater or
safety TCO is open.
Silicone Grease
