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Defrost Heater
The defrost heater is a single-tube, radiant
heater. It is held in place by 2 tabs on the
evaporator (1 on each side) and by 2 ceramic
and wire supports.
The ceramic and wire supports prevent the
heater from sagging and touching the metal
drain pan if the glass is broken.
Defrost Heater Supports
Defrost Drain Probe
Heater Supports
Evaporator Thermistor
Defrost Overtemperature Thermostat
Evaporator Thermistor
The evaporator thermistor is mounted on the
upper right side of the evaporator. The defrost
cycle will terminate when the main control board
detects 65°F from the evaporator thermistor.
The main control board must sense 65°F in less
than 45 minutes, or the defrost cycle will time
out. Normal defrost time is 25 minutes or less,
not including the 5-minute dwell or post dwell
periods.
Defrost Overtemperature Thermostat
The defrost overtemperature thermostat
(bimetal switch) is mounted on the evaporator
and provides overtemperature protection during
defrost. This thermostat will open at 140°F and
will close at 110°F.
Note:
The main control board will not know if
the heater does not come on due to a broken
heater, open defrost overtemperature
thermostat, or an open wiring harness. The
defrost heater is controlled by maximum time on
the main control board or temperature at the
evaporator thermistor.
