GE Profile PSB42LGRBV, Technical Service Manual

Page: 39 / 72

– 39 –
Freezer Evaporator Thermistor
The evaporator thermistor is mounted in a copper
sleeve on the top, right corner of the evaporator.
Check for thermistor resistance (see
Thermistor
Chart
) by disconnecting the harness from CN06
and testing between the pin #3 (gray wire) and
pin #6 (red wire) on the harness.
Fresh Food Evaporator Thermistor
The fresh food evaporator thermistor is mounted
in a sleeve on the left side of the evaporator.
Check for thermistor resistance (see
Thermistor
Chart
) by disconnecting the harness at CN05 and
testing between pin #2 (gray wire) and pin #4
(pink wire) on the harness.
Thermistors
The main control board uses input from 5
thermistors:
• Ambient
• Freezer
• Fresh Food
• Freezer Evaporator
• Fresh Food Evaporator
The thermistors have a negative coeffi cient.
As the temperature increases, the thermistor’s
resistance decreases.
°F
Resistance In
Ohms (K
Ω
)
°C
-9 37K -23
-6 34K -21
0 29K -18
6 25K -14
32 13K 0
37 12K 3
50 8.8K 10
77 5K 25
86 4.2K 30
95 3.5K 35
Thermistor Chart
Thermistor Emergency Operation
If the freezer thermistor opens (or shorts), the unit
defaults to the freezer evaporator thermistor. The
compressor and freezer fan cycle off when the
freezer evaporator temperature is -22°F (-30°C)
or colder. The compressor and freezer fan cycle
on when the freezer evaporator temperature is
-2°F (-19°C) or warmer.
If the fresh food thermistor opens (or shorts),
the fresh food cooling operation defaults to the
freezer thermistor. Refrigerant will fl ow through
the fresh food evaporator any time the freezer
evaporator is cooling. The fresh food fan will cycle
off once the fresh food evaporator thermistor
reaches 5°F (-15°C) or colder.
Note: Thermistors can also be checked for an
open or shorted condition by using the diagnostic
mode (see
Service Diagnostics
).
Ambient Thermistor
The ambient thermistor measures room
temperature and is clipped to the back of the
dispenser cover. Check for thermistor resistance
(see
Thermistor Chart
) by disconnecting the
harness at CN03 and testing between pin #4
(gray wire) and pin #6 (red wire) on the harness.
Freezer Air Thermistor
The freezer air thermistor is clipped to the inside
of the evaporator cover.
Check for thermistor resistance (see
Thermistor
Chart
) by disconnecting the harness at CN06 and
testing between pin #3 (gray wire) and pin #5
(brown wire) on the harness.
Fresh Food Air Thermistor
The fresh food air thermistor is clipped to
the inside of the ceiling cover. Check for
thermistor resistance (see
Thermistor Chart
) by
disconnecting the harness at CN05 and testing
between pin #2 (gray wire) and pin #3 (yellow
wire) on the harness.
Testing
The most accurate
method of testing a
thermistor is to place it
in a glass of ice water
for several minutes. The
thermistor should read
approximately 13K
Ω
in the glass of 33°F ice
water.