19
THERMISTOR TEST
Thermistors vary their resistance value according to the temperature they detect. For example, at
room temperature they have low resistance. When the temperature decreases, the resistance value
increases. The following table shows the approximate readings based on a temperature scale. In
fact, what is actually important about thermistors is that they must not show a reading of infinite
value (open) or zero resistance (closed), and when they turn hot or cold their resistance value
must vary.
Thermistors located in the freezer and in the fresh food compartment must have the same
characteristics and values; the difference stems from the type of connector and the temperature
they use to send a signal to the board.
TEMPERATURE RESISTANCE
TEMPERATURE RESISTANCE
40 °C (104ºF)
3,000
Ω
5 ºC (41ºF)
10,700
Ω
35 °C (95ºF)
3, 500
Ω
0 ºC (32ºF)
12,800
Ω
30 °C (86ºF)
4,100
Ω
-5
ºC
(23ºF) 16,000
Ω
25 °C (77ºF)
5,000
Ω
-10
ºC
(14ºF) 24,000
Ω
20 °C (68ºF)
6,000
Ω
-15
ºC
(5ºF) 34,000
Ω
15 °C (59ºF)
7,800
Ω
-20
ºC
(-4ºF) 45,000
Ω
10 ° C (50ºF)
9,300
Ω
NOTE:
THE VALUES BETWEEN EACH READING CAN VARY, BECAUSE THE
THERMOMETER SENSES TEMPERATURE FASTER THAN THE THERMISTOR (SINCE
THE THERMISTOR IS ENCAPSULATED). IF THE THERMISTOR IS KEPT AT A
CONSTANT TEMPERATURE, THE RESISTANCE VALUE WILL BE HIGHER, BECAUSE
BOTH THE THERMOMETER AND THE THERMISTOR TEMPERATURE WILL BE
STABLE.
COMPRESSOR OPERATING CYCLE
When the electronic board sends a signal to enable the operating cycle of the compressor, both
the potentiometer and the temperature sensor start operating to precisely regulate compressor
operation and keep food at the desired temperature. When the potentiometer's knob is turned, this
indicates to the sensor the temperature range under which the fresh food compartment must be
kept and, at the same time, the sensor, based on this range, sends a signal to indicate the
compressor's periods of operation and idleness.
DEFROST CYCLE
When the refrigerator is connected for the first time or after a long period of not using it, the
electronic board will send a signal to enable the defrost cycle after eight hours of accumulated
compressor operating time, depending on the time the resistance keeps connected during the
defrost cycle (20, 30, 40 minutes).
