15
4. HARVEST CONTROL – THERMISTOR
A thermistor (semiconductor) is used as a harvest control sensor, anti-slush sensor, and
overfreeze sensor.
The resistance varies depending on the suction line temperatures. The thermistor detects
the temperature of the evaporator outlet to start the harvest timer, to momentarily stop the
pump motor during the freeze cycle, or to extend the harvest cycle time. No adjustment is
required. If necessary, check for resistance between thermistor leads, and visually check
the thermistor mounting, located on the suction line next to the evaporator outlet.
Temperature (°F)
Temperature (°C)
Resistance (kΩ)
0
-18
14.401
10
-12
10.613
32
0
6.000
50
10
3.871
70
21
2.474
90
32
1.633
Check a thermistor for resistance by using the following procedure:
1) Disconnect the thermistor (orange wires) at the 2-pin connector on the control box. See
Fig. below.
2) Remove the thermistor. See "V. 17. THERMISTOR."
3) Immerse the thermistor sensor portion in a glass containing ice and water for 2 or 3
minutes.
4) Check for a resistance between thermistor leads. Normal reading is within 3.5 to 7 kΩ.
Replace the thermistor if it exceeds the normal reading.
Thermistor Connector
(orange wires)
Bin Control Wires
(black)
Float Switch Connector
(red wires)
