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5. Control Board Replacement
The dip switches should be adjusted to the factory default settings as outlined in this
manual. S4 dip switch #8 must remain off.
D. Harvest Control – Thermistor
A thermistor (semiconductor) is used for a harvest control sensor. The resistance varies
depending on the suction line temperatures. The thermistor detects the temperature of
the evaporator outlet to start the harvest timer. 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 -1 10.614
3 0 6.000
50 10 3.871
70 1 .474
90 3 1.633
Check a thermistor for resistance by using the following procedure:
1) Disconnect the connector K3 on the board.
) Remove the thermistor. See "V.C.6. Removal and Replacement of Thermistor."
3) Immerse the thermistor sensor portion in a glass containing ice and water for 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.