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1) Defrost Control
A thermistor (Semiconductor) is used for a defrost control sensor. The resistance
varies depending on the Suction Line temperatures. The Thermistor detects the
temperature of the Evaporator outlet to start the Defrost 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) Resistance (kΩ)
0 14.401
10 10.613
32 6.000
50 3.871
70 2.474
90 1.633
Check a thermistor for resistance by using the following procedures.
(i) Disconnect the connector K3 on the board.
(ii) Remove the Thermistor. See “V. 11. REMOVAL AND REPLACEMENT OF
THERMISTOR.”
(iii) Immerse the Thermistor sensor portion in a glass containing ice and water for 2 or 3
minutes.
(iv) 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.
Switch Nos. 9 and 10:
Used for adjustment of Freeze Timer.
The Freeze Timer determines maximum
freeze cycle time. Upon termination of
Freeze Timer, machine initiates the
harvest cycle. After 2 consecutive timer
terminations, machine will shut down,
possibly indicating a problem.