15
a) 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.
Check a thermistor for resistance by using the following procedures.
(1) Disconnect the connector K3 on the board.
(2) Remove the thermistor. See “V. H. Removal and Replacement of 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 k
Ω
. Replace the thermistor if it exceeds the normal
reading.
b) Defrost Timer
No adjustment is required under normal use, as the defrost timer is adjusted to the
suitable position. However, if necessary because all the ice formed on the evaporator
does not fall into the bin in the harvest cycle, adjust the defrost timer to a longer setting
by adjusting the dip switch (No. 1 & 2) on the controller board.
-18
14.401
-12
10.613
0
6.000
10
3.871
21
2.474
32
1.633
Temperature (°C) Resistance (k
Ω
)
No. 1
No. 2
OFF
OFF
60
ON
OFF
90
OFF
ON
120
ON
ON
180
Dip Switch Setting
Time
(seconds)
