Hoshizaki KM-320MAH Service Manual page 17

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.
Temperature (°F) Temperature (°C)
Check a thermistor for resistance by using the following procedure:
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 kΩ.
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 when all the ice formed on the evaporator does
not fall into the bin in the harvest cycle, adjust the defrost timer to longer setting by
adjusting the dip switch (No. 1 & 2) on the controller board.
0 -18
10 -12
32 0
50 10
70 21
90 32
Dip Switch Setting
No. 1 No. 2
OFF OFF
ON OFF
OFF ON
ON ON
17
Resistance (kΩ)
14.401
10.613
6.000
3.871
2.474
1.633
Time
(seconds)
60
90
120
180