Hoshizaki KM-320MAH - Manual (Page 17)

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) 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 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.
Dip Switch Setting Time
(seconds)
No. 1 No. 2
OFF OFF 60
ON OFF 90
OFF ON 120
ON ON 180