Hoshizaki KM-250BWF - Manual (Page 16)

16
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 (k
Ω)
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. 10. 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 k
Ω. Replace the thermistor if it exceeds the normal
reading.
2) 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 a longer setting by
adjusting the dip switch (No. 1 & 2) on the controller board.
SETTING TIME
Dip Switch Dip Switch
No. 1 No. 2
OFF OFF 60 seconds
ON OFF 90 seconds
OFF ON 120 seconds
ON ON 180 seconds