Hoshizaki KM-320MWH, KM-320MAH service manual Defrost Control

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
No. 1	No. 2	(seconds)
OFF	OFF	60
ON	OFF	90
OFF	ON	120
ON	ON	180

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