Hoshizaki HR24A service manual C. Thermistor Check

b)Defrost Termination: Comp icon is on. EvapFM icon flashing. 30-min. DT terminates. 6-hr. DT starts. Comp icon turns on and Comp energizes. 2-min. EvapFM timer starts. EvapFM icon starts flashing and EvapFM de-energizes. When 2-min. EvapFM timer terminates, EvapFM icon turns steady and EvapFM energizes. Normal operation resumes. Diagnosis: Has appliance been in defrost for 30 min.? If not, allow 30-min. DT to terminate. Confirm CTh is 4°F above setpoint. After 30-min. DT terminates, does Comp icon turns on and Comp energize? If not, replace CB.

Legend: CB–control board; Comp–compressor; CT–cabinet temperature; DM–display module; DS–door switch; DT–defrost timer; EvapFM–evaporator fan motor

C. Thermistor Check

The cabinet thermistor is used for cabinet temperature control. Thermistor resistance varies depending on temperature. The control board monitors the resistance to control system operation. No adjustment is required. In the event the cabinet thermistor reading is out of range (Pr1 alarm), the compressor operates on a fixed time basis of 10-min. on and 10-min. off.

To check thermistor resistance, follow the steps below.

1)Press the power button for 2 sec. to turn the appliance off, then unplug the appliance.

2)Remove the evaporator shroud.

3)Disconnect and remove the evaporator thermistor.

4)Immerse the thermistor sensor portion in a glass containing ice and water for 2 to 3 min.

5)Check the resistance between the wires at the thermistor connector. Normal reading is within 14.0 to 19.0 kΩ. If outside the normal reading, replace the thermistor.

6)Reconnect and replace the thermistor in its correct position.

7)Replace the evaporator shroud in its correct position.

8)Plug the appliance back in. Press the power button for 2 sec. to turn the appliance on.

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