Hoshizaki KM-900MAH Service Manual page 17

2) Defrost Timer
The defrost cycle starts when the Float Switch opens and completes the freeze cycle.
But the Defrost Timer does not start counting until the Thermistor senses 48°F at the
Evaporator outlet. The period from the end of the freeze cycle up to the point of the
Thermistor's sensing varies depending on the ambient and water temperatures.
3) High Temperature Safety - 127 ± 7°F
The temperature of the suction line in the refrigerant circuit is limited by the High
Temperature Safety.
During the defrost cycle the Evaporator temperature rises. The Thermistor
senses 48°F and starts the Defrost Timer. After the Defrost Timer counts down
to zero, the normal freeze cycle begins. If the Evaporator temperature continues
to rise, the Thermistor will sense the rise in temperature and at 127 ± 7°F the
Thermistor operates the High Temperature Safety.
This High Temperature Safety shuts down the circuit and the icemaker automatically
stops.
This High Temperature Safety protects the unit from excessive temperature. The Control
Board will Beep every 3 seconds. The white Reset Button on the Control Board must be
pressed with power on to reset the Safety.
4) Low Water Safety
If the Pump Motor is operated without water, the mechanical seal can fail. To prevent
this type of failure, the Controller Board checks the position of the Float Switch at the end
of the initial one minute water fill cycle and at the end of each defrost cycle.
If the Float Switch is in the up position (electrical circuit closed), the Controller Board
changes to the ice making cycle. If the Float Switch is in the down position (electrical
circuit open), the Controller Board changes to a one minute water fill cycle before starting
the ice making cycle. This method allows for a Low Water Safety shut down to protect
the Water Pump from mechanical seal failure.
For water-cooled model, if the water is shut off, the unit is protected by the High Pressure
Switch.
5) High Voltage Cutout
The maximum allowable supply voltage of this icemaker is limited by the High Voltage Cutout.
If miswiring (especially on single phase 3 wire models) causes excessive voltage on the
Controller Board, the High Voltage Cutout shuts down the circuit in 3 seconds and the
icemaker automatically stops. When the proper supply voltage is resumed, the icemaker
automatically starts running again. The Control Board will signal this problem using 7 Beeps
every 3 seconds.
6) LED Lights and Audible Alarm Safeties
The red LED indicates proper control voltage and will remain on unless a control voltage
problem occurs. At startup a 5 second delay occurs while the board conducts an internal
timer check. A short beep occurs when the power switch is turned ON or OFF.
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