Service Diagnosis; Minute Diagnostic Procedure - Hoshizaki KMD-410MWH Service Manual

IV. SERVICE DIAGNOSIS

1. 10-MINUTE DIAGNOSTIC PROCEDURE

The 10 minute check out procedure is basically a sequence check which can be used at
unit start-up or for system diagnosis. Using this check out procedure will allow you to
diagnose electrical system and component failures in approximately 10 minutes under
normal operating conditions of 21°C or warmer air and 10°C or warmer water
temperatures. Before conducting a 10 minute checkout, check for correct installation,
proper voltage per unit nameplate and adequate water supply. As you go through the
procedure, check to assure the components energize and de-energize correctly. If not,
those components and controls are suspect.
1) Turn power off and access the control box. Clear any ice from the bin control actuator
located in the bin.
2) Turn power on and place the control switch in the "ICE" position. A 5 second delay occurs.
The "POWER OK" LED on the control board comes on. If the "POWER OK" LED is
flashing (indicating a full bin), check the bin control. See "II. 6. [b] BIN CONTROL CHECK
PROCEDURE."
3) One Minute Fill Cycle – The harvest water valve is energized. After 1 minute, the control
board checks the float switch. If the lower float switch is closed, the unit cycles to harvest.
If closed, continue to step 4. If the lower float switch is open, the unit repeats the 1 minute
fill cycle until water enters and the lower float switch closes (low water safety protection
during initial start up and at the end of each harvest). Diagnosis: If the water valve does
not open, check for no supply voltage at water valve terminals, bad coil, or plugged
screen or external filter (no water flow). If unit fails to start harvest, check for open float
switch or bad 1 minute timer in board.
4) Initial Harvest Cycle – The harvest water valve remains energized, contactor coil
energizes to start the compressor (and fan motor on a remote condenser unit), and the
hot gas valve energizes. The evaporator warms and the thermistor senses 48 °F (9°C).
The control board then receives the thermistor's 3.9 k
harvest over to the harvest timer. The timer completes counting (1 to 3 minutes). The unit
then cycles to freeze. Diagnosis: Check if compressor is running, hot gas valve is open,
harvest water valve still open. Average harvest cycle at factory setting is 2 to 4 minutes.
How long does initial harvest last? 1.5 minutes after initial harvest begins, touch the
compressor discharge line. Is it hot? If not, check refrigerant pressures and compressor
operation. If it is hot, touch the inlet line to the evaporator. Is it hot? If it is hot and the
freeze cycle is not starting, check the harvest timer adjustment, the thermistor for open
circuit, the discharge line temperature, compressor efficiency, and if the hot gas valve is
fully open.
5) Freeze Cycle – The compressor remains energized, pump motor, (line valve if applicable),
and fan motor energize. The harvest water valve and hot gas valve de-energize. The unit
is held in freeze by a 5 minute short cycle protection timer which starts after the
thermistor temperature reaches 2°C. After this period, the freeze cycle operation is
transferred to the float switch for freeze termination. The lower float switch activates
(open) 2 times during the course of a freeze cycle; the first is for refill, the second is for
freeze termination. After the second lower float switch activation, the control board
terminates freeze and initiates harvest.
signal and turns operation of
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