Service Diagnosis; 10-Minute Diagnostic Procedure - Hoshizaki KM-251BAH Service Manual

IV. Service Diagnosis
A. 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 70°F or warmer air and 50°F 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. Check for voltage at the 10-pin connector.
1) Turn power off and access the control box and the electrical box.
2) Turn power on and place the control switch in the ICE position. The red LED on the
control board comes on. A 5 second delay occurs.
3) One Minute Fill Cycle – LED 4 is on. The freeze water valve is energized. After
1 minute, the control board checks for a closed lower float switch. If the lower float
switch is closed, the harvest cycle begins. If closed, continue to step 4. If the lower float
switch is open, the freeze water valve will remain energized through additional 1 minute
fill cycles until water enters the sump and the lower float switch closes (low water safety
protection during initial start up and at the end of each harvest). Diagnosis: If the
freeze 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 lower float switch or bad 1 minute timer in board.
4) Initial Harvest Cycle – LEDs 1, 4 and 2 are on. The freeze water valve de-energizes
and the hot gas valve energizes (also energizing the water valve relay), the harvest
water valve energizes, and the contactor coil energizes to start the compressor.
The evaporator warms and the thermistor senses 48°F (9°C). The control board then
receives the thermistor's 3.9 kΩ signal and turns operation of harvest over to the
harvest timer. The timer completes counting (1 to 3 minutes – S4 dip switch 1 & 2).
The unit then cycles to freeze. The harvest water valve is open during harvest for a
maximum of 6 minutes or the length of harvest minus 50 seconds, whichever is shorter.
The pump motor energizes and runs for the last 50 seconds of harvest. Diagnosis:
Check if compressor is running, hot gas valve is open, harvest water valve open. If
these are okay, next check for at least 48°F (9°C) on the suction line. If cooler, check
for inlet water too cold or expansion valve stuck open. If the suction line is at least
48°F (9°C), disconnect the thermistor at the board (K3) and check for resistance of
3.9 kΩ or less. If different, check and replace if necessary. See "II.C.3.b) Harvest
Control – Thermistor," for check procedure. If resistance is 3.9 kΩ or less, reconnect
the thermistor to the board. If harvest does not terminate within 3 minutes, replace the
board.
5) Freeze Cycle – LED 1 is on. The compressor and pump motor remain energized and
the fan motor energizes. The hot gas valve de-energizes (also de-energizing the water
valve relay) and the harvest water valve de-energizes. The unit is held in freeze by a
5 minute short cycle protection timer. After 5 minutes, the freeze cycle operation is
transferred to the lower float switch for freeze termination. During the first 5 minutes
of freeze, confirm that the evaporator temperature drops. After 7 minutes in freeze,
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