Service Diagnosis; 10-Minute Km Diagnostic Procedure - Hoshizaki KM-1800SWH/3 Service Manual

IV. Service Diagnosis
A. 10-Minute KM 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.
) Turn power on and place the control switch in "ICE" position. A 5 second delay occurs.
3) One Minute Fill Cycle – The inlet water valve is energized. After 1 minute, the control
board checks the float switch. If the float switch is closed, the unit cycles to harvest. If
closed, continue to step 4. If the float switch is open, the unit repeats the 1 minute fill
cycle until water enters and the 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 – Inlet 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 kΩ signal and turns operation of 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, water
valve still open. Average harvest cycle at factory setting is  to 3 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 – Compressor remains energized, pump motor, (line valve on remote
condenser unit), and fan motor energize. The inlet water valve and hot gas valve de-
energize. The unit is held in freeze by a 5 minute short cycle protection timer. After
the 5 minute short cycle protection timer terminates, the freeze cycle operation is
transferred to the float switch for freeze termination. During the first 5 minutes of freeze,
confirm that the evaporator temperature drops. After 7 minutes in freeze, remove the
black float switch lead from the K5 connector. The unit should immediately switch to the
pump-out cycle. Diagnosis: If the evaporator is not cold, check to see if the hot gas
valve is still open or if the expansion valve is not opening properly, if the water valve
is continuing to fill the reservoir, if there are improper unit pressures, an inoperative
compressor, or an inoperative headmaster (C.P.R.) (remote condenser unit only). If the
unit remains in freeze with the float switch removed, replace the board.
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