Hoshizaki KM-501MRH, KM-501MWH, KM-501MAH IV. Service Diagnosis Minute KM Diagnostic Procedure

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.

2)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 2 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 5 minutes, 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

33