Service Diagnosis; 10-Minute Km Diagnostic Procedure - Hoshizaki KM-515MAH 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 (21°C) or warmer air and 50°F (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. Check the
S4 dip switch settings to assure that they are in the factory default position. For factory
default settings, see "II.C.3.a) Default Dip Switch Settings." 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 the "ICE" position. A 5 second delay
occurs. The red "POWER OK" LED on the control board comes on.
3) One Minute Fill Cycle – LED 4 is on. 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 inlet
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 control board.
4) Initial Harvest Cycle – LEDs 1, 4, and 2 are on. The inlet water valve remains
energized, the contactor coil energizes to start the compressor (and fan motor on a
remote air-cooled unit), and the hot gas valve energizes. The inlet water valve is open
during harvest for a maximum of six minutes or the length of harvest which ever is
shorter. 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. When the harvest timer is complete, the freeze cycle starts. Diagnosis:
Check if compressor is running, hot gas valve is open, inlet 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.
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