Sequence Of Operation; One Minute Fill Cycle; Initial Harvest Cycle; Freeze Cycle - Hoshizaki KM-251BAH Service Manual

B. Sequence of Operation
The steps in the sequence are as outlined below. When power is supplied, the red LED
on the control board comes on. A 5 second delay occurs at startup. Note that the order
of the green LEDs from the outer edge of the board is 1, 4, 3, 2.

1. One Minute Fill Cycle

LED 4 is on. FWV opens and the fill period begins. After 1 minute, the board checks
for a closed LF/S. If LF/S is closed, the harvest cycle begins. If not, FWV will remain
energized through additional 1 minute cycles until water enters the sump and LF/S
closes. This serves as a low water safety to protect the water pump.

2. Initial Harvest Cycle

LEDs 1, 4 and 2 are on. FWV closes, HGV opens, water valve relay energizes and HWV
opens, Comp energizes, and harvest begins. The control board monitors the warming
of the evaporator via the thermistor located on the suction line. When the thermistor
reaches 48°F (9°C), the control board reads a 3.9 kΩ signal from the thermistor and
turns harvest termination over to the adjustable harvest timer which is factory set for
normal conditions. The timer has settings of 60, 90, 120, and 180 seconds (S4 dip switch
1 & 2). When the harvest timer completes its count down, the harvest cycle is complete
and the freeze cycle starts. The minimum total time allowed by the board for a complete
harvest cycle is 2 minutes. HWV is open during harvest for a maximum of 6 minutes or
the length of harvest minus 50 seconds, whichever is shorter. PM energizes and runs
for the last 50 seconds of harvest. At the end of harvest, the control board checks the
position of LF/S and proceeds to the freeze cycle if it is closed or calls for a 1-minute fill
if it is open.

3. Freeze Cycle

LED 1 is on. Comp and PM continue to run, FMS energizes, HGV closes, water valve
relay de-energizes and HWV closes, and the freeze cycle starts. For the first 5 minutes
the control board will not accept a signal from LF/S. This 5 minute minimum freeze acts
as a short cycle protection. At the end of 5 minutes, LF/S assumes control. As ice builds
on the evaporator, the water level in the sump lowers and UF/S opens. 15 seconds after
UF/S opens, FWV opens (LED 4 is on when FWV is open) and allows water in. After
UF/S closes again, FWV closes 3 seconds later. This continues until the tank has refilled
the number of times determined by the refill counter (S5 dip switch is factory set - do not
adjust). The KM-251BAH refills 9 times. After the final refill, the freeze continues until
LF/S opens and terminates the freeze cycle.
Note: After the first freeze following startup and every 10th cycle thereafter, LEDs 1, 3,
and 2 come on between freeze and harvest. Comp continues to run, HGV opens
and FMS de-energizes. PM stops for 2 seconds. PM restarts and runs for 10
seconds.

4. Normal Harvest Cycle

LEDs 1, 4 and 2 are on. Comp continues to run, HGV opens, water valve relay energizes
and HWV opens. As the evaporator warms, the thermistor reaches 48°F (9°C). The
control board then receives the thermistor's 3.9 kΩ signal and starts the harvest timer.
When the harvest timer completes its count down, the harvest cycle is complete and
the next freeze cycle starts. The minimum total time allowed by the board for a complete
harvest cycle is 2 minutes. HWV is open during harvest for a maximum of 6 minutes or
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