Sub-Zero UC-15I Service Manual page 28

Theory of Operation
Harvest Cycle
During the last minute of the freeze cycle
the electronic control observes the temper-
ature detected by the the thermistor on the
liquid line (See Figure 3-9), then calculates
and controls proper harvest duration.
Once in a harvest cycle, the compressor
and condenser fan motor remain energized,
with the hot gas valve and water valve also
being energized, but the water pump is
switched off (See Figure 3-9).
During the harvest cycle the compressor
continues pushing refrigerant through the
sealed system, but with the hot gas valve
open, the high-pressure/high-heat gas from
the compressor is diverted to the evapora-
tor instead of the condenser. The water
valve is opened to pour water over the top
of the evaporator and into the reservoir.
With the water pouring over the top of the
evaporator and the warm gas running
through the evaporator, the ice cubes
release from the cube molds and fall into
the storage bin.
NOTE: Minimum harvest cycle is 60 sec-
onds.
NOTE: If a problem with the
water system is encountered,
it is more likely to lead to
issues during the harvest
cycle before causing any
freeze issues.
NOTE: The Water System
During Harvest Cycle -
Approximately three quarts of
water are added to the reser-
voir during the harvest cycle,
over-filling the reservoir by
approximately one quart.
The extra quart of water rins-
es the reservoir and goes
down the drain carrying the
mineral impurities.
#7012423 - Revision A - August, 2009
Model UC-15I (Undercounter Ice Machine)
Compressor (ON)
Figure 3-10. Refrigeration and Water System Diagram - Harvest Cycle
FUSE
CONTROL BOARD
BIN
THERMOSTAT
(CLOSED)
Figure 3-9. Wire Diagram - Harvest Cycle
Cubes Release
from Molds
Water Inlet Tube
Water Valve
(OPEN)
Condenser Fan (OFF)
3-8
COMPRESSOR
HOT-GAS
HARVEST VALVE
CONDENSER
FAN MOTOR
LIQUID LINE
THERMISTOR
WATER VALVE
Evaporator
(Warm Gas
Circulating)
Circulating
Pump
(OFF)
Reservoir
Drain
Over Fills
Hot Gas Valve
(OPEN)