Sankyo Twist Tray Ice Maker

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Operation and Troubleshooting
Introduction:
The Twist-Tray Ice Maker (IM) is a 10 cube ice maker manufactured by Sankyo. It is a single
unit with no replaceable parts. The IM operates with DC voltages of 14VDC and 5VDC, and
water pressure between 30 and 120 psi. It produces around 3.5lbs of ice per day (4lbs per
day if MAX ICE is enabled).
IM timing and logic is controlled by the UI Core Control Board. The IM has the following
operational components (Figure 1):
• DC Motor with bi-directional movement
• Bail Arm to sense ice level in the ice bin
• Internal feedback switch to determine motor position
• Thermistor
The DC motor twists the ice tray. Ice is detached by the twisting motion, no heater is
needed. The motor also operates the bail arm.
The bail arm, and the internal feedback switch, checks if the ice bin is full.
The internal feedback switch helps determine if the ice bin is full and monitors motor shaft
position.
The thermistor senses the temperature of the ice tray to determine if the water is frozen.
(Below 8°F (-13°C) for Normal Ice, 5°F (-15°C) for Max Ice.
Figure 1: Sankyo Twist Tray Ice Maker
Thermistor
Bail Arm
DC Motor
and Internal
Feedback Switch
Ice Tray

Ice Maker Operation
The information in this section is available as a flow chart. See Attachment 1 – Ice Maker Normal Operation Flow Chart.
The IM has five standard states during normal operation. They are:
1. Homing
2. Filling
3. Freezing
4. Ice Ready
5. Harvesting
Other states include Homing Paused, Harvesting Paused, and IM Jammed.
Homing
When power is initially applied to the IM, it will enter the Homing state. 14VDC is applied to the motor driving it counterclockwise
(CCW). The internal feedback switch closes when the ice tray reaches the home (fill) position.
If the IM is not in the Home position after 45 seconds, the IM will enter the Jammed state. The IM will attempt Homing
every 60 minutes while in the Jammed state.
Filling
IM filling is skipped for the first cycle following a power interruption to the refrigerator. This ensures the IM is not
overfilled, and results in a 3 hour wait for the first batch of ice to drop.
For subsequent cycles, 115VAC is applied to the IM water valve solenoid for 15 seconds, filling the IM with 3.38 fl. Oz.
(100ml) of water.
The water fill tube has a heater to prevent icing of the fill tube following Filling. At the beginning of the Filling state, the fill
tube heater, if on, will be turned off. After filling completes, a 20 minute delay timer will begin. After these 20 minutes
pass, the fill tube heater will turn on for 90 minutes, or until the beginning of the next fill cycle, whichever comes first.
During periods where the IM is inactive (turned off, full ice bin, etc.) it is possible for the fill tube to freeze over. After the
IM becomes active again, it may take one or two cycles to thaw the ice maker inlet tube line.
Freezing
After the 15 second fill time, the IM enters the Freezing state until the ice cubes are ready. The ice cubes are ready after
time and temperature requirements are met. Time and temperature requirements vary between normal ice mode, and
MAX ICE.
In normal ice mode, the thermistor temperature must be at or below 8°F (-13°C). In addition, a minimum of 85 minutes
must pass. If the RC or FC door is opened during the Freeze state, the timer is paused until the door is closed and
additional time is added. For example, if the FC door is opened for 5 minutes, the timer stops for 5 minutes and 5 minutes
are also added to the 85 minute timer for a total of 95 minutes.
In MAX ICE mode, the minimum timer is decreased to 70 minutes, but the thermistor temperature must be at or below 5°F
(-15°C)

Page 3
Ice Ready
After the ice is ready the IM checks that the ice bin is present, the FC door is closed, and the ice bin is not full. If these
conditions are met, the IM enters the Harvesting state.
To check whether the ice bin is full, 14VDC is applied to the IM motor, driving it clockwise (CW).
The motor begins twisting the tray and lowers the bail arm. In the first 7 seconds, if the bail arm contacts ice the internal
feedback switch will close indicating the bucket is full. The DC motor will reverse direction, driving the ice tray counterclockwise
(CCW) back to the home position.
The IM will wait 60 minutes, and then repeat this process to check if the ice bin is still full. This process repeats until the
IM is not full.
When the ice bin is not full, the internal feedback switch will remain open during these first 7 seconds, and the IM will
enter the harvest state, while continuing to drive the IM in the CW direction.
Harvesting
During Harvesting, the position of the internal feedback switch indicates the position of the ice tray.
Since the ice bin is not full, the IM motor continues driving in the CW direction. The CW motion continues, twisting the ice
tray to a 160° rotation and dumping the ice. When the tray reaches 160° rotation, the internal feedback switch closes
indicating end of course for the ice tray. Travel from the home to end of course position takes between 14 and 20
seconds.
After reaching end of course, the polarity of the 14VDC is reversed, and the IM motor drives the tray in a CCW direction.
The internal feedback switch opens shortly after the IM motor begins moving in the CCW direction. The switch will close
again when the ice tray is back to the Home position. Travel from the end of course position, to Home takes between 13
and 19 seconds.
If the IM is not in the Home position after 45 seconds, the IM will enter the Jammed state. The IM will attempt Homing
every 60 minutes while in the Jammed state.
Harvesting Paused
During Harvesting, if the ice bin is removed, or the FC door is opened, Harvesting will pause and the IM will not move.
Harvesting will resume when the ice bin is present and the FC door is closed, provided the door was not open for more
than 60 minutes. If the door was open more than 60 minutes, the IM will enter Homing until thermistor freezing
temperature is satisfied. After the freezing temperature is satisfied, Harvesting will begin again.
Homing Paused
During Homing, if the ice bin is removed, or the FC door is opened Homing will be paused and the IM will not move.