Sub-Zero UC-24 series Service Manual page 17

Under Counter (UC-24) Series
Monitor and Control Refrigerator Fan-Assisted, Off-Cycle Defrost (UC-24B, UC-24R, UC-24RO)
Temperature signals from the compartment and evaporator thermistor's are observed by the microprocessor. During
off cycle defrost, if a refrigerator compartment temperature reaches high offset (calling for cooling) before evaporator
temperature rises to 38°F (3°C), no power will be supplied to the compressor. But, the evaporator fan will be
switched ON. Once the evaporator temperature reaches 38°F (3°C), normal cooling functions begin. (See Figure 3-
23).
NOTES:
• If refrigerator compartment thermistor is faulty, compressor operation defaults to twenty (20) minutes ON, forty (40)
minutes OFF cycling; EE appears in right of LCD; SERVICE will flash and Error Code 05 will be logged.
• If evaporator thermistor is faulty, the compressor will not energize until zone air temperature exceeds high offset
by 5°F (3°C); SERVICE flashes and Error Code 06 is logged.
• When in Sabbath Mode, the refrigerator compartment thermistor still controls compressor operation, except there
is a random fifteen (15) to twenty-five (25) second delay before the compressor is energized.
LOW VOLTAGE SCHEMATIC
DISPLAY
4. Evap Thermistor
below 38°F (3°C).
1. Compartment thermistor at high
off-set temp. calling for cooling.
HIGH VOLTAGE SCHEMATIC
ORANGE
J2
PIN 1
MAIN BOARD
PIN 1
J6
J4
PIN 1
PIN 1
J5
Figure 3-23. UC-24B Signal Trace - Refrigerator Fan Assisted Off-Cycle Defrost
MEMBRANE KEYPAD
PIN 1
DISPLAY BOARD
THERMISTOR
EVAPORATOR
THERMISTOR
REFRIGERATOR
115 VOLTS
60 CYCLES
L1 NEUTRAL
P4 WHITE
P3 BLACK
PURPLE
P1
P2
PIN 1
J3
ORANGE
REF LIGHT
SWITCH
ORANGE
Electronic Control System
J2
PIN 1
YELLOW
J3
RED
WHITE
BLUE W/RED STRIPE
ORANGE W/RED STRIPE
BLUE W/BLACK STRIPE
BLUE W/BLACK STRIPE
REF LIGHT SWITCH
PINK
LIGHT TUBE SWITCH
(UC-24B ONLY)
WHITE
5. Compressor and condens-
er fan stay OFF until evap
rises to 38°F (3°C).
OVERLOAD
PROTECTOR COMPRESSOR
M
CONDENSER FAN
RED
3. Evap fan energized.
REF (TOP)
LIGHT
2. Door is closed, so no power to lights.
This is monitored via the orange wire.
3-17
J2
P4
PIN 1
P3
MAIN BOARD
P1
P2
PIN 1
J6
ORANGE
J4
PIN 1
PIN 1
PIN 1
J5
WHITE
LIGHTS
WHITE
RUNNING
CAPACITOR
(WHEN
USED)
COMPRESSOR
STARTING
M
RELAY
M
REF FAN MOTOR
#7003933 - Revision B - November, 2007
J3