Sub-Zero Built-In Series Assembly page 21

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Electronic Control System
Additional Regulating of Refrigerator Compartment Temperatures:
Details of Controlling the Refrigerator Variable Speed Evaporator Fan Motor
The evaporator fan in the refrigerator zone uses a low DC voltage variable speed motor. During normal operation
and when the door is closed, the motor is supplied with 12V DC at all times from P2-14 off of the control board, with
the neutral or ground return to P2-1. When high offset temperature is detected a command is sent to the evaporator
fan motor from P2-13 to run at high-speed, and the RPM is monitored via P2-16. On some models, the refrigerator
evaporator fan will always run at high speed when energized, while on others a command will be sent to the fan
after approximately thirty (30) seconds of high-speed operation to ramp down to low-speed. This will vary by model.
If the compartment thermistor in those models where the fan speed is normally ramped down after thirty (30) sec-
onds detects temperatures above high offset, the fan will remain at high-speed until the temperature falls below high
offset, then ramp down to low-speed. And, in all models, if the refrigerator door is opened while the evaporator fan
is operating, the microprocessor will detect the power signal to the lights and interrupts the 12V DC power to the fan.
(See Figure 3-40)
NOTE:
• During Sabbath Mode the lighting system is disabled and the 12V DC supplied to the evaporator fan cannot be
interrupted, thus the evaporator fan may be observed running when the door is open.
• If improper RPM signals are detected from the evaporator fan, the appropriate fault code will be logged.
LOW VOLTAGE
3. High-speed
command
sent to motor
NEUTRAL
(P2-13), after
L1
L1
30 seconds,
MAIN LIGHTS
low-speed
COMP1
COMP2
command
DEFROST HTR
sent to motor
(depending
on model)
1. 12VDC sup-
plied to
motor (P2-14)
Motor RPM
monitored at
all time (P2-16)
EXERNAL
DEVICE
KEYPAD
Figure 3-40. Signal Trace Schematic: Low DC Voltage Variable Speed Refrigerator Fan Operation
#7019014 - Revision A - October, 2010
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2. High offset temperature
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