Electronic Control System
Under Counter (UC-24) Series
3-16
#7003933 - Revision B - November, 2007
Monitor and Control Freezer “Adaptive Defrost” (UC-24C Only)
Initially, the compressor will cycle-run for 12 hours, after which the microprocessor sends a signal to the defrost relay
on the control board to close. This supplies power to the defrost heater. At the same time the compressor, con-
denser fan and evaporator fan are switched off.
With the “Adaptive Defrost” technique, the length of time that the defrost heater stays on to open the defrost termina-
tor bimetal (70°F/21°C), is observed by the microprocessor via the grey w/white stripe wire to J2.
The microprocessor then determines the number of hours before the next defrost. If the heater stays on for a short-
er time than specified, the microprocessor increases the next defrost interval. If the heater stays on longer than
specified, the electronic control decreases the next defrost interval. (See Figure 3-22) This is an ongoing process
whereby the defrost time and the defrost interval will vary by unit use.
NOTES:
• A five (5) minute time delay/dwell follows all defrosts. At the end of the five (5) minute dwell, the compressor and
condenser fan are energized, but the evaporator fan will not be energized until the evaporator temperature falls
below 35°F (2°C).
• The minimum defrost interval is six (6) hours of compressor run time; the maximum defrost interval is eighty (80)
hours of compressor run time; the maximum defrost duration is twenty-five (25) minutes plus five (5) minute dwell.
• If the grey w/white wire defrost sensing line is open, defrost operation defaults to twenty-five (25) minute defrost
time and 6 hour build time, and Error Code 22 is logged. If the evaporator thermistor detects an underheat or
overheat situation at the same time, Error Codes 20 or 23 will be registered, respectively.
• During defrost, the display temperature is locked.
Figure 3-22. UC-24C Signal Trace Schematic - Adaptive Defrost
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