Freezer "Adaptive Defrost - Sub-Zero 700TC-3 Service Manual

Integrated
Integrated
Monitor and Control Freezer "Adaptive Defrost"
Initially the freezer compressor will cycle-run for twelve hours (twenty-four hours in the model 700TF/I-3), after which
the microprocessor sends the signal to the defrost relay on the control board to close. This supplies power to the
defrost heater, and the compressor is switched off (See Figure 3-24). With the "Adaptive Defrost" technique, the
length of time that the heater actually stays on to defrost the evaporator and satisfy the defrost terminator is
observed by the microprocessor. The microprocessor then determines the number of hours before the next defrost.
If the heater stays on for a shorter 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. This is an ongoing
process whereby the defrost time and the defrost interval will vary by unit use.
NOTE: A five (5) minute time delay/dwell follows all defrosts, except in the model 700TF/I-3 where the delay/dwell is
ten (10) minutes. The drain trough heater is energized during defrost and the delay/dwell period.
NOTE: The minimum defrost interval is six (6) hours; The maximum defrost interval is eighty (80) hours; the maxi-
mum defrost duration is twenty-five (25) minutes.
NOTE: If the defrost sensing line is open, defrost operation defaults to 25 minute defrost time / 6 hour build time,
and Error Code 22 is logged. If the evaporator thermistor detects an under-heat or overheat situation at the same
time, Error Codes 20 or 23 is logged, respectively.
NOTE: During defrost, the displayed temperature is locked.
HIGH VOLTAGE
BLACK
J5
J7
E2 E7 E10 E6
J3
J4
J1
J2
Figure 3-24. 700TC/I-3 Signal Trace Schematic (High Voltage) of Freezer Adaptive Defrost
3
3
(700- T ALL)
(700- T ALL)
115 VOLTS
L1 NEUT
60 CYCLES
WHITE
J6
GRAY/WHITE
DEFROST
BLUE TERMINATOR
Series
Series Electronic Control System
WHITE
M
M
Length of defrost time moni-
tored by microprocessor via
defrost sense line
30-38 OHMS
155-175 OHMS
M
3-15
#3758412 - Revision B - December, 2006
M
M
DEFROST
HEATER
DRAIN TROUGH
HEATER
Drain trough
heater energized
during defrost and
delay/dwell period