Subzero IC-24CI Service Manual page 12

Controls and Operation
FAN-ASSISTED OFF-CYCLE DEFROST
If the refrigerator compartment temperature reaches high offset
but the refrigerator evaporator temperature is too low for the
refrigerator compressor to start, the control board sends a high-
speed run signal to the refrigerator evaporator fan. This sends
warm air across the refrigerator evaporator, causing the
evaporator temperature to rise. Once the refrigerator evaporator
temperature rises to the set point required by the control board,
the control board starts the compressor.
▪ If the control board senses that the refrigerator
compartment temperature is below 36°F, it will extend the
defrost time before starting the evaporator fan.
▪ If the refrigerator compartment thermistor is shorted or
open, an EE displays on the UIM, the service wrench icon
flashes, and a fault code is logged. The refrigerator
compressor defaults to 20 minutes on and 40 minutes off.
▪ If the refrigerator evaporator thermistor is sensed as being
shorted or open, an EE is visible in the Service Options -
Temps screen, the service wrench icon flashes, and a fault
code is logged. The refrigerator compressor does not start
until the refrigerator compartment thermistor reads 37°F
above high offset.
▪ In Sabbath mode, the refrigerator compartment thermistor
still controls the refrigerator compressor, except a random
15 to 25 second delay occurs before the cooling cycle
starts.
FREEZER ADAPTIVE DEFROST
With Adaptive Defrost, the control board monitors the length of
time the defrost heater stays on to reach the set temperature at
the evaporator thermistor. Initially, the freezer compressor runs
for six hours, then the compressor and evaporator fan switch
off, and the control board defrost relay closes, supplying power
to the defrost system. After the initial pull-down, the control
board uses the length of time to calculate the number of hours
before the next defrost interval. During Adaptive Defrost, the
control board prevents the freezer temperature displayed on the
UIM from changing.
▪ If the heater energizes for a shorter time period than the
control board estimates based on predetermined
algorithms, the control board increases the next defrost
interval.
▪ If the heater energizes for a longer time period, the control
board decreases the next defrost interval.
▪ Adaptive defrost is an ongoing process where the defrost
heater on-time and the defrost interval vary by unit use.
▪ Minimum defrost interval is six hours of compressor run
time.
▪ Maximum defrost interval is 80 hours of compressor run
time.
▪ Maximum defrost duration is 30 minutes, plus a five-minute
dwell time.
▪ If the defrost sensing line is open, the service wrench
flashes, a fault code logs, and the control board defrosts
the unit for 25 minutes after every six hours of freezer
compressor run time.
7041389 REVA 06/2017
ICE MAKER MONITORING
EXCESSIVE COMPRESSOR RUN
The control board monitors the position of the compressor
relays to determine the amount of time the compressor runs.
To clear fault indicators and fault codes, correct the problem
and clear the faults from the Service Options screen on the
UIM. Failure to clear fault codes results in the highest priority
fault indicator reappearing on the UIM when the unit is turned
back on.
COMPRESSOR RUN
Compartment If
Compressor runs
Refrigerator four hours, five
consecutive times
Compressor runs
Freezer six hours, five
consecutive times
▪ 24 hours of
▪ Compartment
Refrigerator or
Freezer
▪ Door/drawer is
▪ Unit is switched
13
IC-24C(I)
service.subzero.com
Then
▪ Fault code
logged
▪ Defrost initiated
▪ Service wrench
flashes
▪ Fault code
logged
▪ Defrost initiated
▪ Service wrench
flashes
100% run
▪ Service wrench
temperature still
flashes
higher than the
average of set
▪ Alarm sounds
point and low
▪ Compressor will
offset
not energize for
temperature
at least three
minutes to
not opened
protect
during last run
electricals
period
off then back on