Operating Systems - Whirlpool KDDC24RVS Technical Education

As the usual start up, the main PCB turns
on the condenser fan and after 10 seconds
the compressor will start. The compressor
will continue to run until the temperatures of
both thermistors reach the set temperature
for each chamber of -4ºF (the number 4 is
subject to design change). While the com-
pressor is on, the main PCB turns only one of
the two evaporator fans on. The evaporator
fan in the lower chamber is turned on primar-
ily, as the lower chamber is a freezer (about
0ºF) and the upper chamber is a refrigerator
(4ºF). When the lower thermistor tempera-
ture reaches to the freezer set temperature
of -4ºF, the lower evaporator fan motor stops,
and logic reads the upper thermistor temper-
ature. If it is higher than the refrigerator set
temperature of -4ºF the main PCB will turn
on the upper evaporator fan and continue to
run the compressor. Normally, this switching
between upper and lower evaporator fans re-
peats several times before both temperatures
reach below the set temperature of -4ºF.
Once the temperatures of both thermistors
reach below the set temperature of -4ºF, the
main PCB shuts off the compressor and both
evaporator fans. Main PCB will turn off the
condenser fan 2 minutes later.
When the temperature of the thermistor of
upper chamber (refrigerator) reaches the
refrigerator set temperature of 4ºF, but the
freezer thermistor temperature remains
below the freezer set temperature 4ºF, the
main PCB will turn on the upper evaporator
fan without turning the condenser fan or the
compressor. Basically, cooling logic is us-
ing the cold air of the freezer section to cool
the refrigerator section during this period.
If the thermistor temperature of the upper
chamber (refrigerator) reaches the refrigera-
tor set temperature -4ºF while the thermistor
temperature of the lower chamber (freezer)
is still lower than the freezer set temperature
4ºF (and this seems to happen regular basis),
the main PCB will simply turns off the upper
evaporator fan without ever turning the com-
pressor on.
OPERATING SYSTEMS (continued)
If the thermistor temperature of the lower
chamber (freezer) reaches to the freezer set
temperature of 4ºF, the main PCB will turn on
the condenser fan, then the compressor and
the lower evaporator fan (10 seconds later)
regardless to the temperature of the thermis-
tor in the upper chamber. While the com-
pressor is on, the above switching between
two evaporator fans takes place again.
In a rare case (for example, at the beginning
of ice making or the ambient temperature is
very high) when the compressor is on and
the temperature of the lower thermistor is
kept above the freezer set temperature -4ºF
for extended period due to higher then nor-
mal demand in the freezer section, the main
logic monitors the temperature of the upper
chamber every 10 minutes or so to make
sure the refrigerator temperature is within
the range. If not, shut off the lower evapora-
tor fan and turn on the upper evaporator fan
until the temperature of the upper thermis-
tor drops to the refrigerator set temperature
-4ºF. Once the upper thermistor temperature
reaches that, the lower evaporator fan will be
switched on.
3) General Defrost Operation (All
Models)
The main PCB has a timer to monitor the ac-
cumulated compressor operation time. When
this time reaches certain hours (for example 10
hours), the main PCB will shut off the compres-
sor the evaporator fans, reset the timer, and stop
sampling the temperature. In 30 seconds, the
defrost heater will turn on and the condenser fan
will be turned off 2 minutes after the shut off of
the compressor. The heater will be cut off when
the defrost-sensing thermistor that is mounted
near the top center of the evaporator pipe has
reached the preset temperature (for example
8ºF). (If the defrost-sensing thermistor logic
fails, then the fuse will melt as any redundantly
protected refrigeration system.) Five minutes
after termination of the heater, the main PCB
starts to sample the temperature and the same
cooling function above 1) or 2) resumes.
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