Jenn-Air JB36NXFXLW00 Technical Education page 38

AIR DOOR
The air door is driven by a reversible DC stepper
motor. The motor operates on a 12 vdc, peak-
to-peak square wave. Voltage is delivered to
the air door in a series of short pulses. It is not
possible to obtain a reliable voltage reading
with a VOM.
Separate windings are used to move the air door
open or closed. The door can be in any position
from 0 to 90 degrees. The air door is used to
fine-tune the airflow to the refrigerator.
The refrigerator temperature determines the
opening of the air door. When the refrigerator
requires cooling, the air door partially opens,
and then adjusts, if necessary. While the re-
frigerator is cooling, the door will be adjusting
continuously to maintain or recover refrigerator
temperature.
ADAPTIVE DEFROST
The adaptive defrost control function of the main
electronic control board allows the refrigerator
to enter a defrost mode only when it is needed.
When powered up for the first time, the control
initiates a defrost cycle after 8 hours of com-
pressor run time. By monitoring the duration
of defrost heating time and compressor run
time, the control will continuously adapt the
time between defrosts to optimize efficiency.
Time between defrost periods will vary between
8 and 100+ hours.
Defrost will occur immediately when the com-
pressor has run at 3990 rpm or greater for 1 hour,
and 8 hours have elapsed since the last defrost.
PULSED DEFROST
For the first 2 minutes of defrost, the heater is
on continuously. It will then cycle off for 1 min-
ute, and back on for 2 minutes. The heater will
continue to cycle at this ratio until the bimetal
opens, or until 33 minutes has elapsed. At this
point, heat is discontinued, and a 4-minute "drip
time" begins. This allows the water to drain be-
fore the refrigerator returns to a cooling mode.
Maximum defrost time, (pulsed heat on/off time
+ drip time) is 37 minutes.
When entering a defrost cycle, if the bimetal
is open, the time to defrost is reset to 8 hours,
and the control will time through the entire
37-minute defrost period. The time to defrost
can be reset to 8 hours manually by holding
"set to recommended" for 5 seconds. During
diagnostics this will allow a technician time to
look for heater operation, and if necessary,
bypass the bimetal.
POWER INTERRUPTION
After a power interruption, the following events
will occur:
• The refrigerator returns to the same operating
mode and settings in use prior to the power in-
terruption. If the unit was off, it remains off.
• Initially, the compressor, evaporator fan, and
condenser fan motors will be off.
• The air door will close, and then adjust to the
proper opening. The evaporator fan starts
when the air door opens.
• The adaptive defrost control resets the
compressor run time counter to 0, and if the
freezer is above 20°F, the time to defrost is
set to 8 hours.
• If the freezer temperature is below 14
(–10° C), the compressor may start after a
delay of 7 minutes. If the freezer tempera-
ture is above 14°F, the compressor starts
immediately.
• The Main Control Board board supplies 14
volts DC to the mullion heater when both
refrigerator doors are closed, Energy Saver
mode is turned off, and Holiday mode is
turned off.
FAILURE DEFAULTS
In the event of a thermistor, or keypad failure,
the main electronic control board uses one of
the following default modes, which will continue
until the failure is corrected.
Refrigerator Thermistor
If the main electronic control board senses an
open or a shorted thermistor, the air door and
the evaporator fan motor will begin to operate
on a timed on and off cycle, based on current
selected temperature settings. The evaporator
fan motor will run when the air door is open.
At mid-settings of 37°F / 3°C, the air door will
open for 16 minutes, and close for 30 minutes.
Setting the freezer colder, or the refrigerator
warmer, will reduce the door-open time. Setting
the freezer warmer, or the refrigerator colder,
3-4
°F