Automatic Defrost Operation; Air Circulation Patterns - Frigidaire FFBN1721TV0 Technical & Service Manual

Phase II of display panel self-inspection:
Display icon is lit up from left to right by each section in turn, with
interval time of 0.5 seconds. The display order is as follows:
Refrigerating icon, radar icon, freezing icon, close icon, minus
sign will be shown on the 8-digit display in turn in the order of a,
b, c, d, e, f, g, child-lock icon, Celsius icon, quick refrigerating
icon, quick freezing icon, smart icon, displaying the display board
version number, and waiting for 2seconds to display the version
number of the main control board.
Phase III of display panel self-inspection:
When the button is pressed, the display board displays its value.
• A - Refrigerating button - 1
• B - Freezing button - 2
• C - Mode pushbutton - 3
• D - Lock key - 4
3. Exiting self-inspection
Self-inspection will start timing, and the display panel will exit the
self-inspection function after 1 minute, and then enter the normal
operation mode.

Automatic Defrost Operation

Automatic defrost refrigerators operate on the principle that
moisture or frost transfers or migrates to the coldest surfaces
(evaporator) in the freezer compartment. For example, a small
amount of water spilled in the freezer compartment will freeze
immediately. However, this ice in time will evaporate and transfer
to the colder surfaces of the freezer such as the evaporator coil.

Air Circulation Patterns

Automatic defrost models have a single evaporator in the freezer
compartment, and have forced air cooling in the freezer and
fresh-food compartments. The "fin and tube" aluminum type
evaporator is located behind the back wall of the freezer
compartment. A circulating fan (suction type) pulls air from the
freezer compartment through the grill in the bottom of the freezer
and from the fresh-food compartment through a grill located in
each bottom rear corner of the food compartment cabinet
interior. The air is than drawn up through the fin and tubes of the
evaporator surface. The cold air is forced into a fan cover and
discharged into the top of the freezer. (See below figure.)
The air circulating fan operates any time the thermistors sense
the temperature of the food compartment or the freezer compart-
ment are above the upper control limit and send the information
to the lower control board. If the food compartment is calling for
cooling the automatic damper in the back air channel behind the
crisper drawer of the food compartment will open and allow cold
air to enter the food compartment.
Service Manual - Four-door Refrigerator (FFBN1721TV0 )
Function & Operation
The air is then carried up the air channel to the top and
discharges into the top of the food compartment. If the food
compartment calls for cooling but the fan is not running, the fan
will start as soon as the damper is open, and will continue to run
as long as the food compartment and/or the freezer compart-
ment calls for cooling. The freezer thermistor will stop the
compressor if the freezer compartment goes below the lower
control limit and restart the compressor on low speed as soon as
the temperature in the freezer goes back into the normal
operating range.
The air circulating fan is a 12 V DC fan motor that operates any
time the food compartment or the freezer compartment calls for
cooling. During the defrost period, the compressor and circu-
lating fan do not operate. The power board, located under the
freezer behind the grill, opens the electrical circuit to the fan
motor and compressor for the defrost cycle. The lower control
board also closes the damper door that is controlled by a 12 V
DC stepper motor, and keeps the damper door closed during the
complete defrost cycle.
If the product is equipped with a perfect temperature drawer, it
will pull air from the freezer through a small opening in the right
side of the bottom of the liner, just in front of the air return
opening. A fan controlled by the electronic drawer control will pull
the air up from the freezer through the drawer and the air will
return to the freezer by way of the right air return opening in the
liner.
Fan
Evaporator
Fan
Evaporator
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