How A Refrigerator Works
Years ago, all refrigerators had to be defrosted manually. You would turn the
refrigerator off, open the door(s), and allow any frost build-up to melt. When
the frost had completely melted away, you would turn the refrigerator back on.
Today, all but the smaller, apartment-sized refrigerators are self-defrosting.
Self-defrosting means what it implies--though frost continues to accumulate
inside the refrigerator, it melts automatically. The self-defrosting system has
three functional components:
Defrost timer
Defrost heater
Defrost thermostat
Defrost timer
The timer is like a clock. It continually advances, 24 hours a day. Every 6 to 8
hours, the timer turns off the cooling system of the refrigerator and turns on
the defrost heater.
Defrost heater
The defrost heater is similar to the burners on an electric stove. It's located
just beneath the cooling coils, which are concealed behind a panel in the
freezer compartment. The heater gets hot. And, because it's close to the cooling
coils, any ice or frost build-up melts. As the frost and ice melt, the
resulting water drips into a trough. The trough is connected to a tube that
drains the water into a shallow pan at the bottom of the refrigerator. The water
is then evaporated by a fan that blows warm air from the compressor motor over
the pan and out the front of the refrigerator.
Defrost thermostat
The process ends after either the amount of time specified on the timer or when
the defrost thermostat near the cooling coils senses that the heat near the
coils has reached a specific temperature.
You'll more quickly understand refrigerator cooling systems if you think of
their action as "removing heat from the air in the refrigerator" rather than
"cooling the air in the refrigerator." All residential refrigerators work on the
same principal for cooling. They all have:
A Compressor
A Condenser
A
Metering Device (Capillary Tube)
An Evaporator
Compressor
The compressor is the motor (or engine) of the cooling system. In built-in
refrigerators the compressor is located on top of the refrigerator behind a
grill or grate. In all other units it's normally at the bottom of the
refrigerator in the back. It's almost always black and about the size of a
football. If the refrigerator is self-defrosting, the compressor may be behind a
thin panel. The compressor runs whenever the refrigerator thermostat calls
for cooling (and the defrost timer is not in a defrost cycle, for
self-defrosting units). It is normally very quiet. When running, it is
compressing a refrigerant that is in a low-pressure gaseous state to a
high-pressure gas.
Condenser
The condenser is a series of tubes with fins attached to them, similar to a
radiator. It's always somewhere on the outside of the refrigerator. It may be:
1. A large black grid mounted to the back of the refrigerator
2. Folded and placed under the refrigerator
3. Coiled up and placed near the compressor
4. Integrated in the liner of the refrigerator
If the condenser isn't a big grid on the back of the refrigerator, it will
always have a cooling fan nearby to draw room air over the tubes and fins--to
dissipate the heat from the tubes and fins. The high-pressure refrigerant
gas, coming from the compressor, flows through the condenser and becomes a
liquid. As this occurs, the refrigerant gives off heat. The heat is conducted
away from the tubes by the fins.
Metering Device (Capillary Tube)
The metering device in most household refrigerators is a capillary tube, a tiny
copper tube. The capillary tube is attached from the end of the condenser to the
beginning of the evaporator. The capillary tube controls the pressure and flow
of the refrigerant as it enters the evaporator. Once the liquid
refrigerant has traveled the length of the condenser, it is forced through the
capillary tube.
Evaporator
The evaporator is always located on the inside of the refrigerator, usually
inside the freezer compartment. It also resembles a radiator. When the
liquid refrigerant comes out of the small capillary tube, it’s injected into the
larger tubes of the evaporator causing a pressure drop. This pressure drop
allows the refrigerant to expand back into a gaseous state. This change of state
from liquid to gas absorbs heat. The gaseous refrigerant travels through the
evaporator tubes, back out of the refrigerator and down to the compressor to
begin the circulation process again. Because the evaporator is absorbing
heat, it is very cold to the touch. The coldness causes any humidity in the air
to freeze on the evaporator as ice or frost. (See the Automatic defrost
section). The fan inside the freezer compartment circulates the air of both the
refrigerator and/or freezer to keep the temperature constant.
All refrigerators have a thermostat to maintain the proper temperature. These
are usually very simple devices. When the refrigerator reaches the set
temperature, the thermostat interrupts the electricity flow to the compressor,
which stops cooling.
Refrigerators with internal lighting normally have only one functional
component--the switch--which is usually a white push-button mounted inside the
refrigerator near the door. When the refrigerator door closes, the door pushes
the switch to turn the light off. When the door opens, the button automatically
pops back out to turn on the light. The light bulb itself is usually a standard
appliance bulb.
The ice maker is a small appliance within a freezer. It's usually independent
of the other systems of the refrigerator. Ice maker systems have two basic
functional components: the icemaker itself, and the water fill valve.
This is the most common ice maker operation cycle:
The ice maker sends a signal to the water fill valve (normally located on the
outside back of the refrigerator, near the bottom) to open and let water into
the ice maker tray. The amount of water is determined by a cam and switch within
the ice maker control panel. The icemaker sends the signal to open the water
valve for a certain length of time (7-10 seconds) then stops the signal. The ice
maker waits until the water is frozen--which it senses with a small thermostat
located near the water tray. When the tray reaches approximately 10-15 degrees
Fahrenheit , the ice maker begins to harvest (eject) the cubes. To harvest
the cubes, the ice maker first turns on a small heater beneath the tray. The
heater warms the tray slightly, which allows the ice cubes to move freely.
Then a sweep fork rotates and pushes the cubes up and out of the tray.
While the ice maker is dumping the cubes into a holding bin, a metal wire
similar to a coat hanger swings up to let the cubes drop below it. When the
cubes have dropped, the wire comes back down. If the holding bin is full of ice,
the wire cannot come all the way back down, which stops further production of
ice. When the wire is allowed to come back down all the way, the ice maker
refills with water and repeats the process.
Back to Top
There are several different systems for delivering ice and water through the
refrigerator door. What follows is an explanation of the common attributes of
all of the systems.
Ice dispenser
For a refrigerator to provide ice through the door, the ice maker first dumps
the ice it produces into a large bin. To request ice at the door, a person
presses a lever that activates a switch. The switch turns on a motor that
rotates the auger. When the auger rotates, it pushes ice out of the bin, through
a chute to the user.
Water dispenser
The water dispenser works much like the ice dispenser. To request water at the
door, a person presses a lever on the front of the refrigerator that activates a
switch. The switch turns on an electric water valve at the back of the
refrigerator. Water flows through the valve into a tube, then flows into a
container in the refrigerator to be chilled. As new water enters the container,
the water that is displaced flows through a separate tube to the user.
All refrigerator/freezer doors have a seal--a rubber-like gasket attached to
the door. Usually white, almond, black, or brown, the seal's job is to keep the
cool air inside the refrigerator and the room air out. The seal is lined
with a magnet that runs its length and width. The magnet helps to hold the door
closed and create a tight seal. The screws that hold the seal to the door also
hold the door liner in and help to "square" the door. The hinges allow the
door to swing open. Some hinges also assist the door in closing. For the door to
close properly, the hinges must be correctly adjusted.