HOW
REFRIGERATORS WORK
 Refrigerators
have separate systems that are responsible for different features. However,
not all refrigerators have all systems. To look for information about the
operation of your refrigerator, click one of these topics:
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Automatic
defrost
Cooling
Temperature control
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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.
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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.
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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.
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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.
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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
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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.
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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:
- A large
black grid mounted to the back of the refrigerator
- Folded and
placed under the refrigerator
- Coiled up
and placed near the compressor
- 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Proper
installation of a refrigerator is both easy and important. The primary
concerns are that the unit has sufficient clearance from the walls for
proper ventilation, that it is not pinching any electrical cords or water
lines, and that it is level. Many refrigerators must be tilted back slightly
so that the doors self-close. Consult your owner's manual for further
installation instructions.
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