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:
Automatic defrost
Cooling
Temperature control
Lighting
Icemaker
Ice and water dispenser
Door seals and hinges
Installation
Automatic defrost
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.
Cooling
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:
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.
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.
Temperature control
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.
Lighting
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.
Ice maker
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.
Ice and water dispenser
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.
Door seals and hinges
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.
Installation
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.