Freezers have separate systems that are responsible for different features. Not all freezers have all the systems we discuss. To understand how your freezer works, look for information about the systems that apply to it:
Years ago, all freezers had to be defrosted manually. You would turn off the freezer, open the door(s), and allow any frost build-up to melt. When the frost had completely melted away, you would turn the freezer back on. You did this periodically.
Today, many freezers are self-defrosting. Self-defrosting means what it implies--though frost continues to accumulate inside the freezer, it melts automatically. The self-defrosting system has three functional components:
Continual - This timer is like a clock. It continually advances, 24 hours a day. Every 6 to 8 hours, the timer turns off the cooling system and turns on the defrost heater. After 20 to 30 minutes, the timer transfers power away from the defrost heater and back to the compressor.
Intermittent - This timer advances until a predetermined time interval of 6 to 8 hours. At the interval, it shuts off the compressor and turns on the defrost heater. When the defrost thermostat senses a specific rise in temperature--indicating that the frost on the evaporator has melted--it again sends power to the defrost timer, which then completes the cycle.
The defrost heater is an electric element 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 when the timer allows electricity to flow through it. Because the heater is 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 freezer. The water is then evaporated by either:
A fan that blows warm air from the compressor motor over the pan and out the front of the freezer
Or, if the pan is on top of the compressor, by the heat of the compressor.
The defrosting process ends after either the amount of time specified on the timer or when a separate thermostat near the cooling coils (the defrost thermostat) senses that the heat near the coils has reached a specific temperature.
You'll more quickly understand freezer cooling systems if you think of their action as "removing heat from the air in the freezer" rather than "cooling the air in the freezer." All residential freezers work on the same principle for cooling. They all have:
The compressor is the motor (or engine) of the cooling system. It's normally at the bottom of the freezer in the back. It's almost always black and about the size of a football. If the freezer is self-defrosting, the compressor may be behind a thin panel.
The compressor runs whenever the freezer 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.
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 freezer. On many freezers, it is integrated within the freezer cabinet and is completely out of sight. If the freezer is self-defrosting it may be:
A large black grid mounted to the back of the freezer
Folded and placed under the freezer
Coiled up and placed near the compressor
Integrated in the liner of the freezer
If the condenser isn't a big grid on the back of the freezer, 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.
The metering device in most household freezers 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.
The evaporator is always located on the inside of the freezer. It may be:
Integrated within the walls of the freezer, as in a chest freezer.
Integrated with the shelves of the freezer, as in an upright freezer.
Concealed behind a panel on the inside of the freezer.
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 freezer 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 to keep the temperature constant.
Freezers have a thermostat to maintain the proper temperature. These are usually very simple devices. When the freezer reaches the set temperature, the thermostat interrupts the electricity flow to the compressor, which stops cooling.
Freezer doors have a seal--a rubber-like gasket attached to the door. Usually colored white, almond, black, or brown, the seal's job is to keep the cool air inside the freezer and the outside 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 creates 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.
