• SkillCat Team

How Does Domestic Refrigerator Work: A Complete Guide - Part 2

Updated: Sep 9

Working of Domestic Refrigerators: Chapter 2


In this module, we will learn the defrost system used in the refrigerator. Skip to quiz!!


Defrost System


Recall that the temperature in the refrigerator's freezer section is close to 0°C (32°F) or lower. The moisture present in the air inside the room freezes when it comes in contact with the evaporator coil of the refrigerator. This will form a frost layer on the evaporator coil.


The thick layer of frost deposit on the evaporator coil restricts the flow of air passing over the evaporator coil. This will also reduce heat transfer between air and evaporator coil. The frost will not allow circulating air from the freezer to the fresh food section.


Defrosting is the process of removing the ice or frost from the evaporator or freezer. The image to the right shows defrosted evaporator coil and frosted evaporator coil.


Defrosting is an essential part of our refrigerator maintenance checklist, as frost adversely affects our cooling performance. There are several defrosting techniques. These include:

  • Manual defrost,

  • Semi-automatic defrost, and

  • Automatic defrost

Manual defrosting can be done by turning off the refrigerator. As we turn off the refrigerator, the refrigeration cycle stops. The cooling coil temperature rises to room temperature, thus allowing the frost to melt away.


In a semi-automatic defrost system, we need to push a button near the freezer to activate the defrosting function. This will turn off the compressor. The refrigerator will turn on automatically after defrosting is completed.


In the semi-automatic defrost system, the manufacturer sets the defrosting time. It is brand-specific and can vary for every refrigerator. When we defrost manually, the defrost time is set by us and requires more attention.


We need to defrost the refrigerator manually every three days. An automatic defrost system does not require human intervention. An automatic defrost system prevents the formation of frost by activating an internal heating system.


The heating system directs the heat to the cooling coil. This heat will melt the frost over the cooling coil. Defrost procedure is applied periodically by stopping the system. The time duration for which this is done is one defrost cycle.


Recall that a solenoid valve controls the flow of refrigerant depending on the electrical signals it gets. During the defrost cycle, a solenoid valve interrupts the refrigerant flow to the evaporator. This will ensure that the refrigerant in the evaporator does not get heated.


Then, the electrical heating elements are energized, and the evaporator fan blows hot air over the evaporator coil. This will melt the ice accumulated during the refrigeration cycle.


A defrost cycle occurs after every eight hours in an automatic defrost system. Most of the time, the refrigerator may not need to go into defrost every eight hours.


The time between two defrost cycles depends on several factors. These include:

  • How many times we have opened the doors, and

  • How long the compressor has run

Instead of turning on an energy-consuming heater every eight hours in modern refrigerators, we can use adaptive defrost control. Adaptive defrost control (ADC) is what makes refrigerators energy efficient. It varies the length of time it takes the machine to go into defrost.


An adaptive defrost control uses a control board to vary the time interval between defrost cycles. We will look into each control component of the defrost system in a later topic.


The adaptive defrost control (ADC) will continually adjust the defrost intervals based on the following:

  • Number of door openings,

  • Compressor run time, and

  • Time passed after the last defrost cycle

Recall that the moisture present in the air freezes when it comes in contact with the evaporator coil. Outside humid air enters the fridge every time the door is opened. This increases the frost load. The ADC will adjust the time between defrost cycle to match the change in the frost load.


ADC will function the same way by monitoring the last defrost cycle. For example, if the defrost cycle duration is longer, it indicates a light frost buildup. Then, the adaptive defrost control will increase the time for which the system and compressor run.


Similarly, if the defrost cycle duration is shorter, it indicates a heavier frost buildup. The adaptive defrost control will decrease compressor run time between the defrost cycles by two hours.



Drain Line


During defrost cycle, ice melts to form water. This water flows down through the interior walls at the back of the fridge. We use a tube to carry this water called a drain line. The water goes through a drain line to the bottom of the refrigerator cabinet.

The drain pan collects the water that flows out of the fridge. A drain pan is a water tray that collects and stores water. The water then evaporates into the air.


Defrosting is the process of removing the ice or frost from the evaporator or freezer. Defrosting techniques are:

  • Manual defrost,

  • Semi-automatic defrost, and

  • Automatic defrost

Adaptive defrost control (ADC) is what makes refrigerators energy efficient. A drain pan is a water tray that collects and stores water.


Additional Systems


In this module, we will learn additional systems used in the refrigerator. Skip to quiz!


Dispenser


When it comes to side-by-side and french door refrigerator models, they are equipped with a dispenser system. This dispenser system consists of:

  • Water dispenser, and

  • Ice maker.

The new and improved models have dispensers built in the door. The commonly offered features of refrigerator dispensers are:

  • Chilled water,

  • Crushed ice, and

  • Cubed ice

Let us discuss each of the dispenser systems in detail.


Water Dispenser


A water dispenser is a device for supplying chilled water. It provides us clean filtered drinking water.


The water supplied by the dispenser system is filtered using a water filter. A simple carbon filter treats the drinking water dispensed from a refrigerator. This stops chlorine, fluorine, and other harmful impurities into the water.


Because of the water dispenser, we do not need to fill in the water bottles and check their amount. We have to press the button to get cold water immediately.


The water for the dispenser system in a refrigerator is supplied by one of the following means:

  • Water supply line connected to the refrigerator, or

  • Manually filling the dispenser water tank.

Recall that a flexible hose can bend as needed. The dispenser is connected to the water supply system using a flexible hose.


Water Source The flexible hose connected to the building’s main water supply fills the reservoir automatically. If the connection to the water supply is not possible, then the water is poured into the tank manually.


A water dispenser makes cold water the same way a refrigerator makes its compartments cold. Recall that refrigerant boils off in the evaporator by absorbing heat from the refrigerator compartments. In the case of a dispenser, heat is absorbed from the water tank to get chilled water.


When we press the water dispenser lever in front of the refrigerator, it activates a switch in the refrigerator's door. The switch opens a valve in the back of the appliance. This will allow water to flow through the tubing into a water reservoir where it is dispensed.




Ice Maker


Recall that we use the freezer section to make ice cubes in the old refrigerators. We have to manually keep ice trays filled with water inside a freezer in these old systems. An icemaker automates the process of pouring water and extracting ice cubes from the ice tray.


Mechanical, electrical, and control components make ice-making automated. We will look at control and electrical components in a later topic.


The mechanical components that are present inside the ice maker unit are:

  • Ice tray,

  • Ice bucket auger, and

  • Ice crusher blade.

Let us learn about each of them.


The ice tray is also called as ice mold. The water from the supply line fills the mold of an ice tray every cycle. Once the water freezes control device turns on the heater to loosen the ice from the mold.


An auger is a metal shaft with a blade that scrapes or cuts the hard material. As the auger motor rotates, the ice bucket auger turns and lifts loosen ice from the ice tray. Ice cubes are then released and dumped into a storage container in the freezer.


Ice crusher blade is a blade for chopping ice. We use a rotating blade and a stationary blade for chopping the ice.


Ice crusher blades are located inside ice crusher housing. They are mounted on the auger shaft. As the auger motor begins to rotate, the ice gets trapped between these blades to crush the ice.


We can see that how the mechanical components work to automate the process. At the beginning of the cycle, an electrical signal is sent to a water valve to fill the ice mold with water. Then, the freezer starts freezing the water.


After the ice cubes have been created, a heating coil is activated to loosen them from the trays. The ice bucket auger then pushes them out of the trays. When we press the lever or button of the ice maker built in the door, we get ice cubes.


We also need crushed ice for making mojitos on a hot summer’s day. When we press the crush ice button on our refrigerator door, ice cubes are trapped between the two sets of blades. The blades chop the ice cubes to get crushed in seconds.


How to operate a dispenser to get chilled water and ice. The operation of this system is brand-specific, and it differs for each model.



Twin cooling system


Some modern refrigerators have two separate evaporator systems. It makes use of one closed system for cooling the refrigerator and another system for cooling the freezer. Such a system is known as a twin cooling or dual evaporator system.


Twin cooling systems use a single compressor that connects to two separate evaporator systems. Twin cooling lets the compressor cool only the section that needs cooling. If we rarely use the freezer, then it allows us to stop cooling or freezer. This makes the refrigerator more efficient.


The cool air does not travel through the same duct to reach the two compartments. This prevents odor from transferring from one compartment to another.


When it comes to side-by-side and french door refrigerator models, they are equipped with a dispenser system. The dispenser system consists of:

  • Water dispenser, and

  • Ice maker.

Twin cooling systems makes the refrigerator more efficient.


Electrical Systems


In this module, we will take a look at the electrical systems of the refrigerator. Skip to quiz!


Electrical


A refrigerator is an electrically powered home appliance. We generally use a single-phase power supply for domestic refrigerators.

Electrical components work together to run the refrigerator system efficiently. They are also used to make the process of defrosting and ice-making automated.


Some of the electrical components used in the refrigerator are:

  • Electric motors,

  • Heaters, and

  • Interior lighting

Let us learn about each of them in detail.


Motors


Recall that an electric motor is a part of the compressor that provides rotation by consuming electricity.


Apart from the compressor, the motors used in refrigerators are:

  • Condenser fan motor,

  • Evaporator fan motor,

  • Auger motor, and

  • Dispenser Door Motor

Let us learn about each of them in detail.

Recall that we use a fan to force air over the condenser coils. The motor used for running this fan is the condenser fan motor.


Recall that the evaporator fan forces air over the cool evaporator coils inside the refrigerator. Much like a condenser fan motor, we use a motor for running an evaporator fan.


The auger motor spins the ice bucket auger and pushes the ice through the dispenser tray. If the auger motor is burned out or defective, the ice won’t move forward and fall through the tray.


The dispenser door motor opens and closes the dispenser door to prevent cold air from escaping the freezer. If the dispenser door motor is defective, the dispenser door won’t open. As a result, the dispenser will not dispense ice.


Heater


Refrigerator mainly use two heaters for functioning of defrost system and ice maker. These include:

  • Defrost heater, and

  • Ice mold heater

Let us discuss each of them.

The defrost heater is used to melt accumulated frost off the evaporator coil surfaces.


Defrost heaters are commonly located beneath a refrigerator's evaporator coils.


Ice mold heater is used to heat the ice made by the ice maker. When the ice maker freezes the water in the mold, the thermostat signals the heater. The heater then activates to loosen the ice cubes from the mold.


Interior Lighting


We must have noticed lights illuminating as we open the refrigerator door. This light helps to locate the things inside the refrigerator when we open the door.

The refrigerator light is controlled by a door sensor that detects the closing and opening of a door. We will learn about controls in the later topics.


Electrical components work together to run the refrigerator system efficiently.


Some of the electrical components used in the refrigerators are:

  • Electric motors,

  • Heaters, and

  • Interior lighting.

Control Systems


In this module, we will take a look at the control systems of the refrigerator. Skip to quiz!


Controls


Along with electrical systems, we also use control systems in the refrigerator. Control systems automatically adjust the operation of the refrigerator.

In the refrigerator, control systems can be divided into

  • Process controls,

  • Safety controls,

  • Defrost controls, and

  • Flow controls.

Let us learn more about each type of control in detail.


Process Controls


The purpose of process control devices is to automate refrigerator operations. These include the following control devices:

  • Switches,

  • Thermostat, and

  • Sensors

When we press a lever on our refrigerator door, it activates a small switch in the refrigerator's door. This micro switch is a water dispenser switch.


Recall that the water valve is a type of solenoid valve. It remains shut and opens once it receives an electric signal.


When the water dispenser switch is pressed, it operates a water valve in the back of the appliance. This allows water to flow through the tubing into a water reservoir. That is why when we press the lever, water is dispensed through the refrigerator door.


The ice maker has an ON/OFF switch similar to a light or power switch. This power switch is used to control the operation of this ice maker. If the unit is powered off, the ice maker stops making ice.


A refrigerator thermostat is essentially the controlling component of a refrigerator cooling system. It tells us the inside temperature of the refrigerator. We can adjust the temperature inside the fridge using a thermostat.


The refrigerator thermostat is located inside the refrigerator. It has a knob that looks like a dial or, in more modern appliances, a digital display.

Once a user sets the desired temperature, the thermostat maintains that temperature by sensing internal fluctuations. It senses the fluctuations using a temperature sensor. Recall that a temperature sensor is placed inside or near the thermostat to detect the temperature.


When the refrigerator is adjusted to the designated temperature, the temperature sensor passes the signal to the thermostat. The thermostat then stops the flow of electricity to the compressor, effectively stopping it from cooling the appliance.


Ice makers have a thermostat located in the ice maker mold. Once the ice maker has reached a cold enough temperature of approximately 15℉, the temperature sensor sends signal to the thermostat.


The thermostat then send electrical signals to the heating coil. This will start the heater, and ice cubes are detached from the mold.


Recall that freezer is cooler than refrigerator. This is why we use different temperature sensor to monitor temperature in each section. We use temperature sensor to monitor temperature in the: Freezer,

  • Defrost system, and

  • Refrigerator

The temperature sensor located on the evaporator coil is known as defrost sensor. This sensor does two functions:

  • Starting the defrost cycle, and

  • Stopping the defrost heater

Recall that we use defrost heater to melt accumulated ice over the evaporator coil. The defrost sensor senses evaporator temperature and sends signal to the electronic control board. If the defrost sensor senses wrong temperature, the electronic control board wont turn on the heater.


Defrost sensor shuts off the defrost heater when the heat near the evaporator has reached a temperature required to melt the ice. If the defrost sensor fails, the heating element doesn't turn on, and there will be no defrosting.


We use a temperature sensor in the freezer to monitor the freezer temperature. Similarly, the refrigerator temperature is also monitored by using a temperature sensor.


Recall that we use lights to illuminate inside compartments of the refrigerator. The light is turned on or off automatically when we open or close the door. We use a door sensor to detect if the appliance door is open or closed.


A Hall effect sensor can be used to detect the door’s position. A Hall effect sensor is a type of sensor which detects the presence and magnitude of a magnetic field. This sensor is mounted to the frame of the appliance.


A permanent magnet actuator is mounted to the door. The sensor and magnet actuator is positioned in such a way that the sensor is activated when the door is closed, and the light will turn off. When the door is open, the magnet on the door is outside of the sensor’s activation range, so the sensor is deactivated and the light turns on.


Ice bucket level sensor is used to detect if the ice is filled to the top. It uses a mechanical arm over the ice bucket, which rises and falls with the ice level in the bucket. Once the ice reaches a certain level, a magnetic reed switch is activated.


The switch activates the level sensor, and the sensor converts the perceived data into an electric signal. When the ice bucket is filled, the sensor turns off the ice maker.


Defrost Controls

Recall that defrost cycle occurs after every eight hours in an automatic defrost system. The frequency of the defrost cycles and their duration are controlled by using defrost timer. The defrost timer also limits the maximum amount of time that the defrost heater can be energized.


Recall that adaptive defrost control (ADC) is what makes refrigerators energy efficient. This control system is operated using a control board.


Safety Controls


Safety controls prevent a hazard from occurring. Recall that safety control circuits are always in closed condition. If any abnormality happens, these will open and turn off the refrigerator system.