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Defrost System & Additional Systems


Working of Domestic Refrigerators: Chapter 3


Defrost System


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


Defrost Systems


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


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


Defrosting is the process of removing the ice or frost from an evaporator or freezer.


Defrosting is an essential part of our refrigerator maintenance checklist, as frost adversely affects 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 a refrigerator. As we turn off a refrigerator, the refrigeration cycle stops. The cooling coil temperature rises to room temperature, thus allowing the frost to melt away.


The manual defrost system is not used in modern refrigerators. This is because it becomes tiresome to defrost a refrigerator manually.


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. A refrigerator will turn on automatically after defrosting is completed.


In the semi-automatic defrost system, the manufacturer sets the defrosting time. It’s 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.


A heating system directs heat to the cooling coil. This heat will melt the frost on the cooling coil. This defrost procedure is applied periodically by stopping the system. The automatic defrost takes one defrost cycle to complete.


Recall that a solenoid valve controls the flow of refrigerant depending on the electrical signals it gets. During a defrost cycle, a solenoid valve interrupts the refrigerant flow to the evaporator. This will ensure that 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 melts the ice accumulated during the refrigeration cycle.


A defrost cycle occurs every eight hours in an automatic defrost system. Most of the time, a 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 a machine to start defrosting.


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


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 air freezes when it comes in contact with an evaporator coil. Outside humid air enters a fridge every time its door is opened. This increases the frost load. An ADC will adjust the time between defrost cycles to match the change in the frost load.


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


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



Drain Lines


During a defrost cycle, ice melts to form water. This water flows down through the interior walls at the back of a 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.


A drain pan collects the water that flows out of a 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 ice or frost from an 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 a refrigerator. Skip to quiz!


Dispensers


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 into the door. The commonly offered features of refrigerator dispensers are:

Let’s discuss each of these dispenser systems in detail.


Water Dispensers


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


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


Because of the water dispenser, we don’t need to fill water bottles or check their amount. We can press a button to get cold water immediately.


The water for a 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. A dispenser is connected to the water supply system using a flexible hose.


A flexible hose connected to a building’s main water supply fills the reservoir automatically. If a connection to the water supply is not possible, then 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 an evaporator by absorbing heat from 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 the front of a refrigerator, it activates a switch in the refrigerator's door. This switch opens a valve in the back of the appliance. This allows water to flow through tubing into a water reservoir where it’s dispensed.



Ice Makers


Recall that we use the freezer section to make ice cubes in older 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 an ice tray.


Mechanical, electrical, and control components make ice-making automated. We’ll look at control and electrical components in a later module


The mechanical components present inside an ice maker unit are:

  • Ice tray,

  • Ice bucket auger, and

  • Ice crusher blade.

Let’s learn about each of them.


Ice trays are also called ice molds. The water from a supply line fills the mold of an ice tray every cycle. Once the water freezes, a control device turns on a heater to loosen the ice from the mold.


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


Ice crusher blades are blades for chopping ice. We use a rotating blade and a stationary blade for chopping ice


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


We can see how the mechanical components work to automate this process. At the beginning of a 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 ice cubes have been created, a heating coil is activated to loosen them from their trays. The ice bucket auger then pushes them out of the trays. When we press the lever or button of a built-in ice maker, we get ice cubes.


We also need crushed ice to make mojitos on a hot summer day. When we press the crushed ice button on our refrigerator door, ice cubes are trapped between two sets of blades. These blades chop the ice cubes to be crushed in seconds.


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



Twin Cooling Systems


Some modern refrigerators have two separate evaporator systems. It makes use of one closed system to cool the refrigerator, and another system to cool 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 a compressor cool only the section that needs cooling. If we rarely use the freezer, then it allows us to stop cooling our freezer. This makes a refrigerator more efficient.


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 make a refrigerator more efficient.


 

Question #1: What does ‘defrosting’ a refrigerator mean?

  1. Removing ice from the evaporator coil

  2. Removing ice over the compressor

  3. Removing ice over the condenser coil

  4. Removing ice over the metering device

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Answer: Removing ice from the evaporator coil

Defrosting is the process of removing the ice or frost from an evaporator coil or freezer.


Question #2: A semi-automatic defrost system does not require human intervention.

  1. True

  2. False

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Answer: False

False. We need to push a button near the freezer to activate the defrosting function in a semi-automatic defrost system.


Question #3: What is a defrost cycle?

  1. Process of circulating cold air

  2. Time for circulating air

  3. Time duration for which defrost procedure is applied

  4. Process of making ice

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Answer: Time duration for which defrost procedure is applied

This defrost procedure is applied periodically by stopping the system. The automatic defrost takes one defrost cycle to complete.


Question #4: Which component is used to melt the ice in an automatic defrost system?

  1. Thermostat

  2. Condenser

  3. Fan

  4. Heater

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Answer: Heater

An automatic defrost system melts the ice by using a heater.


Question #5: Which system makes modern refrigerators more energy efficient?

  1. Water cooler

  2. Automatic defrost system

  3. Adaptive Defrost Control

  4. Automatic ice maker

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Answer: Adaptive Defrost Control

Adaptive defrost control (ADC) is what makes refrigerators energy efficient.


Question #6: How does an automatic defrost system continuously adjust the defrost intervals? (select all that apply)

  1. Monitoring the time passed since the last defrost cycle

  2. Monitoring the air temperature in a room

  3. Monitoring the temperature of the freezer

  4. Monitoring the number of door openings

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Answer: Monitoring the time passed since the last defrost cycle

Monitoring the number of door openings

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

  • Number of door openings,

  • Compressor run time, and

  • The time passed after the last defrost cycle.


Question #7: What is the function of a drain pan?

  1. To make ice

  2. To dispense water

  3. To collect water from a defrost system

  4. To filter water

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Answer: To collect water from a defrost system

A drain pan is a water tray that collects and stores water.


Question #8: What features are offered by a refrigerator's dispenser? (select all that apply)

  1. Chilled water

  2. Crushed ice

  3. Ice-cream

  4. Cubed ice

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Crushed ice

Cubed ice

The commonly offered features of refrigerator dispensers are:


Question #9: What is the water source for a dispenser system in a refrigerator?

  1. Water is not required in a dispenser

  2. Water supply line connected to the refrigerator

  3. Water made by melting ice

  4. Rain water

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Answer: Water supply line connected to the refrigerator

The water for a 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.


Question #10: Which of the following is a component used inside a refrigerator ice maker? (select all that apply)

  1. Ice bucket auger

  2. Compressor

  3. Crusher blade

  4. Condenser

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Answer: Ice bucket auger

Crusher blade

The mechanical components present inside an ice maker unit are:

  • Ice tray,

  • Ice bucket auger, and

  • Ice crusher blade.


Question #11: What is the purpose of the heating coil inside an ice maker?

  1. Loosen ice from its tray

  2. Melt ice in its tray

  3. Defrost ice over evaporator coil

  4. Make chilled water

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Answer: Loosen ice from its tray

After ice cubes have been created, a heating coil is activated to loosen them from their trays.


Question #12: A twin cooling system uses two separate compressors to make the refrigerator more efficient.

  1. False

  2. True

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Answer: False

False. Twin cooling systems use a single compressor that connects to two separate evaporator systems. This makes a refrigerator more efficient.


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