• SkillCat Team

Refrigeration Cycle Components

Updated: Apr 7

Refrigeration Theory: Chapter 3


In this module, we will go over the individual components of the refrigeration cycle. We will also discuss what happens to the refrigerant in each component and the function of each component. Skip to quiz!


1. Overview of Components


Aside from the refrigerant flowing through the system, the four key components of a refrigeration cycle are:

  1. Evaporator

  2. Compressor

  3. Condenser

  4. Metering Device— also known as a Thermal Expansion Valve (TXV)

Let’s now look at each of the components on their own, starting with the evaporator.



2. Evaporator


The evaporator is located inside the home. This is where the refrigerant absorbs heat from indoor air, changing from liquid to vapor.


As seen in this video, the evaporator coils provide more surface area for hot indoor air to pass over. This increased surface area allows more heat to be transferred to refrigerants inside the coils.


We also see in this schematic that as refrigerants in the evaporator coils absorb heat, it changes state from liquid to vapor. Refrigerant gets heated up past its boiling point, which makes it superheated vapor by the time it leaves the evaporator.


This change into a superheated vapor state is indicated in the color change of the coils from blue (liquid) to red and yellow (vapor). Vapor refrigerant is let out from the evaporator to the next component, the compressor.



3. Compressor


After the refrigerant is boiled to a vapor in the evaporator, it is sent through the suction line to the compressor. Since refrigerant comes out of the evaporator as a superheated vapor, it will enter the compressor as a superheated vapor.


The compressor’s job is to increase the pressure of the refrigerant. Recall that as pressure increases, temperature increases. This is exactly what the compressor does. We saw a visual representation of that in the previous video.


Refrigerant is then sent from the compressor to the next component, the condenser.



4. Condenser


The condenser is located outside the home so that coils containing the refrigerant can come into contact with outdoor air. The condenser’s job is to eject heat into the outside air.


Refrigerant is sent from the compressor to the condenser via the hot gas line since refrigerant exits the compressor as a hot, high pressure gas. As seen in the video, the condenser is housed in the same unit as the compressor.


Since the compressor increased the temperature of the refrigerant, the refrigerant is now hotter than the outside air. This causes heat to transfer from the refrigerant in the condenser coil to the outdoor air. When heat transfers away from the refrigerant, this cools the refrigerant.


In this video, we see blue arrows going into the unit. This represents cooler outdoor air flowing over the condenser coils. Recall that this does not mean outdoor air is “cool”. It just means that it is at a lower temperature than the compressed refrigerant inside the coils.


As the outdoor air passes over the condenser coils, it absorbs heat. Air that is exiting the unit is hotter because it has absorbed heat from the refrigerant in the coils. This is why the arrows leaving the unit are red.


Think of a steaming mug of coffee. Because it is hotter than the surrounding air, heat will transfer from the coffee to its surroundings. You can feel the heat transfer out when you wrap your hands around the mug. Recall that heat transfers from high heat to low heat. This is basically what happens in condenser coils.


Recall that as temperature decreases in a substance, it will condense, which is the process of changing from vapor to liquid. As discussed earlier, we see this commonly on windows on a cold day. Heat transfers from water vapor in the air to the cold windows, condensing the water vapor to liquid droplets.


In the condenser, heat transfers from the refrigerant to the outside air. The refrigerant inside the condenser cools until it changes state from vapor to liquid.


Refrigerant is then sent from the condenser to the next component, the metering device/ thermal expansion valve (TXV).



5. Metering Device


Refrigerant enters the metering device from the condenser via the liquid line, since refrigerant has cooled enough to completely change state to a liquid.


The metering device decreases the pressure of the refrigerant so that it can be sent back to the evaporator. There, it can repeat the cycle and continue absorbing heat from inside.



6. Conclusion


There are four main components to the refrigeration cycle: evaporator, compressor, condenser, and metering device/ thermal expansion valve (TXV). The main function of the refrigeration cycle is to absorb heat from indoor air and dispel it outdoors.



Question #1: When the refrigerant enters the evaporator, what state is it in?

  1. Solid

  2. Liquid

  3. Vapor

  4. Water


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Answer: Liquid

The refrigerant starts off as a liquid in the evaporator. Here, the refrigerant absorbs heat from the air to change state from liquid to vapor. This means that it starts off as a liquid.



Question #2:When the refrigerant exits the evaporator, what state is it in?

  1. Solid

  2. Liquid

  3. Vapor

  4. Water


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Answer: Vapor

In the evaporator, refrigerant absorbs heat from the indoor air to change state from liquid to vapor. This means that when the refrigerant leaves the evaporator, it is fully in the vapor state.



Question #3:After the evaporator, which component does the refrigerant go to next?

  1. Condenser

  2. Compressor

  3. Metering Device

  4. Your AC Unit


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Answer: Compressor

After the evaporator, refrigerant goes to the compressor.



Question #4: When the refrigerant enters the compressor, what state is it in?

  1. Supercooled vapor

  2. Supercooled liquid

  3. Superheated Vapor

  4. Superheated liquid


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Answer: Superheated Vapor

After the evaporator, all of the refrigerants has heated beyond its boiling point, making it a superheated vapor. This means that from the evaporator, entering into the compressor, the refrigerant is in the superheated vapor state.



Question #5: What is the compressor’s job?

  1. To cool the superheated vapor

  2. To increase the temperature

  3. To increase the pressure

  4. To decrease the temperature


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Answer: To increase the pressure

The job of the compressor is to increase the pressure of the refrigerant.



Question #6: The vapor leaving the compressor is lower in pressure than the vapor entering the compressor.

  1. True

  2. False


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Answer: False

The job of the compressor is to increase the pressure of the refrigerant. So the vapor refrigerant

leaving the compressor would be higher pressure than the vapor refrigerant entering it.



Question #7: Does the refrigerant change state in the compressor?

  1. Yes, it changes from a vapor to a liquid

  2. Yes, it changes from a liquid to a vapor

  3. Yes, it changes from a liquid to a solid

  4. No, it does not change state


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Answer: No, it does not change state

The refrigerant does not change the state in the compressor. It enters the compressor as a low pressure vapor and exits as a high pressure vapor. So, even though the pressure has increased, the state has not changed.



Question #8: What is the condenser’s job?

  1. To cool the high pressure vapor

  2. To heat the high pressure vapor

  3. To increase the pressure

  4. To decrease the pressure


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Answer: To cool the high pressure vapor

The job of the condenser is to decrease the temperature of the refrigerant by exposing it to outdoor air.



Question #9: In the condenser, the refrigerant changes state.

  1. True

  2. False


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Answer: True

True. In the condenser, the refrigerant cools by coming into contact with outdoor air. As it cools, it changes from a high pressure vapor to a high pressure liquid.



Question #10: The condenser is doing an opposite job of which component?

  1. Evaporator

  2. Compressor

  3. Metering Device

  4. Suction Line


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Answer: Evaporator

The condenser's job is to decrease the temperature of the refrigerant by exposing it to outdoor air. This is the opposite of the evaporator, which increases the temperature of the refrigerant because this cools the indoor air.



Question #11: What is the function of the metering device?

  1. To decrease pressure

  2. To increase pressure

  3. To decrease temperature

  4. To increase temperature


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Answer: To decrease pressure

The metering device’s job is to decrease pressure so that the refrigerant can be cycled back to the evaporator to absorb more heat from indoor air.

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