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How air conditioners work diagram

How Air Conditioners Work - Archtoolbox

Air conditioning operates based on the principles of phase conversion, which is the transformation of a material from one state (or phase) of matter to another, such as when a material changes from a liquid to a gas. When a liquid to gas change occurs, the material absorbs heat. Conversely, when the material changes from gas to liquid, it releases heat. An air conditioner is basically a machine that forces phase conversion and uses the resulting heat transfer principles to cool buildings.

Air conditioners are comprised of many components, the primary ones being a fluid compressor, a condenser and an evaporator coil. We will pick a point in the air conditioning cycle and describe how the movement of the refrigerant through the system works to cool a building. Since the compressor is one of the most vital pieces of equipment in an air-conditioning system, let’s start there.

Air Conditioning Cycle

All air-conditioning systems utilize a specific material to undergo the phase conversion process. This material is called a refrigerant, and is contained within tubing which runs throughout the air-conditioning system. The refrigerant is pulled into the system’s compressor (item 1 in the diagram below) in the form of a warm vapor after leaving the evaporator coil (which will be explained further below).

The compressor increases the density of the incoming refrigerant vapor, causing it to increase in pressure and temperature. This is normally accomplished using a centrifugal system, where a series of spinning blades rapidly forces the vapor to the outside of the compressor chamber, at which point it exits. This hot, high-pressure vapor then travels to the air conditioner’s condenser (item 2) where it moves through a series of coils with thin metal fins attached. A fan blows air over the fins, and heat moves from the refrigerant to the fins and into the air stream, very similar to the method a radiator uses to remove heat from the coolant circulating within in a car engine. The air that is run over the condenser coils is vented to the building exterior and is released to the atmosphere.

This trip through the condenser causes the vapor to lose a significant amount of heat and it subsequently changes phase from a gas to a high temperature liquid. The liquid refrigerant is then forced through an expansion valve (item 3) which is basically a pinhole that causes the liquid to form a mist. A sudden pressure drop and material expansion when the liquid turns into a mist results in a rapid cooling of the fluid as it throws off heat energy. This cold mist travels through the evaporator coil (item 4) which is located directly in the air stream of a circulation fan which pulls air from within the building. The fan pushes the air across the cold coils, which pulls heat from the air, causing the air to cool. The transfer of heat to the refrigerant causes it to change back into a warm vapor and it enters the compressor to begin the cycle again.

Diagram of How Air Conditioners Work

Moisture Removal - Dehumidification

In addition to cooling internal spaces, air-conditioners also provide dehumidification. The original intent behind the invention of the air conditioner was to remove humidity from industrial spaces, with the cooling of the air considered a secondary effect. The removal of moisture during air-conditioning unit operation occurs when the relatively warm air of the building interior is pulled across the cold evaporator coils. Since physics dictates that warm air can hold more water than cool air, the cooling of the building air as it contacts the evaporator coils causes it to release moisture which forms as condensation on the coils. This condensation eventually drips off and is collected and drained off to the building exterior or to a sewer connection. A reduction in building humidity tends to improve the comfort level of the occupants by enhancing the effectiveness of the body’s natural cooling system. The combination of humidity removal and temperature decrease defines the “conditioning” of the air.


Air-conditioning refrigerants typically consist of materials that are noncorrosive and have the ability to easily transition between gas and liquid phases at the operating temperatures of the air-conditioning system. Commonly used refrigerants are carbon dioxide, ammonia and chemicals called non-halogenated hydrocarbons, with the type of refrigerant selected based on the specific cooling application.

In the past, chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) were used, but CFCs were phased out of production in the 1990s and HCFCs will be phased out of production by 2030 because of their ozone depletion potential.

Article Updated: May 29, 2021

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Air Conditioner Working Principle Simple Explanation with Diagram

After spending countless hours studying how an air conditioner works, I put together all my research and explaining them in layman's terms here.

To produce this article, I read books and journals to boil things down and organize the technical terms into simple language for easy understanding.

In this article, I'll be covering more than just the refrigeration cycle. I'll be explaining the relevant processes and components to give you the whole picture of how an air conditioner works. This will be quite long so let's get started.

If you prefer video, I have one on YouTube which go in-depth into the fundamental of how air conditioners work. Below is the video about how air conditioners work:

Basic Working Principle of An Air Conditioner

The principle of air conditioning is based on the laws of thermodynamics. An air conditioner operates using the refrigeration cycle. Specific refrigerants are needed as the working fluid in the refrigeration cycle.

An air conditioner goes through 4 processes; compression, condensation, expansion, and evaporation. Typically, an air conditioner is made up of 4 major components; compressor, heat exchanger, fan, and expansion valve.

AC Working Principle in Diagram AC Working Principle with Components

Besides, air conditioners have other components such as filter drier and printed circuit board, these components will be covered later in this article.

In an air conditioning system, pipes are needed to transfer heat energy from indoor to outdoor. Insulation is always required in an air conditioning system to prevent energy loss.

An air conditioner not just cools or reduces the temperature of the air, it also dehumidifies the air to a level that is comfortable to humans.

An air conditioner also provides a certain degree of air filtration during the cooling process.

Refrigerant for Air Conditioning

Refrigerant is the working fluid in an air conditioning system. Refrigerant is a general name given to a group of chemicals such as hydrofluorocarbons (HFCs), ammonia, propane, and carbon dioxide.

The fluid used in the refrigeration cycle is called a refrigerant, makes sense. A refrigerant doesn't necessarily have to be a chemical that we rarely heard, even air and water can be called a refrigerant as long as they are the working fluid in the refrigeration cycle.

A picture of R32 or HFC-32 refrigerant contained in a tank.

Among the refrigerants, hydrofluorocarbon or HFC is best suited for air conditioners. HFC is a family name for its members. Some of the HFC members are familiar names such as R132a, R410A, and R32.

HFC is the most common type of refrigerant used in residential air conditioners, particularly R410A and the newer one, R32. Check out my post on why R32 is the best refrigerant for air conditioners.

Older air conditioners mostly used R22 refrigerants. R22 falls under the family name called chlorofluorocarbon or CFC. Most CFCs, including R22, are getting banned in most countries due to their ozone-depleting capability that contributes to global warming.

Eventually, R22 and other CFCs will be phased out and newer, more environmental-friendly refrigerants will be replacing them.

Why Refrigerant is Used in Air Conditioning Systems?

Refrigerant is used in an air conditioning system to transfer heat energy. A refrigerant absorbs heat from a room and rejects it outside the house. Thus, cooling the room.

R22, R410A, and R32 are the common refrigerant used in residential air conditioners because of their unique chemical properties. Below are some of the desirable characteristic of a refrigerant:

  • Low boiling and freezing point
  • Chemical stability
  • Non-flammable
  • Low toxicity
  • Low cost
  • Environmental-friendly

To explain why a specific refrigerant must be used, let's assume if water is used as the refrigerant in an air conditioner. Water will not turn into vapor when it absorbed the heat from a room because of its high boiling point (relatively high when compared to R410A).

Subsequently, the liquid water enters into the compressor and the system fails because liquid cannot be compressed. Therefore, water can't be used as the refrigerant in an air conditioner.

On the other hand, if R410A is used as the refrigerant in an air conditioner, R410A will turn into gas form when it absorbed the heat from a room due to its low boiling point (about 5°C at 120 psi). Thus, the refrigerant gas can be compressed and the system works.

PT Chart of Refrigerant

A PT or pressure-temperature chart is an essential tool in a form of a table or chart, representing the relationship of pressure and temperature of a refrigerant to design and troubleshoot air conditioning systems.

I'll use R410A as the refrigerant to explain the PT chart and the operating pressure of an air conditioner.

A typical R410A split air conditioner operates at a pressure of about 120 psi at the suction line and about 430 psi at the discharge line. The operating pressure varies depending on the weather and heat load inside a room.

Simplified R410A Operating Condition

The pipe running from the condenser (outdoor unit) to the evaporator (indoor unit) is often called the liquid pipe because the refrigerant is in liquid form when traveling inside the pipe. The pipe running from the evaporator (indoor unit) back to the condenser (outdoor unit) is often called the gas pipe.

When discussing the refrigerant pressure, the gas pipe often breakdown into the suction line and discharge line, referencing from the compressor sucking and discharging the refrigerant.

A refrigerant has a fixed temperature at a given pressure. Increasing the pressure of a refrigerant will result in changes in its temperature. The relationship of pressure and temperature for R410A is shown in the below PT chart.

Using the PT chart, we can determine if the pressure of the refrigerant in an air conditioner is within the appropriate range or not. Incorrect pressure will cause problems such as not enough cooling and coil freezing.

Thermodynamics of Air Conditioning

Air conditioning process obeys the first law and the second law of thermodynamics. For simplicity, you can view the first law and second law of thermodynamics as the law of conservation of energy and thermal equilibrium respectively.

The law of conversation of energy states that energy cannot be created or destroyed, it can only be transferred. An air conditioner transfers heat energy from a room to the outside of a house, thus cooling the room. It does not create any “cold energy” to cool the room.

Thermal equilibrium is an instance where there is no net flow of thermal energy between two connected physical systems.

According to the second law of thermodynamics, two connected physical systems always arrive at a state of thermal equilibrium where the thermal energy always flows from the higher entropy system to the lower entropy system (can view as the thermal energy always flow from the hotter one to the colder one).

From the above illustration, the coffee will always become colder. The coffee will never absorb the heat from the ambient and become hotter because it will violate the second law of thermodynamics.

Cold refrigerant arrives at the indoor unit of an air conditioner. The heat energy from a room always absorbed by the cold refrigerant and carry away from the room. Thus, cooling the room.

Refrigeration Cycle Explained with Diagram

An air conditioner operates using the refrigeration cycle. There are many types of refrigeration cycles. The air conditioner is using the vapor-compression refrigeration cycle.

A simplified P-H diagram for actual vapor-compression refrigeration cycle.

The refrigeration cycle of an air conditioner can be illustrated by a P-H diagram. The y-axis represents the pressure and the x-axis represents the enthalpy. For enthalpy, you can think of it as energy.

4 Cycles of Refrigeration

Whenever an air conditioner is turned on, the refrigerant goes through these 4 stages: compression, condensation, expansion, and evaporation. The cycle keeps on until the air conditioner is turned off.

1. Compression

In this stage, external power is injected into the system to compress the refrigerant. The refrigerant must be in gas form in order to make the compression possible.

  • Pressure – increase
  • Temperature – increase
  • State – gas

During compression, the pressure and the temperature of the refrigerant gas increase, in preparation for the next stage.

2. Condensation

Condensation is a process where gas turns into liquid. Similarly, the compressed refrigerant, which is in gas form, turns into liquid form during this stage.

  • Pressure – no change
  • Temperature – no change
  • State – from gas to liquid

During condensation, heat is extracted from the refrigerant gas, the enthalpy or the energy of the refrigerant gas drops, no change in pressure. Also, no change in the temperature of the refrigerant because the energy is used to convert gas into a liquid.

3. Expansion

When the refrigerant reaches this stage, it is in liquid form. Although the pressure is reduced during condensation, it is still relatively high.

  • Pressure – decrease
  • Temperature – decrease
  • State – liquid & gas

During this stage, the liquid refrigerant expands rapidly causing a huge drop in pressure and temperature. After the expansion, the temperature of the refrigerant is about 5°C, ready to cool the room.

4. Evaporation

Evaporation is a process where the liquid turns back into gas. Now, the expanded liquid refrigerant begins the evaporation process by absorbing the heat from the room.

  • Pressure – no change
  • Temperature – no change
  • State – from liquid to gas

While absorbing the heat from the room, the liquid refrigerant gains energy and started to boil. Remember earlier I mentioned that the refrigerant has to have a low boiling point?

After the evaporation stage, all liquid refrigerant should turn into gas form, goes back to the compression stage, and the cycle continues.

8 Components of Air Conditioner

In this section, I'll introduce the 4 major components inside an air conditioner that perform the 4 processes mentioned earlier.

1. Compressor

The compression process is performed by the compressor of an air conditioner. The compressor is located at the outdoor unit of an air conditioner.

Scroll compressor on the left, reciprocating compressor on the right

The compressor of an air conditioner is like the heart of a human. It is the main engine that drives an air conditioner. Its compression power is what pushes the refrigerant to circulate between the indoor unit and the outdoor unit of an air conditioner.

Compressor consumes the most power among the components of an air conditioner and it is the single most expensive component to replace.

There are many types of compressors such as scroll, reciprocating, screw, and centrifugal. Most of the residential air conditioners such as the split unit are using a scroll compressor.

Basic operation of a scroll compressor by Aire Acondicionado.

A scroll compressor spins to perform the compression. Refrigerant gas enters the compressor at the outer ring and then, is forced to travel to the inner ring, squeezed and compressed in the process.

Compressor contributes the most noise and vibration in an air conditioner. Thus, compressor rubbers are needed to reduce the vibration. The rubbers are placed at the leg of a compressor.

Compressor rubbersA compressor shouting out of dissatisfaction

2. Condenser and Evaporator Coil

Condenser and evaporator coils are responsible for the condensation and evaporation process. The condenser coil is located at the outdoor unit while the evaporator coil is located at the indoor unit of an air conditioner.

Condenser coil at the left, evaporator coil at the right

The coils are where the heat transfer process happens in an air conditioner. In engineering terms, these coils are called heat exchangers. To be precise, they are called finned-tube heat exchangers.

A finned-tube heat exchanger is made of copper tubes and aluminum fins. Copper tubes are for the refrigerant to flow through while aluminum fins enhance the heat transfer process.

Illustration of processes happen at the condenser coil.

The material used for a heat exchanger is copper and aluminum because high-efficiency heat transfer is required. In another word, copper and aluminum are very good at conducting heat. This gives an air conditioner high energy efficiency and consumes lesser electricity.

Aluminum is silver in color in nature. Some air conditioners are equipped with blue color fins is because an anti-corrosion coating is applied to the aluminum fins to increase their durability.

3. Fan

Fans are used in air conditioners to circulate air through the condenser and evaporator coil. There are two sets of fans in a split air conditioner, one at the indoor unit and one at the outdoor unit.

The fans are designed to provide a certain airflow rate. For instance, a 1HP (horsepower) air conditioner will always have an airflow rate of about 350 cfm (cubic feet per minute).

A fan can break down into two parts: fan motor and fan blade. Fan motor consumes electricity and performs the spinning motion. The fan blade is usually made of plastic that is designed at a certain angle of attack so that it can push air effectively. When attached together, they blow air.

Too much airflow causes incomplete condensation and evaporation, affecting the performance and lifespan of the air conditioner. Excessive airflow at the evaporator coil slows down the dehumidification process, resulting in the relative humidity of air not reduced to a comfortable level.

Indoor Unit FanOutdoor Unit Fan

Fan blades are usually made of plastic due to their low cost and lightweight. The lesser it weight, the lesser energy it consumes. However, some applications required stainless steel which is a much more heavy material in order to resist corrosion.

The fan of an air conditioner consumes relatively less power, second to the compressor. Misaligned fans can produce excessive vibration and noise.

4. Expansion Valve

Expansion valve is a metering device that used to control the amount of refrigerant released to the evaporator while expanding it in the process causing a rapid drop in the pressure and temperature of the refrigerant.

An expansion valve can be found at the evaporator or the indoor unit of an air conditioner.

Thermal expansion valve on the left, electronic expansion valve at the right

Commonly, there are two types of expansion valves: thermal expansion valves and electronic expansion valves. The thermal expansion valve is also known as TXV while the electronic expansion valve can be called EXV or EEV.

A thermal expansion valve contains a small amount of expandable gas in its sensing bulb. When a certain temperature is reached, the gas expanded and triggers an opening of the valve, allowing a certain amount of refrigerant to pass through.

An electronic expansion valve relies on an electrical signal to control its valve opening.

Unlike a thermal expansion valve which has a fixed range of operation, an electronic expansion valve is more flexible on the range of operation because the strength of its electrical signals can be altered by reprogramming the controller.

See below for detailed video on how the thermal expansion valve works.

Modern air conditioners use electronic expansion valves to achieve a more precise refrigerant control. Over time, the electronic expansion valve can save more energy than the thermal expansion valve.

5. Filter Drier

Filter drier is a filtration device used to capture small dirt particles and remove excess moisture in a refrigeration system. Filter drier can be found inside the outdoor unit of an air conditioner.

A filter drier before and after cutting open

Particles such as metal chips and specks of dirt can be gathered inside refrigerant copper pipes during installation. When an air conditioner is turned on for the first time, these particles will be captured by the filter drier.

Besides, a filter drier removes excessive moisture in the refrigerant for the air conditioner to maintain its intended performance.

Because the refrigerant is circulating in a closed-loop, a filter drier only works whenever there is charging of refrigerant. In another word, excluding the initial startup, a filter drier is in action whenever there is a repair of refrigerant gas leakage.

The filter media inside a filter drier can't be replaced, one whole piece of the filter drier has to be changed. Hence, some technicians might recommend changing the filter drier when repairing a refrigerant gas leakage.

6. Printed Circuit Board

Printed circuit board or PCB or IC board or control board, is an electronic board in an air conditioner used to control the operation of almost all of the components including the compressor, fans, expansion valve, and others such as remote control and inverter.

PCB of an AC outdoor unit.

The PCB can be found in both the indoor unit and the outdoor unit of a split air conditioner. The indoor unit PCB allows the air conditioner to be remotely turned on/off, set temperature, fan speed, and timer.

The outdoor unit PCB provides on/off or inverter control to the compressor, regulates the condenser fan speed, and triggers safety devices in case of an emergency.

Modern air conditioners use PCB or electronic board extensively to provide better features such as mobile phone control via an app over the WiFi.

7. Accumulator Tank

Typically, you'll see three black tank-alike components inside an AC outdoor unit. They are different in sizes; small, big, bigger. They are the filter drier, compressor, and accumulator tank.

Accumulator tank is a protective device that prevents the liquid refrigerant from entering into a compressor, preventing the cause of irreversible damages to a compressor.

An accumulator tank is structured in a way that the gas refrigerant is prioritized over the liquid refrigerant when leaving the accumulator tank. Thus, protecting the compressor because liquid refrigerant is unable to be compressed.

AC refrigerant flow in a dissected AC accumulator tank.

I captured some of the images from AC Service Tech. Feel free to follow the link to an explanation video where they go in-depth on the accumulator tank.

8. Air Filter

Filter is used in an air conditioner to block dust and thus, simplify the cleaning process, maintain efficiency and prolong the lifespan of an air conditioner.

Fundamentally, a filter is not required for the operation of an air conditioner.

However, without a filter, dust will quickly gather at the condenser and evaporator coil, blocking air from passing through the coils, causing incomplete condensation and evaporation, affecting the performance and reducing the lifespan of an air conditioner.

With a filter, the majority of the dust can be captured before entering the coils. Once the filter gathered a significant amount of dust, it can be washed and reuse. A filter is an extremely convenient and cost-effective solution to maintain the performance of an air conditioner.

Split AC FilterFCU FilterBag FilterHEPA Filter

However, not all filters are washable. Usually, high-efficiency filters such as bag and HEPA filters, are not washable. They need to be replaced periodically to maintain their filtrating performance. These high-efficiency filters can be found in air conditioners in hospitals and clean rooms for semi-conductor.

Copper Pipe and Insulation for Air Conditioner

Copper pipes are used to connect the indoor unit and the outdoor unit of an air conditioner. Refrigerant circulates between the indoor and outdoor unit to remove heat from a room via the copper pipes.

Refrigerant pipes at the AC outdoor unit.

The refrigerant inside the copper pipe is very low in temperature when traveling from the condenser to the evaporator.

Thus, insulating the copper pipes is necessary to prevent the losses of energy (or the losses of the coldness) and hence, to prevent the drop of energy-efficiency of the air conditioner.

Besides, insulating the copper pipe prevents water droplets from forming around the copper pipes due to condensation. Therefore, preventing water dripping.

Air conditioning copper pipe and insulation

Copper pipe is always used to connect the indoor and outdoor unit of an air conditioner. No other materials are more suitable than copper. I wrote an article specifically on why copper pipes are used in air conditioning. The article covered the strength of copper in air conditioning and outlined why other materials are not suitable.

Dehumidification in Air Conditioning

An air conditioner not just cools the air but it also dehumidify or remove the moisture of the air.

Humans typically feel comfortable at temperatures around 22 °C to 27 °C and relative humidity at around 40% to 60%. Hence, an air conditioner must remove some of the moisture in the air to provide maximum comfort.

An air conditioner removes moisture through the condensation of water vapor in the air.

Not to confuse with the condensation of refrigerant, the condensation of air occurs at the evaporator or indoor unit of the air conditioner. During condensation, moisture in the air will form water droplets and discharged via the drain pipe of an air conditioner.

In order for the water vapor in the air to condensate, the temperature of the contacting surface must be below the dew point of the air at the given moment.

Air circulates back to the indoor unit of the air conditioner and passes through the chilling evaporator coil. Because the cold refrigerant is passing through the evaporator coil, the evaporator coil can be at a temperature below 10°C.

In Malaysia, the average dew point of air is 24°C. The temperature of the contacting surface (evaporator coil) is well below the dew point. Therefore, water vapor in the air condenses into liquid water and the relative humidity of the air drops, the air is dehumidified.

If you wish to know more, here are some of my other posts related to dehumidification:

  • Do mini splits dehumidify?
  • It is possible for air conditioners to make the air too dry?

Air Conditioner Wiring

Typically, a single-phase power cable connects to the outdoor unit of a residential split air conditioner. From the outdoor unit, one set of single-phase power cables is connected to its indoor unit. For inverter type, one extra signal cable is required for the indoor unit.

Most residential air conditioners are with a capacity of not more than 2.5HP. The rated current of a 2.5HP air conditioner is about 8A to 9A depending on brand and model. Thus, 3x1c 2.5mm2 PVC cable is sufficient. As for signal cable, it is usually 1x1c 1.5mm2 PVC cable.

Relevant post: Air Conditioner Wire Sizing Guide: Chart & Calculation.

Cables must be protected with conduit to prevent the cable “skin” or cable jacket from damages and causing cable short circuit and more serious issues such as electrocute.


First of all, at its core, an air conditioner is working based on the laws of thermodynamics. An air conditioner uses the refrigeration cycle to perform heat absorption and rejection and therefore, provide cooling.

Next, air conditioners require specific refrigerants to operate. The refrigerant in an air conditioner goes through 4 processes which are compression, condensation, expansion, and evaporation.

Then, there are 4 major components in an air conditioner: compressor, condenser & evaporator coil, fan and expansion valve are responsible for the 4 processes in the refrigeration cycle. Other components in the air conditioner are minor but important to the overall performance of the air conditioner.

Besides, copper is always used as the refrigerant pipe to connect the condenser (outdoor unit) and the evaporator (indoor unit), and aluminum are often used as the fin of the condenser & evaporator coil because both of them are very good heat conductor.

Moreover, an air conditioner not just cools the air but also dehumidifies the air to a level that is comfortable for humans. Water vapor condensates into liquid water and discharged through the drain pipe of an air conditioner, reducing the relative humidity of the air.

Lastly, air conditioners require power and thus, properly sized cables must connect the condenser (outdoor unit) and evaporator (indoor unit) with appropriate conduit for cable protection.

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The principle of operation of the air conditioner: device and scheme

Continental climate prevails in Russia. This means that in winter in all regions it is cool and snowy, and in summer it is hot. Because of this, people have a need to buy an air conditioner or split system. But how does the average person choose when stores offer dozens of options that differ in appearance, power and cost? To do this, it is necessary not only to understand the brands, but also to know the principle of operation of the devices.

How the air conditioner works

The system works on the principle of a closed cycle. The air in the room is cooled by passing through the heat exchanger of the indoor unit, where the refrigerant evaporates. Consider the scheme of operation of the device in stages.

  • The compressor installed in the outdoor unit compresses the refrigerant and in the gaseous state from the evaporator of the indoor unit pumps it into the condenser.
  • In the condenser, freon is cooled by heat exchange with outside air and condenses. All this happens in the heat exchanger of the outdoor unit.
  • Next, the refrigerant passes through the throttling device, where there is a sharp decrease in pressure and temperature of freon. In this case, part of the liquid refrigerant inevitably passes into the gaseous state.
  • Cold freon enters the heat exchanger of the indoor unit (evaporator), where, due to heat exchange with air from the room, it boils and passes from a liquid state to a gaseous state. The air, in turn, is cooled and enters the room.

Due to the operation of the air conditioner, water drops form on the evaporator - condensate. Usually, when installing the system, a separate tube is installed to drain the condensate. It goes outside or into the sewer so that there is no excess moisture in the room.

The direction of the outgoing air from the indoor unit is regulated by a special curtain and louvers horizontally and vertically.

How the inverter air conditioner works

The peculiarity of this device is that the compressor turns on once during the entire operation of the air conditioner and is constantly in this state, changing the number of revolutions depending on the load on the air conditioner. In turn, a conventional air conditioner (on / off) periodically turns on and off without changing the speed. The inverter saves energy and prolongs the life of the compressor, because it works without switching on / off, but smoothly changing the number of revolutions.

An inverter model will be more economical than any other air conditioner if it runs for at least a few hours without shutting down.

The inverter model, like a conventional air conditioner, has two units - external and internal. The outdoor unit has a compressor, copper freon pipes, a fan and a condenser. The internal block consists of the evaporator, the fan, blinds, the filter and the special pallet for the formed condensate.

Design and principle of operation of a split system

The usual classic split system consists of two modules (blocks) - external and internal. The device of the external block of a split system of the on / off type is almost always the same.

Outdoor unit

The outdoor unit includes compressor, condenser, four-way valve and capillary tube. All units have a filter-drier that cleans and dries the refrigerant from possible moisture ingress into the system and various kinds of contaminants. In inverter-type split systems, the control board is also located in the external unit, which is also found in multi-split systems. Due to the fact that the compressor is located in the outdoor unit, the noise level from the air conditioner in the apartment is much lower than from the street.

Dimensions of the outdoor unit may vary depending on the performance of the model as well as the brand.

The connection between the indoor unit and the outdoor unit is carried out with the help of freon pipelines. There is also a drainage line, and an electric cable for powering the indoor and outdoor unit.

The outdoor unit of the air conditioner must always be located on the street side. It is attached to the outside of the wall. If the air conditioner needs to be installed at a sufficient height from the ground and it is not possible to mount the outdoor unit in the usual way, climbers with special equipment and equipment are invited. Without such devices, it is impossible to install the outdoor unit high.

Also, the outdoor unit can be installed on the roof of buildings, on unglazed balconies and loggias, open common balconies or flights of stairs with open access to the street.

Outdoor units are often supplied in an anti-vandal case, if it is not provided by the manufacturer, then the unit installed at the level of the first floors can be additionally placed in a special protective box made of metal rods. In order to avoid the accumulation of snow or rainwater, as well as debris, a special sloping canopy is sometimes installed above the external blocks.

Indoor unit

The indoor units of a split system differ significantly from each other. Firstly, it depends on the manufacturer, i.e. all indoor units differ in design, secondly, the units differ in the type of installation, and, accordingly, they have a significant difference not only in the design of the front panel, but also in the case as a whole. Also, indoor units, depending on the manufacturer, power and model, may differ in components, functionality, overall dimensions.

Split system indoor units can be of the following types:

  • wall - they are designed to be mounted on the wall;
  • cassette - placed in the area of ​​the subceiling space;
  • channel - installed in the area of ​​​​the sub-ceiling space with a duct system;
  • floor-ceiling - can be installed both on the floor and in the area under the ceiling;
  • columned - installed on the floor, they are large in comparison with other types of indoor units of classic split systems.

The operation of the indoor unit is controlled by an electronic board. In the indoor unit there are filters for air purification, automation, an evaporator and a fan for blowing the evaporator heat exchanger.

The main functions of modern split-systems are ventilation, dehumidification, cooling, heating and maintaining the desired air temperature in the room.

Remote control. Almost all modern models of split systems are equipped with a remote control. With its help, not only turning the device on and off, but also managing all functions - setting the temperature, turning on the timer, programming tasks, turning on all the modes provided for by a particular model of air conditioner.

If the “I feel” function is implemented in the model, then thanks to the temperature sensor in the remote control, the air conditioner monitors the ambient air temperature in the room, and when the temperature set by the user is reached, the equipment maintains it.

The indoor unit adjusts the airflow direction by changing the louver angle.

The operation of the compressor of the outdoor unit is controlled by constant monitoring of all systems.

Features of floor standing units

These models are rarely used if a standard split cannot be installed. Floor air conditioners are also only stationary. Stationary models have the same principle of operation as a conventional air conditioner, except for the installation of an indoor unit. It is not placed under the ceiling, but at a height of half a meter from the floor. The outdoor unit is located on the street. Such split systems belong to the semi-industrial series. As a rule, they are more productive than household models.

Features of mobile models

Mobile model has only one unit, located indoors. It contains the compressor, evaporator and condenser. The mechanism of functioning is based on the processing of air that is inside the room.

It is usually not recommended to choose a mobile model, since the noisiest part will not be installed outside the window, but indoors. When the air conditioner is on, it will be uncomfortable for you to be in the room. In addition, they differ in low power.

What is the difference between an air conditioner and a split system? The air conditioner can not only cool the air, but also heat it, if provided by the manufacturer. Air conditioning is a general concept of climatic refrigeration. There are many types of air conditioners available today. An air conditioner can be called both a household appliance for air cooling, such as a window air conditioner or a mobile air conditioner, as well as a chiller - industrial climatic equipment of high power. For a more precise definition, there are names of air conditioners, for example, a split system.

Split system is an air conditioner consisting of two units - external and internal. The indoor unit includes a control system - automation, filters for air purification, a fan for blowing the evaporator heat exchanger and the evaporator itself. The outdoor unit includes a compressor, a condenser, a four-way valve, a capillary tube and an automation system.

A household split system is most often installed in relatively small areas, for example, a household wall split system is designed to create an optimal microclimate in rooms from 10 to 70 m2, depending on the power of the equipment. Therefore, such split systems are most often installed in apartments or small office premises.

One indoor unit is able to maintain the temperature in one room, if you need to maintain the temperature in several rooms at once, then there are multi-split systems for this. Such a system involves connecting several indoor units to one outdoor unit at once.

There are also other types of split systems that are more suitable for spacious large areas - shopping centers, restaurants, business centers, etc. All these split systems also have one internal and one external unit, they differ only in internal units and performance. Indoor units are divided according to the type of installation - cassette, channel, column, floor-ceiling, column.

Split systems may differ in options and functions, it depends on the model and manufacturer. For example, split systems may have a different number of cleaning air filters. The number of modes may also differ - some air conditioners have the following popular modes - “I feel”, night mode, self-cleaning, auto-restart, auto-shutdown, self-diagnosis, turbo mode, intelligent defrost, etc.

How to choose a split system for your home

When choosing an air conditioner for home use, consider the size of the room. For a small room (up to 15-20 meters), a 7000 BTU system is suitable. For rooms up to 25 square meters, it is better to choose a more powerful model - 9000 btu.

Think about the cost of electricity and choose energy-saving models A++, consumption of about 700-800 watts. If the budget allows, you can buy an A+++ air conditioner with a consumption of 500-600 watts.

Estimate the noise level. If possible, listen to how the system works, because you will have to be in the room while the air conditioner is running. Permissible noise value for the indoor unit - 19-32 dB.

Advantages and disadvantages of air conditioners

If you are going to buy an air conditioner or split system, you will be interested to know about the pros and cons.


  • Comfortable room temperature. Regardless of the weather outside, the split system will create a favorable atmosphere in the room. In summer, the air conditioner will cool the air, and in autumn or spring it will heat it up. In any case, it will be comfortable to be in the room.
  • Clean indoor air. This is especially true for residents of large cities living in industrial areas. Using an air conditioner will allow you to get cool, clean air without opening windows.
  • Maintaining optimum air humidity. Some models have a dehumidification function, creating an optimal level of humidity in the room.


Please note that the air conditioner can harm a person only if used improperly. If the unit is not cleaned regularly, harmful bacteria and viruses can begin to multiply in it.

Due to the nature of the air conditioner, the air in the room becomes drier, so we recommend using separate devices that increase the level of humidity in the room.

The compressors make a little noise during operation. Usually the compressor is located in the outdoor unit, and you can not hear how it works in the room.

Maintenance and repair

It is necessary to clean the air conditioner regularly and carry out preventive maintenance to ensure that all systems work properly. You can clean the filter yourself, knowing the device of the model or call a specialist who can handle it in 30-60 minutes.

If the air conditioner breaks down, do not repair it yourself, call the service department and describe the problem. Sometimes breakdowns are solved within a few hours on the spot. For example, if the split system shuts down due to overheating after a long period of operation, the reason is most likely a compressor overheating or a dirty radiator. The problem is solved by cleaning the grate.

If the unit is not running at full capacity, check the air filters. Perhaps they need to be cleaned.

Schematic diagram of the air conditioner

Like any other technical device, the air conditioner has a circuit diagram, which shows all its components, as well as communications - that is, the connections between them.

Conventionally, the air conditioner can be divided into two functional parts:

  • refrigeration circuit
  • electrical part

The main function - cooling, is carried out by the refrigeration circuit, but all its components are controlled by an electrical circuit (electronic).

In this article we will consider the circuits of non-inverter air conditioners.

Diagram of the refrigeration circuit

Below is a diagram of the refrigeration circuit of the air conditioner.

The diagram is not taken from a textbook, but from the manufacturer's service documentation, therefore the symbols are given in English.

Compressor - compressor, "the heart of the air conditioner". The compressor compresses the refrigerant and pumps it around the circuit.

Heat exchanger heat exchanger

  • indoor unit - indoor unit - evaporator, in which the working substance evaporates, lowering the temperature
  • Expansion valve - expansion valve

    In another way, TRV is a thermostatic expansion valve. Provides the required amount of refrigerant.

    In simple air conditioners, its role is performed by a capillary tube, without any adjustment, in inverter systems, by an electronic expansion valve.

    2-way valve - a two-way valve, that is, a conventional gate valve, with two positions - open and closed

    3-way valve pressure or filling.

    4-Way valve - a four-way valve that provides refrigerant reversal for air conditioner operation in heating mode

    Strainer - operate in reverse mode and the refrigerant changes direction).

    Its task is to prevent moisture from entering the thin channel of the expansion valve - as moisture will clog it, preventing the refrigerant from passing through.

    Muffler - muffler

    Arrows indicate the direction of freon movement along the circuit:

    • solid arrow - in cooling mode
    • dotted arrow - in heating mode

    Also installed in more complex and advanced air conditioners:

    • pressure sensors
    • liquid separators
    • bypass lines
    • injection systems (injection) in the compressor
    • oil separators

    Scheme of a multi split system

    Multi split system is an air conditioner with one outdoor unit and several indoor units

    In this case, several more indoor units are added, as well as: refrigerant and sends it to several indoor units.

    The circuit also contains elements that are used not only in multi systems:

    Receiver tank - receiver.

    The receiver has several purposes - protection against compressor water hammer, freon drain during repairs, etc.

    In this case, this is a linear receiver that prevents gaseous freon from entering the expansion valve

    Electrical diagram of the air conditioner block.

    N - electrical neutral

    2 - compressor power supply from indoor unit control board

    3 - fan motor power supply for 1st speed operation

    power supply fan motor for 2nd speed operation

    5 - power supply to the four-way valve actuator for switching to heating mode


    Fan motor - motor, fan motor

    Thermal protector - protection against overheating, usually placed directly on the motor windings and breaks the circuit when the temperature is exceeded.

    Fan motor Capacitior - fan motor operating capacitor

    SV - solenoid valve - solenoid valve that drives the four-way valve mechanism.

    Air conditioner indoor unit diagram:

    Terminal block

    In addition to the interconnects, the terminal block also has clamps for connecting power (power can be supplied and vice versa - to the external unit)

    L, N - electric line and neutral of single-phase power 2 Filter Board - filter board, reduces the level of interference in the power supply

    Control Board - control board - controls all devices, receives data from all sensors, performs thermal control, displays information for the user on the display, performs self-diagnosis.

    Main relay - main relay - a power relay that supplies voltage to the compressor.

    Display board - display module, can be a line of LEDs that show the presence of power, the selected mode, an error code or a display that also displays the temperature.

    Thermistor - thermistor, thermistor, temperature sensor

    Room temp. - room temperature sensor

    Pipe temp. - temperature sensor of the heat exchanger tube, evaporator

    Temperature sensors can also be located in:

      • control panel - to maintain the temperature at the point where the control panel is located (for example, "I Feel" mode).
      • at the inlet, outlet and midpoint of the evaporator

    Step motor - step motor,

    It is used to open louvres, shutters that cover the fan

    In one step, its shaft deviates by a small angle, thus it is possible to control the position of the shaft very precisely.

    Drain pump motor - drain pump built into cassette units only

    Float switch - condensate level float switch only for cassette units

    Where can I get the diagram of my air conditioner?

    Air conditioner diagrams may differ for each specific model - somewhere there may be details that are not in the above diagrams (for example, sensors or protective devices), or vice versa, some details will not be.

    Learn more