There are so many parts and components that comprise an HVAC system. And in order for an HVAC system to work perfectly, each of these parts and components has to be in perfect condition as well. Out of all the HVAC parts and components, one that is incredibly important — especially for air conditioners — and needs a lot of extra attention is the compressor.

What Is an Air Conditioner Compressor?

By definition, the word “compress” means “to reduce in size, quantity, or volume as if by squeezing.” And so, using that definition, we could define an air conditioner compressor as a component that is used to remove the heat-laden vapor refrigerant from the evaporator of the air conditioning systems. In other words, the compressor compresses or squeezes the vapor into a smaller volume at a high temperature.

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How Does an Air Conditioner Compressor Work?

In order to fully understand how an air conditioner compressor works, one must first be aware of the refrigeration cycle. Simply put, refrigeration is the process of cooling a space, substance, or system to lower and/or maintain its temperature below the ambient one (while the removed heat is rejected at a higher temperature). Basically, refrigeration is an artificial or man-made kind of cooling. And refrigeration is the process that allows air conditioners to operate and remove heat from inside a building and carry it outside, thus cooling the indoor temperature.

The way the refrigeration cycle for air conditioners works is that first, the refrigerant absorbs heat from a room in the evaporator coil, causing it to change from a cold liquid to a low-pressure, warm refrigerant gas. This is then where the compressor comes in: it squeezes the refrigerant gas, thus reducing its volume and turning it into a high-pressure, hot gas. This hot gas enters the condenser, and when that happens, outside air flows over it, which removes heat and results in a high-pressure, cool liquid. And finally, the expansion valve lowers the pressure and temperature of the liquid refrigerant, turning it into a cold gas and sending it back to the evaporator. This process repeats itself for as long as the air conditioner is turned on.

Related Article: Top Components in a Refrigeration System

What Are the Types of HVAC Compressors?

HVAC compressors can be categorized by their application. There are five types of compressors that are used in air conditioning units. They are as follows:

Reciprocating Air Conditioner Compressor

The reciprocating compressor is actually the most popular type of air conditioner compressor. This kind of compressor uses a piston to compress the air by moving the piston up and down inside the cylinder. As the piston moves down, it creates a vacuum effect that sucks in the refrigerant. And as it moves up, the gas compresses and moves into the condenser.

More often than not, reciprocating air conditioner compressors can have multiple cylinders inside. In fact, it is common to find reciprocating air conditioner compressors that have two cylinders, even four and eight. Because of this, this kind of compressor is incredibly efficient. And for that reason, it can be used in appliances, residential air conditioners, light commercial air conditioners, commercial air conditioners, refrigeration, and industrial applications.

Diaphragm Compressor

The diaphragm compressor is a somewhat specialized reciprocating design. It uses a motor-mounted concentric that oscillates a flexible disc which alternately expands and contracts the volume of the compression chamber. Very much like a diaphragm pump, the drive is sealed from the process fluid by the flexible disc, and so, there is no possibility of lubricant coming into contact with any gas.

Diaphragm air compressors are relatively low-capacity machines that have applications where very clean air is required, like in many laboratory and medical settings.

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Scroll Air Conditioner Compressor

A scroll air conditioner compressor, also known as a scroll pump or scroll vacuum pump, has one fixed scroll that remains stationary and another moving or orbiting scroll that rotates through the use of swing link. When this happens, the pockets of refrigerant between the two scrolls are slowly pushed to the center of the two scrolls, thus causing the reduction of the volume of the gas. After, the gas is then discharged through the center port to the condenser.

The advantage of the scroll compressor is that it has fewer moving parts and less torque variation compared to the reciprocating compressor. This advantage is translated into a smooth and quiet operation. As a result, scroll compressors are quickly becoming as popular as reciprocating compressors even though they are relatively new on the scene.

Screw Air Conditioner Compressor

The screw air conditioner compressor uses a pair of helical rotors where it traps and compresses the gas as the rotors revolve in the cylinder. The male rotor and the female rotor are built inside the cylinder. The low-pressure refrigerant enters one end of the compressor, and the resultant high-pressure refrigerant is discharged into the opposite end to the condenser. In other words, a screw air conditioner compressor contains two large helical rotors that move the air from one to the other. And as the refrigerant moves through the compressor, the space gets smaller, and it gets compressed.

Because of the design of the screw compressor, it is actually extremely reliable and efficient. However, it is only mainly used in large buildings where there is a vast amount of air that requires continuous cooling.

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Sliding Vane Compressor

A sliding vane compressor relies on a series of vanes that are mounted in a rotor and sweep along the inside wall of an eccentric cavity. The vanes rotate from the suction side to the discharge side of the eccentric cavity, and as they do this, they reduce the volume of space they are sweeping past, thus compressing the gas trapped within the space. The vanes then glide along on an oil film that forms on the wall of the eccentric cavity, providing a seal.

Sliding vane compressors can’t be made to provide oil-free air, but they are capable of providing compressed air that is free of pulsations. Additionally, they are also forgiving of contaminants in their environments, owing to the use of bushings rather than bearings and their relatively slow-speed operation compared to screw compressors. Sliding vane compressors are also relatively quiet, reliable, and capable of operating at 100% duty cycles. For this reason, they are used in many non-air applications in the oil and gas and other process industries.

Rotary Air Conditioner Compressor

The rotary compressor can be divided into two types. One has blades or vanes that rotate with the shaft while the other type has the blade that remains stationary and is part of the compressor housing assembly. In both types, the vapor from the suction line is drawn into the cylinder through the suction port.

As the blade rotates, trapped vapor in the space ahead of the blade is compressed into high-pressure gas after which it is discharged to the condenser through the exhaust port. For this kind of compressor, the number of blades can range from two to eight in a single system.

Rotary compressors are small and quiet. Because of this, they are popular in locations where noise is a concern.

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Centrifugal Air Conditioner Compressor

A centrifugal air conditioner compressor is usually used in large capacity refrigerating systems. In this compressor, the vapor is moved in a circular motion known as centrifugal force. An impeller, which is a disk with radial blades, spins rapidly inside the compressor, thus causing the gas to gain velocity.

A diffuser converts this energy into pressure energy, and this energy is then discharged into the condenser. The pumping efficiency increases with speed, and so, this type of compressor is designed to operate at high speed.

The primary advantage of centrifugal compressors is that there are no valves, pistons, or cylinders. The wearing parts that need attention are the main bearings. Because of this, centrifugal compressors are the compressors of choice for extra-large HVAC systems.

Axial Compressor

The axial compressor achieves the highest volumes of delivered air, ranging from 8000 to 13 million cfm in industrial machines. Jet engines use this kind of compressor to produce volumes over an even wider range. To a greater extent than centrifugal compressors, axial compressors tend toward multi-stage designs, owing to their relatively low compression ratios. As with centrifugal units, axial compressors increase pressure by first increasing the velocity of the gas. And then they slow the gas down by passing it through curved, fixed blades, which increases its pressure.

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Protective Coating for HVAC Compressors

Because of the contribution that compressors offer to air conditioners, it is not a surprise that they are considered to be necessities for HVAC systems. For this reason, it is undeniably crucial that HVAC systems, especially air conditioners, are equipped with high-quality compressors. That is your primary job as an HVAC professional: to make sure that the compressors inside the HVAC systems you’re offering to your customers are of the best variety. And one thing that you have to do to achieve this task is to ensure that the compressors are painted with a protective coating.

As you’re already aware, surface roughness has a major impact on compressor performance. It is adversely affected by corrosion and fouling, which both reduce performance. Generally speaking, fouling the accretion of solids, usually polymers, on the internal surfaces of compressors, and, to some extent, steam turbines. There are various forms of fouling, but two of the most common ones are corrosion fouling and particulate fouling.

To begin with, corrosion fouling is a chemical reaction between the liquid in the gas and the airfoil. Many metals form an adherent oxide layer to passivate the surface and prevent further corrosion. The oxide layer usually exhibits high frictional properties.

On the other hand, particulate fouling is a buildup of small particles that are ingested by the compressor. These particles build up a kind of sand, distorting airflow and reducing the compressor’s capacity and efficiency.

With these problems that compressors are likely to experience, it’s important for compressors to have some sort of protective coating. Uncoated compressor components are far more susceptible to corrosion, erosion, and fouling, and understandably, you wouldn’t want any of that to happen to your compressors. The following are some of the most common coatings that are applied to compressors so as to avoid corrosion and fouling and to improve the compressors’ overall efficiency.

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Corrosion-Resistant Coating

This type of coating is self-explanatory: it’s the one with the primary goal of helping the compressors to be more resistant to corrosion. Naturally, this is the one that is the most commonly used out of all the protective coatings out there. You can easily find corrosion-resistant coating for compressors everywhere — there are so many companies that offer this product as well as service.

The corrosion-resistant coating usually comes in two kinds. The first kind is designed to improve surface finish as well as corrosion resistance. Meanwhile, the second kind is not only corrosion-resistant, but it is also specifically designed to reduce particulate fouling by providing release characteristics.

Organic Coating

These coatings contain carbon, refined, and/or modified petroleum products as well as different solvents, pigments, additives, and fillers. This category of coatings includes these following coatings:

Alkyd Coating

Alkyd coatings can be applied to prepared substrates in various environments. Depending on the ingredients incorporated, alkyds can stand up to different rigors in interior, exterior, underground, and underwater applications.

However, on the downside, alkyds use oxygen in order to complete the chemical reaction that turns them into durable finishes. And since oxygen needs to disperse throughout the paint film, these coatings take longer to dry, compared to other products.

Epoxy Coating Systems

Epoxies define a large, high-performance group of coating products, with excellent film-building, mechanical and chemical properties, as well as short curing and drying times. Epoxy coating systems can bond to different surfaces, including steel, zinc, aluminum, and galvanized components. This makes them the optimal choices for many industrial painting projects that demand maximum protection against normal wear and tear, abrasion, corrosion, moisture, water, salt air, fuels, and chemicals, as well as non-oxidizing acids, alkali, and salts in immersion.

Polyurethane Coating

Polyurethane coating products are enhanced with special additives, and so, they are characterized by an exceptional resistance to corrosion, abrasion, chemicals, and weathering processes. For this reason, they can fit a wide variety of industrial applications

Inorganic Coating

In order to provide protection against various stressors in industrial environments, inorganic coatings are formulated with ingredients like enamels, additives, and pigments. The following are three inorganic coatings that are commonly used in industrial applications.

Acrylic Coating

Although alkyd coatings are still dominant in many painting industries, waterborne paint coatings are currently gaining increasing acceptance for industrial and commercial applications. To provide adequate protection, acrylic coatings contain more binders and additives that are designed to high-performance standards and fewer pigment dispersants, surfactants, and rheology modifiers that negatively affect corrosion resistance.

Ceramic Coating

Simply put, ceramic coating is the process in which a coating of ceramic materials is applied to a metal surface to increase the strength of the machine part. In addition to corrosion protection capabilities, ceramic coatings are also known for their versatility of use on large components, ability to restore the surface finish, and low cost of application. In particular, ceramic coatings offer significant benefits in automotive applications because they reduce heat loss in automobile engines, exhaust manifolds, headers, turbocharger casings, downpipes, and many more. They can also provide thermal protection to several high-end automobile engines.

Because of all this, ceramic coatings can be found in places like high-performance automobiles. Additionally, they are also used for protecting automobile parts from the degradation of material composition due to friction that occurs during movement.

Intumescent Coating

Exposed to extreme heat or open flames, intumescent coatings expand into thick, foam-like layers that insulate structures from fire. Because these coatings can maintain the integrity of different components in case of fire, they are some of the best choices for high-heat applications.

Powder Coating

Powder coating involves the application of a dry powdered paint compound made of pigments, specialized resins, and fillers that melt and fuse together during the curing process to form a painted finish. The solid powder particles are electrostatically charged using a low-velocity air-powered spray gun. This electrostatic charge attracts paint particles to the substrate surface and holds them in place during the high-temperature curing process. The powder is usually used to create a hard finish that is tougher than conventional paint, which requires a solvent to keep the binder and filler parts in a liquid suspension form.

Powder coating can be relatively expensive, but it does offer a lot of benefits. In particular, it is high impact resistant, which means it eliminates chipping and scratching. As a result, it is commonly used for applications that involve impact and particle abrasion, and it extends the life of any machine in harsh environments.

Other benefits of powder coating include a variety of custom colors and textures (such as smooth, wrinkled, matte, and rough), resistance to heat, corrosion, impact, abrasion, most chemicals, and solvents, and resistance to fading from sunlight and UV exposure. Additionally, powder coating is also environmentally friendly because it doesn’t contain volatile organic compounds (VOCs), which are pollutants found in the solvents used in liquid paint finishes. As such, it eliminates the need for users to buy and maintain costly pollution control equipment, which saves money in the long run.

Because of the many benefits of powder coating, it is normally used in automotive applications, construction, architectural applications, electrical applications, farm applications, everyday household applications, manufacturing, and machinery.


In the HVAC industry, there are so many kinds of HVAC systems. And there are also so many kinds of HVAC components that comprise these systems. A popular kind of HVAC system is the air conditioner, and for this system, the compressor is one of the most crucial components. Generally speaking, an air conditioner compressor is a component that is used to remove the heat-laden vapor refrigerant from the evaporator of the air conditioning systems. In other words, the compressor compresses or squeezes the vapor into a smaller volume at a high temperature. This purpose solidifies the importance of compressors for air conditioners because without compressors, air conditioners will not be able to fulfill their duty of cooling an indoor space.

Because of the importance of air conditioner compressors, it is your duty and responsibility as an HVAC professional to make sure that the HVAC systems that you’re offering to your customers are equipped with high-quality air conditioner compressors. And one thing that you can do to achieve this task is to make sure that the compressors are coated with the right finish.

Applying finish coating to the air conditioner compressors is a necessary process because doing so helps prevent corrosion to the compressors. However, it can also be an extremely tedious process because there are so many things to consider. First, you have to do a proper surface preparation to the compressors, and then you have to go through a long list of possible protective coatings. And of course, before you decide on which protective coating to use, you have to test a variety of these protective coatings first to check their quality.

Long story short, it takes a lot of time and effort to choose the right paint for your air conditioner compressors. But the process has to be done so that you can provide air conditioner compressors that are of high quality to your customers.



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