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How do Air Conditioners Work?

A collage of air conditioners.

Modern air conditioning systems work as reverse heat pumps. An air conditioner provides cold air inside an enclosed space by actually removing heat and humidity from the indoor air. It returns the cooled air to the indoor space, and transfers the unwanted heat and humidity outside.

The technology has been around for over a century, but few people really understand the basics of how their air conditioners work. By learning about the overall way your system operates, you’ll be able to understand and keep up with maintenance on it.  

Air Conditioning Overview

A couple on sofa using air conditioner.

At the most basic level, air conditioning involves two components that work simultaneously. One of these is located inside a building and is usually referred to as the inside unit. The outside unit is usually located outside the building on a concrete pad with some partial protection from the elements.

Inside the home, warm indoor air is cooled as it blows across a cold cooling coil that is full of refrigerant. The heat from indoor air is absorbed into the refrigerant as the refrigerant turns from liquid to gas. The cooled air is distributed back to the house.

Outside the home, the refrigerant gas enters a large coil in the outdoor unit while it is still compressed. As this refrigerant turns back into liquid, heat is released outside. A large fan will pull outdoor air through the outdoor coil, forcing the heat to dissipate into the outside environment.

This is a continuous cycle of heat and humidity being removed from indoor air, cool air returning to the home, and heat and humidity exiting the home.

Air conditioning systems include a number of components and do more than just cool the air inside. They can also control humidity, air quality and airflow within your home. Of course, to really understand how each component works, it’s a good idea to learn about all of its parts.

Parts of an Air Conditioner

Evaporative Coils

Air conditioner evaporative coil

As soon as air from inside enters the system through an air intake (this is the area where you change your filter), the air is forced to run over a set of evaporative coils. These coils will absorb the heat from the air and force the water or humidity in the air to condense.

Blower

The blower is essentially a big fan that pushes the air through the system. In very larger systems where air has to move through a significant amount of ductwork, it may be necessary to have multiple blowers.

Condenser and Compressor

Air conditioner condenser on roof deck.

The refrigerant in the evaporative coils becomes cold because it is forcibly condensed or compressed. As this happens, the refrigerant drops in temperature. The condenser is essentially a pump that forces the refrigerant to condense.  

As this refrigerant absorbs heat from the inside air, it travels to a coil in an outside unit where the heat allows the refrigerant to expand. This heat is then expelled into the outside environment, and the refrigerant is again condensed inside to cool down the air and start the cycle again.

Fan

The fan works with the blower to force air through the system and put into the room.

Filter

Woman removing air filter from the air conditioner.

When air first enters the system, it needs to be cleaned. The filter is one of the first things the air travels through, and its job is to remove particles or dust and dirt. Higher end filters may also remove biological particles such as pollen and mold spores.

Thermostat

Air conditioner thermostat

This device allows the user to set a temperature for the room. When the room reaches this temperature, the system automatically shuts off. It will come back on when the temperature increases.  

It’s important to realize that the thermostat does not tell the air conditioner to make the air colder. It does not co troll the speed or rate of the condenser, it can only turn it on and off.

Types of Air Conditioners

While air conditioning systems all operate on the same general principles, they do not all operate exactly the same. Because indoor living spaces come in a variety of shapes and sizes, residential, commercial, and industrial air conditioning systems are also available in different styles and configurations.  

There are three primary types – split-system air conditioner, packaged air conditioner, and ductless air conditioner. Each has its own specialized uses, but they all essentially do the same thing.  The type of cooling system that works best for a particular building will depend on the geographical location, the size and physical limitations of a building and the way it is used.

Split-System Air Conditioner

Split system air conditioner

Split-system air conditioners offer the most common answer to the question, “what is central air?” These systems include both an indoor unit and an outdoor unit. The indoor unit, typically a furnace or a fan coil, includes the evaporator coil and blower fan (air handler) that circulates air throughout the home. The outdoor unit holds the compressor and the condenser coil.

Split-system air conditioners provide a variety of options, including basic single-stage systems, quieter and more efficient two-stage systems, and the quietest, most energy-saving multi-stage systems. A split system air conditioner offers consistent, reliable temperature control to the entire home. And, because the system uses filters in the indoor air handler, it can clean your air while it cools it.

Packaged Air Conditioner

Packaged air conditioner outside the home.

Packaged systems are all-in-one solutions that tend to work best in small spaces. Packaged systems contain the evaporator coil, blower fan, compressor and condensing coil all in one unit. They work well in areas such as an attic or closet. They are also a good choice in areas where rooftop installations are preferred.

Like split systems, packaged systems pull warm air from the home, through return air ducts, into its evaporator coil section. The air passes over the evaporator coil and the cooler air is returned to the building through supply air ducts. The unwanted heat is released to the outside through the condenser coil.

Packaged systems also offer a variety of options to provide better energy efficiency. Most people think of the window-box type units that are common in many stores, but they also come in models that can be attached to a wall (although warm air must be vented to the outside of a room through some sort of hole, which may sometimes need to be cut in order to properly install one of these systems.)  

They are available in two-stage systems and single-stage systems. Higher efficiency models include multi-speed blower fans. In the United States, packaged systems are most common in the south and southwest areas of the country.

Ductless Air Conditioner

Ductless air conditioner mounted outside the home

Ductless systems are not considered to be central air systems because they deliver cooling to specific, targeted areas within a building. They require less invasive installation because they don’t rely on ductwork to distribute chilled air.

Like split systems, ductless systems include an outdoor unit and at least one indoor unit, connected by copper refrigerant tubing. In a ductless system each indoor unit is designed to provide cool air only for the room in which it is installed. The indoor unit can be installed on a wall, ceiling, or floor.

Many ductless systems include multiple indoor units connected to one outdoor unit. This makes them ideal for large office buildings and event spaces. Regardless of the number of indoor units, the operation is similar to a split system. The indoor unit contains an evaporator coil and blower fan to pull warm air from the room, across the cool evaporator coil, then return the cooler air back into the room.

Refrigerant runs through the copper tubing to the outdoor unit where the compressor and condenser coil are located. Heat from inside is released through the outdoor condenser coil. Refrigerant returns to the indoor unit, and the cycle continues.

These flexible systems deliver cool air only in the areas where these units are placed. They also act like a zoning system by offering individual temperature control over each separate room. 

Regardless of which type of system works for your home or property, knowing how your air conditioner works is an important way to perform basic maintenance and understand the repairs that are necessary when your HVAC technician visits your home or office.