July 5, 2019

How Your AC System Works

A lot has changed in the 100 plus years since the invention of the first modern air conditioning system. However, today’s central air conditioners still work using many of the same basic principles. So how does a central air conditioner work?

How an Air Conditioner Actually Cools Your Home

An air conditioning system doesn’t create cold—it moves heat from inside your home to the outside. That cooling happens through a closed loop called the refrigeration cycle, which uses a refrigerant and four main components to absorb indoor heat and reject it outdoors. Understanding the basics helps you recognize issues early and get the most efficient performance from your system.

  • Compressor: Often called the heart of the system, the compressor squeezes the low-pressure refrigerant gas, raising its pressure and temperature so it can release heat when it moves to the condenser.
  • Condenser: Located outside, the condenser coil releases the heat the refrigerant picked up inside. As the hot, high-pressure gas passes through, it cools and condenses into a liquid.
  • Expansion device (or metering device): This component (like a thermal expansion valve or capillary tube) reduces the pressure of the liquid refrigerant, causing it to cool rapidly before entering the evaporator.
  • Evaporator coil: Inside the home, the cold, low-pressure refrigerant absorbs heat from the return air blowing over the coil. That heat turns the refrigerant back into a gas while the cooled air is circulated into living spaces.
  • Air handler / blower: Moves indoor air across the evaporator coil to deliver cooled air into rooms and pulls return air back into the cycle.
  • Refrigerant: The working fluid that cycles through these components, changing between gas and liquid to transfer heat efficiently.

In short: the compressor pressurizes refrigerant, the condenser dumps heat outside, the expansion device cools it down, and the evaporator pulls heat from inside your home. The cycle repeats, keeping your space comfortable. Regular maintenance ensures each component operates correctly and avoids breakdowns.

The Science of Heat Transfer

The job of an air conditioner is to transform warm air in cool air, but it does not actually make cold air. Instead, it removes the heat and humidity from the warm air, transfers it outside, and then returns cooled air back into the house. This entire process is made possible through the science of heat transfer, refrigerant, and an air conditioner’s three main mechanical components:

  • Compressor unit
  • Condenser coil
  • Evaporator coil

Refrigerant is a special chemical that travels through the air conditioner’s tubing. As the refrigerant passes through to the compressor, it is put under pressure, which raises its temperature and converts it to gas. The gas continues to travel outdoors to the air conditioner’s condenser coil where the heat disperses across its aluminum fins.

As the heat disperses from the refrigerant in its gaseous state, its temperature drops, and it returns to its previous liquid state. The refrigerant then travels along with the tubing back indoors to the evaporator coil. This is where the liquid evaporates and cools the coil. The air conditioner’s fan then blows the warm air that is brought in from the system’s return vents. The refrigerant absorbs the heat from the warm air, and the now cool air is blown through the system’s ductwork to its air vents.

A Continuous Cycle Until Something Goes Wrong

The process of recirculating an air conditioner’s refrigerant is a continuous cycle. It continues until the air in the home reaches the temperature set on the thermostat. Of course, this process can only be successful if all the components in the HVAC system are working properly.

To ensure that your air conditioner is ready when you need it, the system requires regular yearly maintenance. In the St. Louis metro area, Scott-Lee Heating Company is the heating and cooling expert to call for all your cooling maintenance needs and repairs.