How Auto Air Conditioning Works — A Layperson’s Guide

How Auto Air Conditioning Works in Simple Terms

If you’ve ever turned on your AC and been greeted with a blast of warm air, you’ve probably asked yourself: what went wrong? After decades of repairing vehicle climate control systems, I can tell you firsthand that understanding how auto air conditioning works isn’t just for professionals. It’s something every car owner should know. When you grasp the basic operation and layout of your AC system, you’re in a much better position to spot issues early and avoid expensive repairs.

In this article, I’ll explain how auto AC systems work, the major components involved, where they’re located, and the most common problems that can cause your car’s air conditioning to stop blowing cold air.

Auto Air Conditioning Doesn’t Make Cold Air; It Just Transfers Heat From the Cabin to The Outside

Air conditioning, whether in your car or home, isn’t about producing cold air; it’s about removing heat from inside the house or car and moving it outside. Cold isn’t something you create—it’s simply the absence of heat. Refrigeration is all about moving heat from one place (your car’s cabin) to another (outside the vehicle).

The Major Components of a Car AC System and Where They’re Located

Here’s a breakdown of the key parts of the system:

Compressor— The compressor is usually located at the front of the engine and driven by the serpentine belt. However, many hybrids and all EVs use an electric compressor, which is also located under the hood. The compressor is the heart of the system. It compresses low-pressure refrigerant vapor and turns it into a high-pressure, high-temperature gas. This is where the cooling cycle begins.

Condenser — Found in front of the radiator, the condenser is responsible for removing heat from the refrigerant. As hot high pressure refrigerant vapor from the compressor flows through it, airflow across the condenser cools the refrigerant, causing it to condense from a gas into a high-pressure liquid.

The Auto AC condenser sits in front of the engine’s radiator

Receiver-Drier or Accumulator— Most systems with a thermal expansion valve use a receiver-drier, which is typically mounted near the condenser. However, systems with an orifice tube use an accumulator, usually located near the firewall. These components store and filter the refrigerant and remove moisture.

Expansion Valve or Orifice Tube—Located just before the evaporator, this component controls the flow of high-pressure liquid refrigerant into the evaporator core. It drops the refrigerant’s pressure, allowing it to evaporate and absorb heat.

Evaporator— Mounted inside the dashboard or HVAC

Evaporator core

housing behind the glovebox, the evaporator is where the magic happens. The blower motor forces warm cabin air through the evaporator core. The liquid refrigerant inside in the evaporator absorbs the heat from the cabin air, causing the liquid refrigerant to boil and turn from a liquid to a gas. In simpler terms, this process is like using the heat from your stove to boil water, turning it from a liquid into steam.

Once you understand how each of these parts fits into the system, it becomes easier to understand how auto AC systems work as a whole.

How Auto Air Conditioning Works—Step by Step

Let’s walk through the process so you can see exactly how auto air conditioning works in real time:

1) The compressor kicks on, compressing low-pressure refrigerant gas vapor into a high-pressure vapor.

2) The hot refrigerant vapor travels to the condenser. There, outside airflow flows across the condenser, cooling the 150°F refrigerant vapor, causing it to condense into a high-pressure liquid.

3) The refrigerant passes through the receiver-drier or accumulator, which filters out moisture and contaminants.

4) The high pressure liquid refrigerant then flows through a metering device like an expansion valve or orifice tube and then into the evaporator.

5) The blower motor forces hot cabin air across the evaportor fins, heating the liquid refrigerant until it boils and changes from a liquid into a gas. In other words, an auto AC system uses cabin heat to boil the refrigerant, so it’s now cooler, resulting in cold air blowing into the cabin.

6) Meanwhile, the refrigerant vapor returns to the compressor and the cycle repeats.

That’s the full loop. And that’s exactly how auto AC systems work to keep your car cool on even the hottest days.

The Most Common Problems That Kill Auto Air Conditioning Systems

Knowing how auto air conditioning works helps you diagnose what might be going wrong when your AC starts acting up. Here are the most common issues I see:

Low Refrigerant Charge— This is by far the number-one issue. All auto AC systems are sealed. However, over time the hoses and seals can age and leak. In addition, corrosion and road impacts can damage the condenser and evaporator, causing leaks. Once refrigerant levels drop too low, the system either stops working or blows warm air. If your compressor cycles on and off rapidly, low refrigerant is a likely cause.

IMPORTANT: Once an auto AC system leaks, it not only loses refrigerant, but also lubricating oil. Adding more refrigerant without also adding oil is the #1 cause of compressor failure.

Compressor Failure— Compressors wear out, especially if the system runs low on refrigerant or oil. You may hear loud clicking, grinding, or feel no cooling at all. Without a working compressor, nothing else in the system matters.

Clogged Expansion Valve or Orifice Tube— Debris from a worn out compressor and aging rubber hoses can restrict refrigerant flow into the evaporator, causing high pressure on one side of the system and no cooling on the other. This is more common after a compressor failure, where metal particles can contaminate the system.

Clogged Condenser— Since the condenser sits in front of the radiator, it can easily get clogged with bugs, pollen, dust and dirt that restrict the flow of air across the condenser. A restricted airflow reduces refrigerant cooling and condensation, resulting in warmer air.

©, 2025 Rick Muscoplat