How a Vehicle's AC Works

In the past, a car's air conditioning system often involved nothing more than cranking down the car's windows. In fact, it was common to see an AC system in only premium or fully-loaded vehicles.

Fortunately for today's drivers, this trend has changed.

Today, an AC system is one of the most common features in all automobiles. From compact cars to SUVs, finding a car today that is not equipped with an AC system would be a challenge.

How the AC Controls the Temperature

Most drivers are probably unaware of exactly how an AC controls the temperature inside a vehicle - all they know is the AC can cool the car on warm days and warm the car on cool days.

However, a vehicle's AC system actually goes through many steps in order to make one's daily commute more comfortable.

In fact, a vehicle's AC system does not even create cold air - it actually uses heated air from within the car to produce that cool or warm air blowing from the car's vents.

The process all starts with the vehicle's compressor, a large central component that serves as the system's refrigerant pump. The compressor compresses the refrigerant, or coolant, within the system and then circulates the high-pressure, high-temperature gas through the condenser, which puts the gas in contact with the fresh air outside of the vehicle. This fresh air then absorbs the heat from the gas, causing the refrigerant to liquefy.

The cool but still high-pressure liquid then flows to the vehicle's evaporator, where the liquid turns into vapor. This cool vapor is what the vehicle's fans then blow threw the interior vents, controlling the temperature in the car's cabin.

This entire system relies on the use of compressible gases, such as Freon. In the past, the type of Freon commonly used in vehicles was called R-12, which was found to be very harmful to the Earth's ozone layer. The gas could not be exposed to the air so servicing a car's air conditioning system required access to special machines that prevented the Freon from escaping into the atmosphere.

Today, newer cars use a new refrigerant, called R-134a, which is not dangerous to the ozone layer. The AC system in many older cars also can be converted so they can run on the newer R-134a coolant versus the more dangerous R-12 coolant.

Types of Vehicle AC Systems

While most cars today are equipped with AC systems, not all AC systems are the same.

There are two primary types of AC systems found in vehicles: an open loop system and a closed loop system.

The most basic system, the open loop system essentially does not take into account the actual temperature output of the air conditioning. These systems often give drivers two options: 1) cool or warm air and 2) the amount of air blown from the vents. With an open loop system, it might take more heated air to warm the car to 75 degrees on a cool day versus a warm day.

In contrast, the closed loop system is more sophisticated. This system constantly measures and adjusts the output temperature in order to maintain a constant output at the desired temperature. With a closed loop system, drivers often can select the actual temperature they want the car's cabin to be and the AC then will adjust the air temperature accordingly.