How Your Car’s AC Works

Surely you know what air conditioning is, but do you know how it works? Contrary to what you might expect, AC systems do not create cool air. Instead, they cool the air by removing hot air and moisture.

The system conditions the air by cooling it and removing moisture to make you more comfortable while you drive. There are three types of air conditioning systems: orifice tube systems or expansion valve systems or a combination of the two which is found in rear air conditioning systems. The air conditioning system is made up of the following components: compressor, condenser, evaporator, orifice tube (or expansion valve), and an accumulator (or receiver-drier). Each of these components serves a different purpose. Learn more about the repetitive cycle of the system from the list of air conditioner components and the AC parts diagrams below.

How Does a Car’s Air Conditioning Work?

Any AC system requires a refrigerant, such as R-134a. Your vehicle’s compressor, powered by the serpentine belt, compresses the refrigerant into a liquid, putting it into a high-pressure state. This pressure forces the liquid out of the compressor through the hoses in your AC hose assembly, which carry refrigerant through the system. Regardless of which of the systems your car uses, the compressed refrigerant travels from the compressor to the condenser on the high-pressure side of the system to cool off before reaching the AC evaporator core on the low-pressure side.

The condenser is like a small radiator where the AC hoses come in contact with the outside air, which absorbs heat from the liquid inside before the liquid reaches the AC in-line filter, which removes debris that could contaminate the system. The now cooled refrigerant moves to the low-pressure side of the system through either the expansion valve or the orifice tube, depending on which system you have. There it goes through the evaporator core in a gaseous state, allowing the refrigerant to absorb heat from the air that passes through the evaporator fins. This leaves the cabin with cool air while the warm refrigerant makes its way back to the compressor.

Scroll down to see a step-by-step breakdown of how refrigerant travels through your car’s AC parts.

*Air conditioning systems will use either an orifice tube/accumulator or an expansion valve/receiver-drier set up. Some vehicles that have a rear AC system can use a combination of the two with an additional evaporator.

Automotive AC System Components

1. The System is Filled with Refrigerant

The refrigerant gas used in most vehicles is commonly known as Freon or R134A. Prior to 1994 R12 was used in air conditioning systems, but was discontinued due to the highly polluting nature of the gas. The ability of the refrigerant to change its physical properties as it is compressed, cooled and metered is what makes the AC system work.

2. The Refrigerant is Turned into Liquid by the Compressor

The compressor is responsible for compressing the refrigerant gas, commonly known as Freon. When the gas is compressed it becomes very hot and is then sent through a condenser.

3. Refrigerant is Cooled in the Condenser

The condenser is a series of coils that outside air passes over to remove the heat from the compressed gas. This will cause the gas to cool and condense into a cold liquid.

  • A parallel style (non-serpentine) condenser cannot be flushed and must be replaced if it fails.
  • A serpentine-style condenser can be identified by inspecting the ends of the component and observing a snake like appearance that indicates a long singular tube that switches back several times almost like a ribbon. This style condenser can be flushed using the AC Flush Kit available in the AutoZone Loan-A-Tool program.

4. Air is Dried in the Receiver-Drier*

The receiver-drier is a canister that contains desiccant inside to absorb moisture. The receiver-drier sometimes has a sight-glass on top to observe flow (however, on retrofitted systems the sight glass will be rendered useless since the oil used with R134A is not transparent), while an accumulator will not.

*In expansion valve and receiver-drier systems

5. Debris is Removed by the AC Inline Filter

The AC Inline Filter Kit traps debris that even flushing cannot remove from your AC lines.

6. The Liquid Refrigerant is Turned into Mist by the Expansion Valve*

The expansion valve provides a restriction in the flow of refrigerant. This restriction causes the refrigerant to change from a high-pressure liquid refrigerant into low-pressure liquid refrigerant mist before it enters the evaporator. The failure of an expansion device is usually restricted flow due to clogging.

*In expansion valve and receiver-drier systems

7. …or by the Orifice Tube*

The orifice tube has a conical shaped fixed orifice that provides restriction in the flow of refrigerant. This restriction causes the refrigerant to change from high pressure liquid refrigerant into low pressure liquid refrigerant mist before it enters the evaporator. The failure of an orifice tube is usually restricted flow due to clogging.

*In orifice tube and accumulator systems

8. The Mist Removes Warm Air from the Cabin in the Evaporator

As the low-pressure liquid refrigerant mist flows through the evaporator, a blower motor pushes air across the cold tubes of the evaporator to deliver cooled air into the passenger compartment of the automobile.

9. Moisture is Removed from the Mist by the Accumulator*

The accumulator is a holding tank for the refrigerant exiting the evaporator. While the refrigerant is circulating inside, the accumulator desiccant bag removes any moisture that may be present.

*In orifice tube and accumulator systems

Two Common A/C Systems

Orifice Tube and Accumulator System

This type of system features an orifice tube before the evaporator core and an accumulator before the compressor. The orifice tube restricts the refrigerant flow, changing the high-pressure liquid to a low-pressure mist before entering the evaporator. The accumulator is a holding tank with a desiccant bag to remove any moisture from the refrigerant before it reaches the compressor.

Expansion Valve and Receiver-Drier System

This system has a receiver-drier between the condenser and the in-line filter kit and an expansion valve before the evaporator core. It contains desiccant to absorb moisture like the accumulator does, but the receiver-drier is located on the high-pressure side instead of the low-pressure side. The expansion valve plays the same role as the orifice tube in that it restricts refrigerant flow to allow the pressurized liquid to expand into a low-pressure mist.

Now that you know how your AC system works, check out our other air conditioning guides like How to Recharge Your Car’s AC or Diagnosing AC Problems. You can get the parts you need at your local AutoZone Store.
If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

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Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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