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Understanding Car AC Systems: Basics & Maintenance Tips
When asked how car air conditioning systems work, most people would respond, “I don’t care how they work, I just want them to work!” While that may be a common response, it does not answer the question.
Car air conditioning systems work by manipulating refrigerant between a liquid and gaseous state to absorb heat and humidity from the vehicle and provide cool, dry air. The refrigerant used in automotive air conditioning systems has transitioned from R-12 (Freon) to R-134a and now to R-1234yf, which produces fewer greenhouse gases.
The main components of a car AC system include the compressor, condenser, dryer, metering device and evaporator, each with its own role in the cooling process. Common failures in car AC systems include leaks, which can damage the compressor, and reduced airflow through the condenser due to road debris and dirt. Automotive AC technicians diagnose and repair AC systems, making it a valuable skill for a career in automotive technology.
If you are someone who has always been curious about how car AC works, continue reading below for a deeper look into air-conditioner theory, system components and system operation.
How Does Car AC Work?
The air conditioning system in a car works by manipulating refrigerant between a liquid and a gaseous state. As the refrigerant changes states, it absorbs heat and humidity from the vehicle and allows the system to give off cool, dry air.
To change the refrigerant between a liquid and a gaseous state, the air conditioning system works to control pressure and temperature.
AC System Refrigerants
In the past, automotive air conditioning systems used R-12 as the refrigerant. R-12 (aka Freon) is a very effective CFC-based (chlorofluorocarbon) refrigerant that is not flammable and not poisonous to humans. During the late 1980s, scientists discovered that widespread use of R-12 was damaging the earth’s ozone layer.
Manufacturers transitioned to R-134a in the mid-1990s. R-134a is an HFC-based (hydrofluorocarbon) refrigerant that does not have the ozone-destroying properties of Freon. The newest refrigerant is R-1234yf, which produces fewer greenhouse gases. Europe requires the use of R-1234yf, and it will likely become the new standard in the United States.
How to recharge a car AC? If the AC system of a vehicle stops working efficiently, a technician can recharge the system with a new refrigerant.
Car AC System Parts
Automotive air conditioning systems have a few key components. Listed below are the main parts and their roles:
Compressor
- Power unit of the system that separates the low-pressure side from the high-pressure side.
- Takes in low-pressure gas and compresses it into high-temperature/high-pressure gas.
- Mounted to the front of the engine and driven by the serpentine belt.
Condenser
- Reduces the temperature of refrigerant while it maintains high pressure.
- Refrigerant changes from a gaseous state to a liquid state as it cools.
- Like the engine radiator, it uses forced air (fan or vehicle movement) to transfer heat.
- Mounted in front of the vehicle, behind the grill.
Dryer
- Removes water from the refrigerant using a desiccant (drying agent).
- Has some system-filtering properties.
- Mounted on the high-pressure side of the system, between the condenser and metering device.
Metering device
- Either expansion valve or fixed orifice tube.
- Lowers refrigerant pressure, which quickly drops the refrigerant temperature.
- Refrigerant is still in liquid form after leaving the metering device.
- Mounted on the high-pressure side of the system, between the dryer and firewall.
Evaporator
- Refrigerant changes back to a gaseous state in the evaporator, causing a cooling effect.
- Cabin air is cooled and dried as it blows across the evaporator.
- Only component mounted inside the passenger compartment, behind the dashboard.
Path and characteristics of refrigerant
- Low-temperature/low-pressure refrigerant enters the compressor (gas).
- High-temperature/high-pressure refrigerant leaves the compressor (gas).
- Refrigerant cools and converts to liquid in the condenser.
- Still under high pressure.
- The receiver/dryer removes water from the refrigerant.
- Expansion valve reduces refrigerant pressure.
- Refrigerant converts back to a gaseous state in the evaporator.
- Absorbs heat; when air blows across the evaporator, it is cool and dry.
AC system diagram
Below is an AC system diagram that shows the main components used and how they’re connected:
Common AC System Failures
Because automotive air conditioning systems operate under pressure, they need to remain completely sealed from the surrounding environment. Anything that allows refrigerant to escape or contaminants to enter can cause a failure.
If a leak is present in any component, simply recharging the system with new refrigerant will be at best a temporary fix. Identify the leak, replace the faulty component and then evacuate and recharge the system.
Not only will a system leak stop the AC system from cooling, but it can also damage the compressor. The compressor can overheat and damage itself by trying to run with too little refrigerant in the system. Compressors generally are not serviceable and are an expensive item to replace.
To operate correctly, the AC condenser needs a steady flow of air through its fins. Road debris and dirt may reduce airflow, causing system malfunction. The condenser is mounted directly behind the vehicle grill, leaving it somewhat exposed and at risk for partial blockage.
What Does This Mean for Your Career?
Almost every new car sold in the U.S. is equipped with an air conditioning system. What was once considered a luxury is now an expectation. Automotive AC technicians diagnose and repair AC systems on a regular basis at dealerships and independent shops. Technicians often hear customers complain about warm air, loud noises and even water leaking inside the car!
AC Systems FAQs
How does a car air conditioner work?
The AC in a car cools the air through the vehicle’s compressor. The compressor helps raise the pressure and temperature of the refrigerant. From the compressor, the process moves on to the receiver which is responsible for removing extra moisture and other contaminants.
What are the main components of a car air conditioning system?
These are the main components of an AC:
- Compressor
- Condenser
- Evaporator
- Receiver-dryer
- Expansion valve
How does the refrigerant in a car air conditioner cool the air?
The refrigerant that passes through the evaporator changes from a liquid to a gaseous state, which causes a cooling effect. Air is forced through the evaporator and the refrigerant absorbs heat from the air as it passes through. The air that emerges from the evaporator is cooler and drier than it was when it approached the evaporator.
Train To Become an Automotive Technician
Does an automotive technician career sound like the right fit for you? Students at Universal Technical Institute (UTI) learn about every system of a vehicle, including air conditioning.
In less than a year, you can gain the skills and knowledge needed to pursue an entry-level position.1,7 To learn more, visit our program page and request information to get in touch with an Admissions Representative.
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