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Understanding Vehicle Air Conditioning

For better understanding of working of Air Conditioner in our Cars. This Newsletter will give in depth understanding on parts that are in the AC system and the working of individual parts. There are some tips for effective working of AC.


Brief History on AirConditioning in Vehicle 


In early days , the automotive air conditioner was considered as a premium class and only the Rich could afford it. So, at that time, only about 20% of cars in the USA used to have it. However, in the late 20th century, the manufacturers widely started offering the car A/C. Today, almost every car has it.

On October 7, 1935, Ralph Peo of Houde Engineering, Buffalo, NY, applied for a patent for an "Air Cooling Unit for Automobiles". U.S. Patent was granted on November 16, 1937. In 1939, Packard became the first automobile manufacturer to offer an air conditioning unit in its cars.


First Cars with Air Conditioners 


Aftermarket AC system become highly popular after "would War II". Many independent manufacturers took this job of fitting aftermarket air cons into all makes of vehicles. These units were still pricey but there was a cheaper option knows as a car cooler. 

Car air conditioning systems have gained even popularity in the next decade. Several big automakers, including General Motors, stepped up to take the business away from independent manufacturers. They offered it as an extra option. 

However, GM made the air con as a standard feature in almost all of their models in 1953, and Nash and Pontiac followed the trend the next year. several other manufacturers followed suit in the next few years. 

Sales of AC units highly increased in the 60's. Cadillac really changed the game by bringing an AC control systems for the first time in 1964. The setting allowed changing the car temperature to a preferred temperature.





The car A/C works in two cycles: Refrigeration and Evaporative Cooling (evaporation and condensation). The main purpose of the car air conditioner is to make the cabin ambiance comfortable for the occupants.

Firstly, Air Conditioning is the process of making the air comfortable for the car’s occupants. The engineers achieve this by making changes in air’s properties. This mainly includes its temperature and humidity. An air conditioner is a device which changes and controls the properties of air. Basically, it improves the air quality and its thermal condition. A car air conditioner also does the same. Now, let’s understand the working of the Refrigeration Cycle employed in modern-day car A/Cs.

Just like the home A/C, the car air conditioner works on the same principle. It has the following main components:


  1. Compressor 
  2. Condenser 
  3. Receiver Dryer 
  4. Expansion Valve 
  5. Evaporator Coil 


The car Air Conditioning systems circulates the refrigerant under pressure through these five major components in a closed circuit. At these points in the system, the refrigerant undergoes preset pressure and temperature changes. Basically, the car Air Conditioner has two different circuits. One is for circulating the A/C refrigerant (cooling gas) while the other is for circulating the cabin air.


1. The Compressor of the Car Air Conditioner  

The refrigeration gas circulates within the closed Refrigeration Circuit. It enters the compressor which compresses it further. This increases both its temperature & pressure. the compressor draws the low -pressure refrigerant and increases its pressure. The compressor then forces it through the discharge valve (high side) into the condenser. The A/C compressor uses a magnetic clutch to connect and disconnect the compressor from the engine. The compressor then pushes the compressed gas to the condenser unit




2. Condensor

The consensor is located at the front of the vehicle. It sits behinds the front grill and in front of the car's radiator; facing the wind. Ambient air passing through the condenser removes the heat from the circulating refrigerant converts from gas to liquid. 




The Condenser units looks and works very similar to the engine radiator. It absorbs the heat from the hot refrigerant. Then, it converts the high-pressure gas into the high-pressure liquid refrigerant.


3. Receiver Dryer of the Car Air Conditioner 

The liquid refrigerant moves onto the Receiver Drier. It also contains a filter and a desiccant. Receiver Drier filters out the impurities and removes the moisture from the refrigerant. It also serves as a temporary storage tank for the liquid refrigerant.





4. Expansion Valve of the Car Air Conditioner 


The high-pressure liquid refrigerant then flows to the expansion valve. As the refrigerant passes through the valve it becomes low temperature, low-pressure liquid, and vapor. The expansion valve sprays the refrigerant into the evaporator in the mist form. This valve controls the amount of refrigerant entering the evaporator.



5. The evaporator of the Car Air Conditioner 


The low-pressure liquid immediately starts to boil and vaporizes as it enters the evaporator. A temperature sensor at the evaporator outlet controls the expansion valve. (If the outlet temperature is too high, it indicates that sufficient refrigerant is not reaching the evaporator. This will result in poor cooling of the cabin).




The temperature sensor sends the signal to open/close the expansion valve. This is to achieve the correct flow of the refrigerant. It enables the A/C to attain the rate and temperature of the evaporator outlet. The foggy mist of the refrigerant, then, enters the evaporator.


The Air-Flow Circuit 


On the other hand, the car occupants emit the heat which mixes with the cabin air. This warm air then enters the evaporator as the blower pushes it from the bottom side. The cabin air passing over the evaporator fins gives up its heat to the evaporating refrigerant. Since the refrigerant is colder than the air, it absorbs the heat from the air. This produces cool air which is then pushed into the cab interior. The ideal cabin air temperature for humans is around 23 degrees Celsius. Most automatic air conditioners try to achieve this by automatically shutting off/on the a/c compressor and recirculating the cabin air effectively.




The moisture in the air condenses upon entering the evaporator. It drops into the drain pan from which it is then drained out of the cabin. Evaporator removes humidity from the air and makes it dry. It passes the cooled air back into the cabin thru' the A/C vents provided in the dashboard. Then, the temperature and pressure of the refrigerant drops. It becomes low pressure & low-temperature gas. This low pressure and low-temperature gases again enter the compressor thru' the suction side and this cycle repeats.


Refrigerant used in the Car A/C


The refrigerant is a mixture of liquid that the Refrigeration Cycle uses. It undergoes the transformation phase from liquid to gas and back. The refrigerant is the fluid that is used in the car’s air conditioning system. The refrigerant transfers the heat as it changes from the liquid state to gas state. The scientists found that the Freon-R12 gas is the most damaging to the ozone layer. So, modern cars use R134a refrigerant which is environmentally friendly. The emission from the car air conditioners is the growing concern because of its impact on climate change.




Tips for using the Car A/C effectively 


  • Always keep the front grill clear of any obstructions for the proper functioning of the air conditioner.
  • A/C is most effective when all the windows are rolled up.
  • Keep the air conditioner in the recirculation mode when in use never mix with outer air to mix in the system.
  • Use the different modes according to the use.
  • To improve Fuel efficiency, Use the air-conditioner only when it is necessary.