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The air conditioner in the car: history, operation and advice

With the onset of summer and the hot weather, we tend to turn on our air conditioner directly. But do you know what are the risks and the precautions to be taken before that?

We tell you everything you need to know about it and how to use it, but first, let's start with a little history.

The history of air conditioning in the automobile

The history of air conditioning in general, dates back to 1875 to know its first beginnings. But, its official history begins in 1906 with the patent submitted by Willis Carrier, its use was intended primarily for buildings. For vehicles, it was not until 1933 that a company in New York offered the installation of air conditioners on vehicles, and like all new products, they were expensive and intended primarily for luxury vehicles.

Six years later, in 1939, the American automaker Packard Motor Car Company offered air conditioning as an option on its vehicles at the then price of $ 274 (or $ 4,800 today). A system not very efficient because it had no control button to turn it on or off, and not even to adjust the temperature. The system fed by an additional belt connected to the engine, collected air from the rear of the vehicle to take it to the front, not enough to satisfy the first customers.

It was not until 1953 that Chrysler offered standard air conditioning on its luxury model: the Imperial. Its system is more efficient and uses the Airtemp system developed by Chrysler. In 40, Cadillac is not in line with Chrysler and also offers air conditioning on these vehicles, but with its own design which was however cumbersome since located under the passenger seat, it is deactivated by removing the belt. The system is subsequently developed, in particular thanks to Frederick Jones, a mechanic and inventor, who obtained more than 40 refrigeration patents for air conditioning. In July 1940 he obtained a patent for a cooling device mounted on the roof of a truck. Soon after, the invention was produced for refrigerated trucks that carried flash-frozen foods, which was an invention of Clarence Birdseye. Nash Motors Corporation was the first manufacturer of an integrated ventilation, heating and air conditioning system. It boasted of being compact in style and affordable at $ 345. The controls have been integrated into the dashboard, a big step forward for the comfort of the pilot. Air conditioning is therefore democratized in the USA, in 1969, 50% of vehicles sold were equipped with air conditioning. Elsewhere in the world, air conditioning is gradually being answered depending on the country, the USA was at the forefront of the automotive world.

His utility

Automotive air conditioning is a system that cools and sanitizes the interior of an automobile when the outside temperature, or humidity, is higher than desired inside. The air conditioning is coupled with a ventilation and heating system.

Components and operation

The air conditioning system has undergone a lot of evolution since its creation. However, nowadays air conditioning systems work for most of the same principles, there are performance and comfort options that we will not develop here, we focus on the basics of its operation.

The main components of the air conditioning circuit:

Compressor driven by the car engine.


Desiccant filter.



To understand how all these elements work together, it is first necessary to know that the physical principle used is that of the compression / decompression of a gas. When it is compressed: the temperature then rises / When it is relaxed (the reverse of compression therefore): it cools down. In the case of air conditioning, we will take advantage of this phenomenon to obtain cold. Unfortunately, to have cold you must first generate heat (by compression), so let's see how the inventors found a solution to keep only the cold. The aim is then to be able to expand pressurized gas in order to obtain fresh air. However, how do you get this gas under pressure? Quite simply thanks to a compressor which is powered by the accessory belt (therefore by the movement of the motor via the Damper pulley, hence greater consumption when using the air conditioning. It is indeed necessary to run the compressor, which requires more effort from the engine.) Unfortunately, the compressor will raise the temperature of the gas by compressing it, so expanding it will only give a lukewarm temperature ... The technique therefore consists of cooling this pressurized gas before it is released. relax, so you can get a much more "intense" cold. For this, we do as with engine water, we pass the gas under pressure in a cooling radiator.

In summary :

I compress a gas (thanks to a compressor) which then begins to heat. Until then we have hot, the opposite of what we want ... But let's wait!

I cool the latter, it then turns into liquid. The gas therefore became liquid and above all, its temperature was reduced (while keeping its pressure).

This liquefied gas is expanded to obtain cold because: expanded / depressurized gas = creation of cold = basic physical principle.

Now that the cold is obtained, it suffices to pass the hot air from the outside to the place where the cold is channeled, ie into the evaporator which then becomes a kind of "active radiator" since cooler than the surrounding air.

Gas enters the compressor

The compressor compresses it with the energy of the motor, resulting in a slight overconsumption. We then enter the part of the circuit known as high pressure (generally between 15 and 20 bars).

The compressed gas arrives in the condenser to be cooled, which liquefies it at the same time (it is always under high pressure). Hence its name condenser for condensation.

The dehydrator takes care of removing any water in the gas in order to preserve the system. In addition, there is a filtering of impurities from the liquefied gas. Any improper gas could harm the entire circuit.

The "regulator" expands the gas which lowers its pressure and generates cold (more or less intense depending on the degree of decompression). We then enter the part of the circuit known as low pressure (less than 5 bars).

The cooled gas passes through the evaporator which looks like a radiator.

The outside air (supplied by a duct drawn in light gray) passes into the evaporator, which cools it.

The evaporator catches much of the moisture (and dust) from the incoming air and releases it as water under the vehicle. So you don't have to worry about seeing water running under your car in the middle of summer.

Advice and interviews

Before starting the hot season, it is recommended to change your cabin filter every 20,000 km and / or every year, and to check the condition of the various components of the air conditioning system by a qualified professional.

In the same vein, it is necessary to monitor the level of gas and to recharge it in the event that it should run out, but before it is necessary to check the cause of the gas leak and repair it, it should be known that the gas can be harmful for the gas. environment in it is released into the air.

It is also necessary to maintain the ventilation pipes by carrying out an antibacterial treatment every year.

It is generally recommended not to attempt to maintain an ideal temperature of 21 degrees in hot weather. The rule is easy to remember: no more than 4 to 5 ° C difference from the outside temperature. If the outside temperature is very high and you want to have a pleasant temperature, in this case, gradually decrease or increase the temperature until reaching the desired temperature in order to avoid thermal shocks. In other words, when the outdoor thermometer reaches 30 ° C, do not turn the air conditioning dial above 25 ° C. If in the case (for example) the outside temperature is 40 degrees, lower it to 35, then 30, then 25 degrees. On the one hand, the body does not appreciate high amplitude thermal shocks, on the other hand the mucous membranes will suffer less from drying out.

Another very effective tip is to direct the air flow to the forearms and parts of the body exposed to sunlight rather than to the face. First of all, be patient! It takes time to cool a passenger compartment that has been exposed to sunlight for a long time, especially in a minivan fitted with a glass roof. Start by ventilating well before switching on the air conditioning: driving with all the windows down for a few minutes will allow the upholstery to be cooled and will help the passengers to wait until the "cold" arrives. Then, select the "Auto" mode and a set temperature only 5 ° C lower than that displayed by the outdoor thermometer.

If so many people are obsessed with air conditioning and its effects (itchy eyes and throat, sneezing), it is mainly because they persist in setting it "too cold". Some very high-end vehicles, however, attempt to correct these inconveniences by combining the air conditioner with air purification and humidification systems.

Use the recycle function when driving in a tunnel.

Turn off the air conditioner a quarter of an hour before you reach your destination to let the evaporator dry completely, which will reduce the risk of bacteria and fungus growth.

When a vehicle is exposed to direct sunlight, especially during heatwave periods, the materials used in the passenger compartment's upholstery can emit toxic fumes, hence the need to renew the air by opening the windows before using it. air conditioning with the windows closed.

There is a question that comes up frequently among motorists concerned about economy and ecology: is it better to drive with the windows open or the air conditioning on? The answer is provided by the results of studies published by The National Renewable Energy Laboratories corroborated by the tests of the manufacturers themselves: moderate use of the air conditioner consumes less fuel than driving with the windows down. We still need to agree on the definition of the term "moderate".

Prefer solar films on your windows. This saves a few degrees inside the cockpit and therefore possibly avoids the air conditioning.

If you've parked your car outside in direct sunlight and need to be on the road, you'll tend to turn on the air conditioning. However, if you turn on your air conditioning right away, that is exactly when you will consume the most! The engine will have just started and the air conditioning will have a hard time cooling the hot passenger compartment. This inevitably leads to overconsumption of more than 30%! We therefore recommend that you open the windows wide at the start of your journey and then switch to the air conditioning when the interior has cooled down a bit.

Advantages and disadvantages

Air conditioning in the car has many advantages, in terms of comfort and safety. Thus, it limits the risk of heat-related drowsiness, and the air is generally cleaner, because the filters block fine particles and allergens such as pollen.

It is estimated at 1L of fuel per 100 km (about 5%) consumed by the compressor and therefore by the air conditioning.

Refrigerant gases produce a big greenhouse effect and some of it can always escape in transport, repairs, etc.

Environmental impacts

According to the French agency ADEME, air conditioning increases fuel consumption, as well as greenhouse gas emissions, especially during accidents, vehicle fires or refrigerant leaks:

In city driving, an average vehicle consumes 31% more gasoline (or 35% more diesel for diesel vehicles);

On the road, consumption increases by around 16% for gasoline vehicles and 20% for Diesel;

Over the year, all seasons combined, "air-conditioned vehicles consume on average 5% more fuel than those which do not";

An increase in pollutant emissions (CO and NOx) is observed for gasoline engines, and of NOx and particulate matter (PM) for diesel engines;

An increase in CO2 emissions, which contributes to global warming of around 6 to 10% for an average vehicle, mainly due to the releases into the atmosphere of refrigerant, at the end of the vehicle's life or during maintenance operations;

Even when it is not working, an air conditioning system loses refrigerant (R134a) (leaks, maintenance, servicing, accidents, fires, non-recovery at the end of the vehicle's life, etc.), and this gas has a very powerful heating effect , 1,300 times more powerful than CO2. Thus, an average vehicle increases its annual greenhouse gas emissions by 10 to 15% when it is air conditioned. On the test bench, it is the hoses and fittings that show the greatest source of refrigerant gas leaks, with differences of 1 to 9 on four hoses studied and of 1 to 20 on several fittings. Even new compounds gave rise to leaks of 1 to 20 g / year of refrigerant gas. The compressors tested also lost 0.2 (new) to 5 g of fluid (compressor having been in operation for six months) per year10. The complete system (2003 data) commonly exhibited leakage rates of 10 to 70 g / year. ADEME estimated that technical improvements at the pace of the 2000s will still leak 10% of the fluid each year in 2010, an impact for the fleet of French cars equivalent to that of an emission of 2 Mt of CO2 equivalent. in 2005, including 100 kt due to the failure to recover the fluid at the end of the vehicle's life or the air conditioning system. A prospective assessment published in 2003 was 3.6 Mt of CO2 including 1.6 for end-of-life non-recovery in 202010;

Type of gas: R134a refrigerant replaced R12 refrigerant according to the Montreal Protocol (the international agreement for the protection of the stratospheric ozone layer). In a few years, HCFC R22 will follow the same path.

As the air conditioner does not produce water, there is therefore no risk of Legionella.


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