* The history of automotive air conditioning compressor *
* Pressure regulating devices
* Parts of an automotive air conditioning system
* Orifice tube
* Thermal Expansion Valve
In this paper we give a brief explanation of automotive air conditioning, starting with its evolution, since man realized inside your new machine, the car, it was very hot and uncomfortable, and decided I should do something thereon, to the present day, where air conditioners are basic choice of any car. A definition is then given of the basic parts of different air-conditioning systems, and finally, discuss the system working fluid, the coolant.
1. The history of automotive air conditioning
The first cars were not exactly comfortable, its thin tires and interior mats provided a very uncomfortable ride. In the winter the passengers entertained, and in summer the air conditioning was the result of the breeze blowing when traveling at 15 mph. Nothing is hotter than the inside of a car, so when automakers began to shut down the booths, it was obvious that they had to do something with this heat, at first placed openings in the floor, but this brought more dust and dirty air conditioning.
In 1884 William Whiteley had the great idea of putting ice cubes in a container under the cab of the carriages and blowing air in through a fan attached to the shaft. A bucket near floor openings was equivalent in the car, then came one evaporative cooling system called Wheater Eye (Eye climate), which produced an effect of lowering the temperature by passing air over water . This system is still available in the VAN and RV. This system was invented by a company called Nash.
The first car with a cooling system like the present was the Packard 1939, in which a spiral chiller, which was nothing more than a very long evaporator that wrapped around the cabin, and whose control system was the fan switch.
Then came Cadillac, which produced 300 cars with air conditioning in 1941. These early air conditioning systems have a great disadvantage, there was a clutch on the compressor, so it was always on while car was running, and turn off the system, you had to stop the car, leave it, open the hood and remove the compressor belt. It was not until after WWII that Cadillac promoted a new feature: air conditioning controls. These controls were located in the back seat, so the driver had to stretch to the back seat to shut down, but it was still better than turning off the car and disconnect the compressor belt.
The air conditioners were for many years a very common option. It was not until 1966 that the Seviche Manual Motor reported that it had sold 3.56 million air conditioning units for cars car sales with the option of air conditioning soared. By 1987 the number of air conditioning units sold was 19,571,000. It is currently estimated that 80% of cars and light trucks in use have air conditioning units.
Increased air conditioning units installed on cars in the 70s and 80s was because the late 70s, in the United States began moving people did warmest states. Then people who bought cars they wanted were fitted with all available options. The sellers made more money with these extra options, so they began to include air conditioning as a basic feature and not an option, despite being one of the most expensive. Over time air conditioning units were improving, so that drivers do not have to worry about the heat passing because their air conditioning units were not working well.
Today, air conditioning units are very efficient, with modern systems such as ATC (Automatic Temperature Control, for its acronym in English), which is more reliable than the old thermostats. The onboard computer also ensure that both driver and passengers feel comfortable.
The automotive air conditioning units are continuously evolving, there are more designs of compressors and new electronics that improve the efficiencies of these teams, and not just the components are evolving from refrigerants, CFCs (chlorofluorocarbons, also known as or Freon R-12) are being replaced by other refrigerants such as R-134, which contains no chlorine, which are due to contaminants, particularly harmful for the ozone layer.
2. Parts of an automotive air conditioning system
Most existing vehicles have three different types of air conditioning systems, but the design and layout of these types are very similar. The most common components of these systems are:
Commonly called the heart of the system, as the name implies, the gaseous refrigerant taking for this engine power flows through transmission. The air conditioning systems are divided into two sides, the high pressure side and the low side pressure, also called suction and discharge respectively. The compressor inlet gas outlet of the refrigerant evaporator outlet, and in some cases makes the accumulator, compressed and sent to the condenser where the heat transfer occurs inside the vehicle absorbed.
Here is where the heat dissipation. The capacitor has a great resemblance to the radiator because both serve the same function. The capacitor is designed to dissipate heat, and is normally located in front of the radiator, but sometimes, due to the aerodynamic design of the vehicle body, is placed in another place. The capacitor should have good air flow anytime the system is running. Within the condenser, the refrigerant gas from the compressor, which is heated, cooled, during cooling, the gas condenses to become a high pressure liquid.
The evaporator is located inside the vehicle, and serves to both heat absorbing excess moisture therein. In the evaporator the hot air passes through the aluminum fins joined to the tubes, and the excess moisture is condensed therein, and the dirt and dust adheres air leads in turn to the wetted surface of the fins, then the water is drained to the outside.
The ideal temperature of the evaporator is 0 C (32 F). The refrigerant enters the bottom of the evaporator as a liquid at low pressure. The hot air passing through the fins of the evaporator causes the refrigerant within the evaporating tubes (the refrigerant having a low boiling point). In the evaporation process the refrigerant absorbs large amounts of heat, which is carried by the refrigerant out of the vehicle interior. There are other components of air conditioning systems that work together with the evaporator, since they must be controls to maintain the low pressure and temperature, since if it falls below the above value, the product of the condensation water excess moisture not only condense but freezes about the evaporator tubes, and this decreases the efficiency of heat transfer therein.
2.4. Pressure regulating devices
The temperature of the evaporator can be controlled by regulating the flow and pressure of the refrigerant within it. There are many devices created for this purpose are presented below which most commonly are:
Orifice tube: It is probably the most used device for regulating the pressure, and is the most widely used in Ford vehicles and GM. Is located inside the inlet tube evaporator or in the fluid line, somewhere between the condenser and the evaporator inlet. To know the exact location of this device, just tap the liquid line and locate the point where the temperature goes from hot to cold.
Thermal expansion valve: Another common pressure regulator is the thermal expansion valve, or TXV. This type of valve measures both temperature and pressure is very efficient and regulating the flow of refrigerant entering the evaporator. Various types of TXV but, despite being very efficient, have certain disadvantages with respect to the orifice tube system, as well as the tube orifice can clog with impurities of the refrigerant, but also possess small moving parts can jam and have a malfunction due to corrosion.
2.5. Deposit – dryer
The reservoir – the dryer is used in high pressure side of the system utilizing a thermal expansion valve. This type of valve requires coolant, and to be sure that only enter said valve, the tank is used – dryer, which separates the gas and liquid, while eliminating the moisture and impurities filtered. Normally the tank – has a glass dryer level, at the top, which is used to recharge the system, in normal conditions, the vapor bubbles should not be visible through the sight glass.
The accumulators are typically used in systems using orifice tube and connected to the outlet of the evaporator, where it stores excess fluid not evaporated, because if this fluid passes to the compressor could damage it, although this is its primary function, the accumulator also serves to remove moisture and impurities.
Previously automotive air conditioning systems used as the working fluid called a refrigerant chlorofluorocarbon-12 (CFC-12 or known commercially, Freon), but studies have found that the CFC-12 damages the ozone layer, so that discontinued in 1995, although there are still large inventories of said refrigerant being used until exhausted existence apart that recycling of the same claims that remain available for a while.
To replace CFC-12 used the R-134, which is the only alternative refrigerant that has been tested and recommended by the automakers, also accepted by the EPA (U.S. Agency for environmental protection, for short English), and it is used in all cars manufactured after 1995.
There are other alternative refrigerants in the market, as the GHG-X4, a mixture of the following refrigerants: R-22, R-142b, R-124 and a small amount (around 4%) of R-600 (Isobutane). This s the refrigerant used as a substitute for converting existing equipment air conditioning in old cars, to replace the R-12. The isobutane present in the GHG-X4 helps the lubricating oil entrained in the refrigerant returning to the compressor, so there is no need oil changes, and isobutane is in such small proportions that the refrigerant becomes flammable, so there is no danger of explosion.
To carry out this work we used information from the following websites:
Information about the authors
This work was done by Diego Medina, Rafael Suarez, Raul Silva and Jorge Matos, who are students in the last semester of Mechanical Engineering at the east coast of Lake Core of the University of Zulia, located in Cabimas, Zulia State, Venezuela .
This activity is located within the area of technology, and the suggested title is “The automotive air conditioning”
Cabimas, May 2000