The air conditioning system, simply put, removes heat from the air, and also reduces its level of humidity. Therefore, the air inside the car is always cooler and not as humid, which creates a feeling of freshness.
How is the microclimate created in the cabin?
A standard air conditioning system consists of several working units interconnected by a sealed tube system. It is filled with refrigerant, which changes from liquid to gaseous form and vice versa, transferring heat from the passenger compartment.
The most important detail on which the efficiency of the air conditioner depends is the control valve, which is installed on the evaporator located in the passenger compartment. The refrigerant in the form of a liquid under high pressure enters the evaporator through a control valve, where it is sprayed in the form of a gas-droplet mixture (fog). The control valve may be needle or diaphragm type. We will consider the first option.
Inside the needle valve there is a small hole, and the needle located in the hole is able to block it more or less, thus changing the effective cross section. The needle is driven by a temperature sensor placed inside the evaporator.
The liquid refrigerant, passing through a small hole in the valve, evaporates and turns into a gas under low pressure. This process is accompanied by a sharp drop in temperature. The smaller the hole, the colder the refrigerant becomes, that is, the temperature in the evaporator can be adjusted by inserting or withdrawing the needle from the hole. The surface temperature of the evaporator must be close to the freezing point of water, but not below it, otherwise ice will form on the evaporator, which will hinder the movement of air and heat transfer to the refrigerant.
As already mentioned, instead of a needle valve, sometimes a diaphragm is installed. There are no moving parts in it, so the flow of refrigerant to the evaporator is not regulated, but its supply is controlled by a thermostat or pressure switch. Having turned into a low pressure gas, the refrigerant passes through the evaporator (heat exchanger) and removes heat from the air in the cabin. For greater efficiency of this process, the heat exchanger is equipped with fins. The moisture contained in the air condenses on the outer surface of the heat exchanger and drains outside the passenger compartment. The air, having passed through the heat exchanger, returns to the cabin colder and drier.
The heat accumulated by the refrigerant must be transferred to the atmosphere, for which the refrigerant is sent to the condenser with the help of a compressor (this is another heat exchanger, usually located at the front of the car).
The compressor, whose task is to drive the refrigerant through the system pipes, transferring heat from a low temperature level to a higher one, works on the principle of a pump and is driven by a belt from the engine through an electromagnetic clutch so that the air conditioner can be turned off. When the compressor is running, it creates a vacuum that "sucks" gaseous refrigerant from the evaporator.
Inside the compressor, the pressure of the refrigerant rises, and it enters the condenser, but already in the form of a gas under high pressure. In the condenser, the gas turns back into a liquid, while the heat contained in it is dissipated from the surface of the condenser to the atmosphere.
From the condenser, the refrigerant - already in the form of a liquid under pressure - is again supplied to the control valve, and the cycle is repeated.
Additional "lotions"
In practice, the described basic scheme includes some more nodes, in particular, a receiver-drier, which is often (but not always) mounted between the condenser and the expansion valve. This device (he is sometimes called "accumulator") filters the refrigerant and removes moisture from it. Sometimes the dryer is equipped with a color indicator that shows when it is time to replace it (this means that he has gained maximum moisture). into the tubing system (between condenser and evaporator) sometimes a sight glass is built in, and then you can observe the state of the refrigerant (the presence of unnecessary bubbles, etc.).
The air conditioning system also includes a blower that drives air through the evaporator, and a fan with a thermostat that increases the efficiency of the condenser. Typically, the system also includes a pressure sensor with a switch. It is located next to the receiver-drier and controls the operation of the compressor and condenser fan, as well as maintains optimal pressure in the system (different for different systems).
In most systems, a heating element is also attached above the evaporator. Air flow using "mixing damper" distributed between the evaporator and the heater so as to give it the desired temperature.
And what about the environment?
Until recently, R12 freon was used in car air conditioners. Then it was found that the chlorofluorocarbons contained in it have a detrimental effect on the ozone layer, so now it is forbidden to release R12 into the atmosphere. In addition, when exposed to an open flame, R12 releases the deadly gas phosgene. It is still allowed to fill with them air conditioners of previous releases, as is the operation of these air conditioners.
Accordingly, the price of R12 freon increases by 5–10% per month. Eventually she will become "recharge" old systems will become simply ruinous. Already now freon R12 costs $150 per kilogram in the West, and two years ago it cost $65. Modern systems use more "eco-friendly" refrigerant - R134A.
Systems rated for R134A are designed to be leak-free during maintenance and repair. For this, special valves and other devices are installed in the right places.
Theoretically, R134A can also be uploaded to an old air conditioner by making the appropriate changes. However, this refrigerant is 15 percent less efficient than R12, so the old type of air conditioner will work worse with it. In addition, there is another problem: R134A refrigerant leaks, albeit weakly, through hoses made of pure rubber. This substance requires special hoses with an internal nylon braid. At the same time, in older systems, so-called "completed" connecting fittings that are able to break through this braid. In a word, at the moment it is more profitable to use the old refrigerant.
In fact, there are so-called "substitution" refrigerants designed to replace R12 and do not require an expensive reworking of the system to R134A, but, as experts say, they cannot be let into the air conditioner even for a cannon shot. Some of these substances contain butane, which can ignite inside the system and destroy test equipment.
If you want to switch from R12 to R134A, then it is best to change the oil along with the refrigerant (mineral to synthetic) in the system, install a new receiver-drier, change the rubber hoses and check the operation of all components. Then there is hope that the system will work satisfactorily.
To make everything work
In order for the air conditioning system to work well, you need to be able to handle it. For example, many do not know that the air conditioner will only work effectively when all the windows in the car are closed, as well as the sunroof. To cool the interior faster on a very hot day, you need to open all the doors for a minute or two, and when the car is blown, close everything and turn on the air conditioner (with the engine running).
The drying effect of the air conditioner reduces fogging of the windshield and side windows of the passenger compartment, so sometimes it is useful to turn on the air conditioner at the same time as the stove. True, some climate systems do not provide for the simultaneous operation of the air conditioner and the stove.
The air conditioning system contains oil that circulates with the refrigerant. If the system is left idle for a long time, some of its parts, in particular, neoprene gaskets, dry out and collapse, giving a leak. Therefore, it is advisable to turn on the air conditioner once a week for at least ten minutes, including in winter, so that the oil lubricates all components of the system.
What can be fixed?
Air conditioners are not subject to "home", amateur repair. The refrigerant is a capricious substance, professional equipment is required for its complete pumping out and injection of a new one, and in order to ensure complete tightness, special highly sensitive leak detection devices are needed.
If the air conditioner is broken, then at least some parts need to be replaced, including special pipes and fittings, but there are many of their sizes. And for fastening tubes to fittings, special crimping devices are used.
So, if you have problems with the air conditioner, rely only on specialists. Contact companies that make complex repairs, and not just pump the volatilized refrigerant. If the refrigerant "gone" out of the system, then you first need to find the cause, otherwise the new refrigerant will evaporate in the same way!
Similarly, if your compressor is stuck, then just replacing it is not enough: in a few months it will jam again. You must first remove chips and other debris from the system, and then flush it with a special solution or nitrogen. You will also have to replace the receiver-dryer (shavings left in it) and add fresh refrigerant.
Most often, the capacitor is damaged. It is located in front of the car radiator and is protected only by the radiator grille.
The second problem is needle valve failure (he's covered in mud). When cleaning the valve, it is necessary to remove dirt from it, and not to push it inside!
There are other problems - for example, the compressor is noisy. Usually, this speaks of his near end.
It is easy to check the condition of the drive belt. In some machines, the compressor is driven by a separate belt. This is a good option. However, modern cars are often equipped with long "multifunctional" a belt that drives several devices at once, often including a water pump. So, if the A/C compressor drive pulley bearing suddenly seizes, you won't go anywhere until you find a smaller belt to "get around" compressor!
Other aspects
If the refrigerant does leak through the rubber hoses, then replacing them is quite problematic, since it is difficult to reliably seal the new hoses on the old aluminum fittings.
Be aware that the air conditioner may not turn on if the ambient temperature is lower than the set temperature or if the pressure in the system is much lower (refrigerant leak) or more than optimal.
An excess of oil, refrigerant, air or moisture entering the system, severe contamination of the condenser or evaporator fins, and a malfunction of the car’s cooling system also lead to malfunctions in the air conditioner (overheat), as well as compressor clutch slippage.