How does an air conditioner work, and what to do if it breaks down? (Mazda Capella GE)

Once the preserve of luxury cars, air conditioning is now becoming an integral part of more and more "regular" family cars. Experts estimate that by the beginning of the next century, half of all European cars will be sold with air conditioning as a standard accessory.

The air conditioning system, simply put, takes heat from the air and also reduces its humidity level. Therefore, the air inside the car is always cooler and less humid, which creates a feeling of freshness.

How is the microclimate in the cabin created?

A standard air conditioning system consists of several working units connected to each other by a sealed system of tubes. It is filled with a refrigerant that changes from liquid to gaseous form and back, transferring heat from the cabin.

The most important part on which the efficiency of the air conditioner depends is the control valve, which is installed on the evaporator located in the car's interior. The refrigerant, a liquid under high pressure, enters the evaporator through the expansion valve, where it is sprayed as a gas-droplet mixture (mist). The expansion valve can be either a needle valve or a diaphragm valve. 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 close 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 passes 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, meaning the temperature in the evaporator can be adjusted by moving the needle in or out of 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 the transfer of heat to the refrigerant.

As already mentioned, a diaphragm is sometimes installed instead of a needle valve. It has no moving parts, so the flow of refrigerant into the evaporator is not regulated, but its supply is controlled using a thermostat or pressure switch. Having turned into a low-pressure gas, the refrigerant passes through the evaporator (heat exchanger) and takes heat from the air in the cabin. To make this process more efficient, 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 cabin. The air, having passed through the heat exchanger, returns to the cabin colder and drier.

The heat accumulated by the refrigerant must be released into the atmosphere, for which the refrigerant is directed to the condenser using a compressor (this is another heat exchanger, usually located at the front of the car).

The compressor, whose job it is to pump the refrigerant through the system's tubes, transferring heat from a low temperature level to a higher one, operates 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 operates, it creates a vacuum that "sucks" the refrigerant gas out of the evaporator.



Inside the compressor, the refrigerant pressure increases 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, and the heat contained in it is dissipated from the surface of the condenser into the atmosphere.

From the condenser, the refrigerant – now in the form of a liquid under pressure – is again fed to the expansion valve, and the cycle repeats.

Additional "bells and whistles"

In practice, the basic circuit described includes some more units, in particular, a receiver-dryer, which is often (but not always) mounted between the condenser and the expansion valve. This device (sometimes called an "accumulator") filters the refrigerant and removes moisture from it. Sometimes the dehumidifier is equipped with a color indicator that shows when it is time to replace it (this means that it has absorbed maximum moisture). Into the tube system (between the condenser and the evaporator) sometimes a sight glass is installed, and then the state of the refrigerant can be observed (presence of unnecessary bubbles, etc.).

The air conditioning system also includes a blower, which forces air through the evaporator, and a fan with a thermostat, which 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, and also maintains optimal pressure in the system (different for different systems).



In most systems, a heating element is also mounted above the evaporator. The air flow is distributed between the evaporator and the heater using a "mixing damper" to give it the desired temperature.

What about the environment?

Until recently, R12 refrigerant was used in automobile air conditioners. It was later discovered that the chlorofluorocarbons it contained had a detrimental effect on the ozone layer, so releasing R12 into the atmosphere is now prohibited. In addition, when exposed to an open flame, R12 releases deadly phosgene gas. It is still permitted to fill air conditioners of previous releases with it, as is the operation of these air conditioners.

Accordingly, the price of R12 refrigerant is increasing by 5-10% per month. Eventually, it will reach a level where recharging old systems will become simply prohibitive. R12 freon already costs $150 per kilogram in the West, down from $65 two years ago. Modern systems use a more environmentally friendly refrigerant, R134A.

Systems designed for R134A are designed to be leak-free during maintenance and repair. For this purpose, special valves and other devices are installed in the required places.

Theoretically, R134A can be pumped into an old air conditioner, with appropriate modifications. However, this refrigerant is 15 percent less efficient than R12, so an older type air conditioner will perform 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, older systems use so-called "barbed" connecting fittings, which are capable of breaking this braid. In short, at the moment it is more profitable to use the old refrigerant.



In fact, there are so-called "replacement" refrigerants designed to replace R12 and do not require expensive system modifications to R134A, but, as experts say, they should not be allowed anywhere near an air conditioner. Some of these substances contain butane, which can ignite inside the system and will also damage test equipment.

If you want to switch from R12 to R134A, it is best to change the oil along with the refrigerant (mineral to synthetic) in the system, install a new receiver-dryer, 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 know how to use it. For example, many people don't know that the air conditioner will only work effectively when all the windows in the car, including the sunroof, are closed. 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 gets a chill, close everything and turn on the air conditioning (with the engine running).

The drying effect of the air conditioner reduces fogging of the windshield and side windows, so sometimes it is useful to turn on the air conditioner at the same time as the heater. However, some climate control systems do not allow for the simultaneous operation of the air conditioner and heater.

The air conditioning system contains oil that circulates along with the refrigerant. If the system is left idle for a long time, some of its parts, in particular the neoprene gaskets, dry out and deteriorate, causing leaks. 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 system components.

What can be fixed?

Air conditioners are not subject to "home" or amateur repair. Refrigerant is a capricious substance; professional equipment is required to completely extract it and refill it, and specialized, highly sensitive leak detection devices are needed to ensure a complete seal.

If the air conditioner breaks down, then at least some parts need to be replaced, including special tubes and fittings, but there are many standard sizes of them. And to attach the tubes to the fittings, special crimping devices are used.

So, if you have problems with your air conditioner, rely only on professionals. Contact companies that perform complex repairs, and not just pump in leaked refrigerant. If the refrigerant has "left" the system, you must first find the cause, otherwise the new refrigerant will evaporate in the same way!

Similarly, if your compressor is jammed, simply replacing it is not enough: in a few months it will jam again. You must first remove shavings and other debris from the system, and then flush it with a special solution or nitrogen. The receiver-drier will also need to be replaced (there were shavings left in it) and pump in 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 the failure of the needle valve (it gets clogged with dirt). When cleaning a valve, you need to remove dirt from it, not push it inside!

Other problems arise, for example, the compressor makes noise. Usually, this indicates that his end is near.



It's 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 a long "multi-functional" belt that drives several devices at once, often including the 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 "bypass" the compressor!

Other aspects

If refrigerant does leak through the rubber hoses, replacing them can be quite challenging, as it is difficult to reliably seal new hoses onto old aluminum fittings.

Please note that the air conditioner may not turn on if the ambient temperature is below the set temperature or if the pressure in the system is much lower (refrigerant leak) or higher than optimal.

Air conditioning malfunctions can also be caused by excess oil, refrigerant, air or moisture entering the system, heavy contamination of the condenser or evaporator fins, a malfunction of the vehicle's cooling system (overheating), or compressor clutch slippage.