How it Works, Basically
Any system that lowers temperature operates in similar fashion. First you take a gas, like Freon, and place it in a sealed system. This freon is then pressurized using a compressor. As it's pressurized, it gets hot by absorbing the heat around it. This hot gas is then circulated through a series of tubes that dissipate the heat. Scientifically, the gas removes heat rather than adds cold, but that's a lesson in physics that doesn't really matter to us right now. The gas can lose lots of its heat, in other words it gets really cold, when you reduce the pressure. As it cools it becomes a liquid. This is when you get cold air blowing on your sweaty forehead.
To use this system in a car, it needed very little adaptation from its early applications as a refrigeration device. since it was discovered that Freon (R-12) was harmful to the earth's Ozone layer, it's been phased out for automotive use, and replaced with the slightly less efficient, but harmless R-134a refrigerant. This is actually good news because for years it was against the law to service your own air conditioning system without a license. Now that the refrigerant is safer, we can all work on our own A/C systems again! Some cars have not been converted from the old R12 to R-134a, but this conversion can be done easily.
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Compressor:
This is the heart of your a/c system. The compressor is what takes the refrigerant (the gas) and pressurizes it so it will cool the air. It's run by an engine belt. The compressor also has an electrically operated clutch that turns the compressor on and off as you demand more cool air.
Condenser:
The condenser is like a miniature radiator, usually mounted at the front of the car right next to your big radiator. Sometimes the condenser will have its own electric cooling fan, too. The hot, compressed air passes through the condenser and gets lots cooler. As it cools, it becomes a liquid.
Evaporator:
The evaporator is another little radiator that does just the opposite task as the condenser. As the super-cool liquid is passed through its tubes, air is forced through and gets really cold, right before it hits your face. As it warms up again, the refrigerant starts turning back into a gas.
Thermal Expansion Valve:
You don't always want to freeze your toes off, so the a/c system has a valve that controls the flow of super-cool refrigerant to the evaporator. This way you can regulate how cold the air blowing on you gets. There are a few types of valves in use these days, but they all do the same thing.
Drier or Accumulator:
The drier, also known as the receiver-drier, is sort of the safety catch for your system. The compressor is only supposed to compress the gas form of your refrigerant. However, there's always a chance that some liquid could make it back that far. The drier catches this liquid before it can damage your compressor. Since even the tiniest leak or careless installation can introduce water moisture to the system, the drier absorbs this chemically, using what's called a dessicant (similar to that packet of "DO NOT EAT" that comes with electronics). The drier also has a filter that catches any gunk that might be in there.
You may need to recharge your system if your car doesn't feel cold enough
If your car doesn't feel as cold as it used to, then yoursystem may need servicing, as the refrigerant gas that is used to operate the system depletes over time. Most vehicles lose up to 15% per year on average. This leakage usually occurs because the system is not used during the winter months, allowing the small "O" ring seals to dry out and causing a gradual deterioration in system performance. If this continues, eventually the system will not be able to operate at all.
Most problems of this type can be corrected fairly easily by a leak check of your system followed by a complete refill of your air conditioning refrigerant. This is sometimes referred to as a re-gas.
Consider running your air conditioning year round to help maintain the system
If you run the air conditioning in the winter it will help to keep the system well lubricated and leak tight. This is because the refrigerant actually carries the oil that lubricates the system and most importantly the compressor. It also keeps the seals and hoses moist, thus preventing them from drying out and cracking, which can lead to leaks.
Strange noises should be attended to immediately
If your air conditioning system suddenly starts making noises you have not heard before it is important to have a qualified vehicle air conditioning specialist have a look at it. Some noises could be early symptoms of a compressor failure (the compressor is the air conditioning pump). The compressor is usually the most expensive part of the system and if the bearings in your compressor break down or if the compressor seizes up it also means that other components can become contaminated. A flush of the system would then be needed, as well as replacement of the compressor and other parts, which could be quite costly.
Don't worry about a pool of water forming under your car after using the A/C
If you do find a puddle of water on the ground, usually under the passenger area, don't be surprised. This is a normal feature of the system; it is only water dripping from the air conditioning evaporator. The evaporator has a drain tube fitted to allow the condensation from the evaporator to drain away from the vehicle.
Excessive moisture inside the car can be fixed easily
Sometimes the drain tube from the evaporator may become blocked or detached allowing the condensation to build up inside your evaporator. If this occurs, water will just build up inside your car to a point where there are damp carpets or high humidity type problems. These problems can be solved with low-cost servicing. Talk to your mechanic if you notice a lot of moisture in the car.
Have your air conditioning serviced regularly, even if there are no visible problems
Just as the other systems of your car need servicing on a regular basis, the same is true for the air conditioning system. The compressor needs oil, or else it will seize up. The filter collects debris and moisture. If the filter becomes blocked, then the performance of the system will deteriorate and it can even quit working entirely.
Normally the refrigerant gas in a car air conditioning system has to be recharged completely within four years from the manufacture's date and every two to three years after that.
Although your car's air conditioning system is not usually part of the regular maintenance schedule, it's a good idea to have your mechanic do an annual servicing to guard against malfunctions in the compressor and other vital parts of the system. Regular maintenance will save you money in the long run and guarantee you comfort in the hottest months.
