Car Air-Conditioner: How It Works And Common Faults

We try to explain the workings of one of the basic features found in almost all cars now – An air-conditioner. This is something that can make its presence felt when it chooses to conk off on a hot summer day or a humid monsoon evening. As your car gets older, the car air-conditioner should be subjected to periodic maintenance. Let’s look how the system works and some commonly observed issues and possible solutions. A car air-conditioner works on the same principle as your room air-conditioner or a refrigerator. The fundamental principle involved is heat-exchange. A refrigerant gas (now commonly used is R134-a) that forces the transformation of liquid to gas and back to liquid, and in the process it absorbs or releases heat. Heat is absorbed when it expands (from liquid to gas form). The compressor of an AC, compresses the low-pressure gas into high-pressure, heating it up in the process. The condenser and the fan force this gas to cool down, turning it into a high-pressure liquid form, losing some of the heat in the process. This liquid high-pressure refrigerant flows through an expansion valve just before it enters the cabin, allowing it to expand, reducing pressure and further cooling it down.

The above mentioned cold liquid flows through the internal condenser or cooling coil, where it absorbs heat from the cabin as it evaporates into gaseous form. A blower motor pushes that cold air into the cabin, where it is compressed into a high-pressure gas and the cycle repeats itself. With the basic functioning of an AC dealt with, let’s get on with the commonly observed faults and possible remedies. How to check if there is no refrigerant gas in the system? Switch on your AC and if the blower motor is working, warm air is coming out, you hear the AC compressor clicking on and the condenser fan is working, but still, the car’s cabin is not cooling down, the suspect surely is the low AC refrigerant. A well-maintained car AC system can run for years with minor checks and top up of refrigerant every 2-3 years. If the gas has escaped, there is a leak somewhere in the system. It’s advised not to get it refilled before doing a complete test to eliminate the leakage. Look out areas include joints of the pipes and hoses that come from the condenser. Usually, a UV dye is fed into the system and checked with a UV light for leakage. The easier way of doing it though is simple soapy water, poured over the pipe and valves to check for leaks.

Moving to when the AC compressor is not coming on. Open the bonnet of the car, with the engine on and the AC off, you can observe that the belt that turns the AC compressor will continue to rotate and the outer part of the pulley will turn with it, but the center part of it will remain idle. This part is an electromagnetic clutch that operates the AC compressor and cycles it on and off. The same will start rotating the moment you turn on the AC. There is safety valve built into the compressor. First, if there is low refrigerant in the system the compressor will not turn on. Secondly, a fuse or a relay that powers the compressor could have malfunctioned. This is normally caused by water entering the system or faulty wiring. The third reason why the compressor is not firing up can be the compressor itself going bad. The same is normally characterized by symptoms like oil leaking out of it, abnormal squeaking and rattling noise coming out of the compressor. Replacing the compressor is a costly affair; make sure you check thoroughly to ensure that if indeed the compressor is at fault. To extend the life of your AC compressor, it is advised to get the system checked every 2-3 years, along with topping up of the refrigerant, add a few ml of compressor oil to keep it lubricated. If your used car is giving you frequent troubles, and you intend to sell it off, look no further than

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