This is the compressor, the heart of the air conditioning system. As you can see, it looks like two cylinders. The cylinder 
on the right is a liquid receiver, while the “cylinder” on the left is the compressor.

This is a rotary compressor, the entire system is sealed up and compressor oil is poured into the compressor to lubricate the moving parts. The compressor operates at enormous pressure and subjected to very high temperature. It is very challenging to lubricate the moving parts in such a hostile environment, especially when the oil needs to co-exist with the refrigerant. The compressor oil is not any other oil that you pour into the car engine, it is a lot more demanding.

How reliable your compressor will be, is largely determined by how well the compressor oil copes under such a demanding condition. Because, it will be labour intensive to replace the compressor oil,  people seldom do so; you might as well replace the compressor. When the oil loses its lubricating properties, it is time the compressor fails. When the 
compressor oil turns acidic, it may corrode the copper enamelled wiring, causing an short circuit which trips your main circuit breaker. You may like to read up on Aircon Power Trip.

Compressors are built to last, or else manufacturers wouldn’t be giving you a 5 years warranty. What that causes 
compressor premature failure is often a result of technician mishandling the gas system.

Always avoid fully dismantling the air conditioner for chemical cleaning; avoid contaminating the gas system. Do not top 
up gas unnecessarily.

Air conditioning works by compressing the gas so much that it turns into a liquid (the compression ratio is more than 600 times), in the process, heat is created which is dissipated using the large condenser fan. The opposite happens when the liquefied gas evaporates back into a GAS; this is the fundamental concept of how air conditioning works.

As you can see from this picture above. Inside the cooling ” fan coil” are the copper pipes. It is inside these copper pipes that the liquefied gas evaporates. The cooling “fan coil” is made of aluminium; its function is to greatly increase the surface area so that heat exchange is more efficient.

When the aluminium cooling “fan coil” is choked or dirty, the heat exchange properties will be reduced significantly. This means that the liquefied freon cannot be fully evaporated and thus the air conditioner is not very cold. Non-evaporated liquefied gas cannot be sent directly back into the compressor because liquid cannot be compressed, it will damage the 
compressor. That’s why they put in a liquid receiver.

When your heat exchanger is dirty and the gas do not fully evaporate, it will show a low gas pressure. If an untrained technician was to top up gas instead of properly cleaning up the system; he will cause the system to produce even more liquefied gas which already had difficulty evaporating.

When the amount of non-evaporated gas exceed the amount the liquid receiver can handle, it will damage the compressor. If you had top up the gas unnecessarily, your compressor will become very loud in the middle of the night; that’s because the room had cooled down and thus more non-evaporated liquefied gas is present. It is probably overflowing the liquid receiver. Get a qualified technician to investigate on the gas pressure immediately!