The most common cause of leak in air conditioning systems is the condenser. It looks just like the radiator in your car, and in fact it's positioned directly in front of your radiator in the main air stream. Its purpose is to condense the high pressure gas produced by the compressor into a high pressure liquid. They can suffer damage from being hit by stones which are thrown up by other vehicles on the road.

Other components of the system use 'O' ring type seals. These can dry out if the system is not used and so will cause leaks. When air conditioning systems are re-gassed a dye which shows up under ultra-violet light is put in along with the R134a refridgerant. This dye is to enable leaks to be located easily.

It is important that the correct amount of refridgerant is put into the system, as too much or too little will result in poor performance.