Air conditioning works by compressing a refridgerant gas (R134a) which increases it's pressure and therefore temperature. This high pressure gas passes through a condenser where the gas condenses into a high pressure liquid. The liquid then goes to an expansion valve where it's pressure is substantially reduced and consequently so is it's temperature, and then on into the evaporator where outside heat is absorbed and the liquid evaporates back into a gas. The low pressure gas is then drawn back through a receiver dryer to the compressor where the whole process starts again.

It's a closed loop system and the amount of gas has to be correct for the system to function properly. Too much gas will mean the system will be just as ineffective as too little. In addition to the legalities, and since you have no way of knowing how much gas is in the system to start with you should take the previous poster's advice and take it to a professional with the right equipment.....

Edited by Railroad. on 29/07/2010 at 21:48