Just a note of caution to everybody, use guys that have the right equipment, it costs a little more, but in the long run can save you alot of money. (The guys next to the road cost me R6000.00).
Problem is if they put to much gas in, it is nice and cool, but puts the compressor under a high load and can cause it to pack up. The correct way to do it, is for them to first suck out all the old gas, the old gas can become stale and if you just add gas you could need a regas after 2 or 3 months again and it will make cold but not as cold as before, and then just adding gas can overload your pipes and most importantly the compressor. Secondly the machine that removes the old gas creates a vacuum in the system for two reasons. 1. After removing the gas it tests to see if there are any leaks before filling again, if leaks are found, it must be fixed first and here is the second reason, if any air leaks into the system, it can cause condensation in the pipes and with the gas that is used forms a acid like substance that over time eats through the aircon pipes. When the machine injects the new gas it also adds special fluorescent oil that helps to keep the system and o-rings oiled, and should a leak occur, it can easily be picked up with a ultraviolet light.