Properly fitted ACs will not leak refrigerant and there is no need to add refrigerant every year. If refrigerant gets low, it means there is a leak and Xulfiqar has pointed out the right way to check for leaks He is also right in saying that all AC installations require the lines to be vacuumed, however no one follows this procedure. If you have any doubt about this then you should read the installation manual that came with your air conditioner.
As far as I know there is no such thing as local gas. There are two varieties, one is sourced from China, the other is American. One cylinder contains about 10kg refrigerant which is enough to fill 10 completely empty 1 ton units. The Chinese cylinder is selling for 3700, the American cylinder manufactured by Honeywell is for Rs. 6000. This is the price as quoted by a dealer of AC components. You can't go wrong with Honeywell, however there are some Chinese which are just as good as American Honeywell. This is what the dealer claims. However installers will charge you a minimum of Rs. 1000 for topping up the gas. Almost every installer in the market uses Chinese refrigerant, for the simple reason that it saves them more money.
But if an installer shows you an original Honeywell cylinder you still can't be sure that the gas inside also comes from Honeywell, because they can get any old cylinder refilled with any kind of gas.
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