The proper procedure would be to partially charge it and find and fix the leak. After repairing the leak, you should vacuum the system down to a negative pressure to ensure an air tight system and remove all traces of moisture. This will give you positive proof there is no other leak and ensure a good performing system. after a good vacuum test, add the specified amount of refrigerant (listed on a label near the low pressure port) and depending on the situation, you may have to add some lubricating oil. This is difficult to say how much because unless you remove and drain all the oil out, you cannot tell how much was lost. Some will be carried out with the leak and a lot if it was a sudden loss, I would add a few ounces to be safe. Add the oil first then start to fill the system with (refrigerant) with the engine off until it seems to slow and not take any more, then start the engine and turn on the A/C it should take the remaining refrigerant. check air outlet temps and ensure all connections, components and lines are leak free.
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