The A/C tech will do that. It is critical to evacuate and test the system, then put in a weighed amount of refrigerant. Those DIY kits on store shelves (except California, where they are illegal) have destroyed countless compressors because the instructions are bogus. It is impossible to tell the amount of charge with pressure gauges and a few ounces too little starves the compressor of oil; a few ounces too much spills slugs of liquid refrigerant into the compressor where it has the same effect that chewing on rocks has on teeth. I no longer answer questions from people who have killed their A/C trying to charge it at home; it is too sad.

if you have to ask on an AC system you lack the knowledge and tools required to do it. If you try it and you release Freon into the air it is illegal and there is a chance of going blind if you get it into your eyes (Pressurized Freon and oil).There are more ways you could hurt yourself working on an AC system as well. The store Freon (most small cans has 2oz of oil in each can). you will plug the system with oil and you will have reduced cooling the cars inside affect. so all in all " Don't mess with the AC system let professionals do it so you don't hurt yourself". You have to do a leak test, find and fix leak. you have to recover the Freon to fix the leak. you have to know how to recharge properly. how much oil what kind of oil and how much Freon and what kind.I use dye to locate the leak (you need to know how much dye to use in that system" fixing AC's is easy once you learn how and that takes a while to learn all that you need to know. The license only tells you how to handle the Freon not usage on vehicles but it does give you guide lines. So after that then you need to have someone show you and that takes years to learn.

If you have to ask, you have a 90% chance of frying the system they your out big bucks Things under pressure you know. Put it in the wrong side Open your wallet all the way, then turn your head cause a tech is going to rape your wallet fixing it.

Hope it helps

the chances of any garage evacuating the system , testing it and recharging as per the manual are minimal try a top up kit but don't put any more oil in

You take it to a garage and they will do it. If you need it though then you have a leak that needs sorting first.