Yeah, it does not make any sense to disconnect the hoses and reconnect it later. When you will try to reconnect, air will get in, and you do not want to put expensive R12 with air already in it. You have to use proper tools, like a pressure gauge and proper hoses to be able to vaccum and charge the unit properly, it does not seem like this is the right mechanic if he does not have these tools. R12 is very expensive so dont charge the system using this reconnect-disconnect method, go to an auto air shop.

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Saumil S. Patel