I will add that if system has sat with 0 pressure in it, for more than a few weeks, you will also need to flush the system also. Here is why. When you have a leak pressure bleeds off. When pressure go's to 0, air will enter system. Nature adhores a vacuum. The air now in the system reacts with the oil in the system. Acids are formed that start destroying ac parts.
To get the acids and sludge out, system will have to be opened and flushed to get rid of the system destroying contaminants. A vacuum alone won't do the job.
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