Is the system still under pressure? Yes or No.
Cause, IF the system was NOT under pressure.........then, why the need to evacuate it?
IF it is under pressure then, yes, evacuation is needed to capture the refrigerant.
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Next, parts replacement. Add new "correct" oil to the replacement part (check what the book says about the amount and type). Change the orifice tube (why not, since you're already evacuated). Button up the system using new "correct" O rings and lube. Then, hook up your gauge set. Evacuate (AKA: Vacuum) the system for say, half an hour (an hour is better). Then, stop and check for leaks (say 15-30 mins.). IF it holds the vacuum, you're GTG..........continue w/ re-charge steps. Check the book for the correct type and amount.
Anyway: The point of evacuation (vacuum) prior to a re-charge (beside, leak testing), is to "boil out" any air that may have gotten into the system lines and parts, when the system was opened. You don't want any air in the system. Only the correct refrigerant gas.
Aloha, Mark