It's getting done the wrong way!
You can not find a leak under a vacuum! It will be pulling in moisture and dirt into the system if there is a leak!
Depending on how much gas is left in the system depends on the first step but let's say there is zero gas in the system,
step 1- connect gauges to confirm pressure
step 2- connect a bottle of OFN to gauges
step 3- turn bottle on and purge lines
step 4- test each side independently (if you can)
step 5- find leak (with whichever method that you like)
step 6- repair leak.
step 7- complete another possitive pressure test with OFN and make sure it holds!
step 8- vacuum system to an absolute
srep 9- weigh refrigerant into system according to data plate.
step 10- disconnect service equipment and close bonnet.
step 11- drive car with ice cold air blowing in your face!
Ive a feeling that every car you've ever had re-gassed was done via a machine?