Use the following at your own risk lol:
The correct way is to fill the system with nitrogen or another inert gas with low to zero moisture but…
I have put the yellow vacuum line on the output side of the vacuum pump to pressurize the system without wasting refrigerant, then sprayed soapy water everywhere to find a leak. You’ll be filing it with atmospheric air that’s full of moisture so do with that information what you will.
The correct way is to fill the system with nitrogen or another inert gas with low to zero moisture but…
I have put the yellow vacuum line on the output side of the vacuum pump to pressurize the system without wasting refrigerant, then sprayed soapy water everywhere to find a leak. You’ll be filing it with atmospheric air that’s full of moisture so do with that information what you will.