What are you supposed to do with the old refrigerant? Aren’t you supposed to dispose it properly? How can you properly dispose the old refrigerant using the vacuum pump?
Some of the info in that article is not accurate. Also, some systems you DON’T want to just dump R134 into the low side as a liquid because if the low side port is too close to the compressor you can fuck it up. Before anyone blindly follows these instructions to charge your car please PM me or someone else who actually knows what they’re doing for advice.
Technically if there is anything left you should get a recovery machine and pull whats left and put it into a tank according to the EPA. Cars have such a minimal amount and if you dont have access to a recovery machine and tank good luck.
Very good point on not wanting to dump the 134A right in the low side all at once. I would try and get as much as I could on the high side first then slowly regulate it thru the low side taking a break every 10 to 15 seconds.