One of our favorite “Go-to-a-licensed-professional-for-AC-system-charging” stories involves a guy we spent more time than we care to admit troubleshooting before it became apparent that he was releasing the vacuum before charging. His thinking: “I checked for leaks, now I’m moving on to the next step.” He was not only evacuating and charging without a license but without any understanding of what he was doing. Please, if you are not a licensed AC professional, do not evacuate/charge on your own. Go to a licensed professional. It’s worth it to get it done right. That said, we’ve run into many experienced car guys who don’t really understand evacuation and decided a quick summary would be helpful to even licensed AC professionals.