I told my female I'd change her freon... I figured I've done it in my truck... so it will be the same story in her 2000 civic, right? Ha. The freon tank says I need to drain the system, then add the new freon... my step dad says other wise. Plus, I was looking at it, and couldn't decide which valve drained it... no clear marking that I could see. It was either the big one or the small one... help?