I just did this today in my Tucson. The refrigerant I bought is EZ Chill from Walmart, its $23 including the hose and gauge assembly and instructions are very easy.

By reading the instructions, it did mention about an "ambient temp" where they define as the air temp of the work environment surrounding the vehicle. At that temp there is a corresponding Low Side Gauge pressure. And by just looking at the gauge needle pointing to green/yellow /red my pressure don't need to be filled. But LOL! I missed to check the table and so I charged it until the recomended pressure was reach. And it consume maybe half of the 18oz container. And yes, it cools better and faster now.

Again, I followed the procedure in the charging kit..Should I need to follow the sight glass method, then thank you, I'll pay $130 Ha!ha! ha!

Most refrigerant refill like the one I bought have "Leak Sealer"..ohh really?

Update: Also done with the 4Runner, its easier than the Tucson because the Low side is very accessible and it sucked the the remaining refrigerant fast! until stable recommended pressure was reached and so as emptied the can. I think I need to check it back when the outside temp rises to 90F plus, if the pressure drop then I'll buy another refill can.