What happens when you add more than enough Freon?

I have a 2003 Mitsubishi Eclipse & I was thinking about adding freon to the A/C but I don't have the meter than tells you how much freon is in there already. I just have a hose to connect the freon to it. Since I'm not going to be able to read how much freon is in there, what happens if I add more freon than it should have? Or will it stop automatically when it's full?? Thanks In advance :)