So I've never had AC in my wrx and two weeks ago I charged it fully. It was working great for a couple of days...since then it was pretty cold so I haven't used it..the other day i tried to turn my ac on and all i heard was a hissing noise and the ac was not cold at all..i had charged it all the way two weeks ago but apparently it had all leaked out..the hissing noise was nonstop as long as the ac was turned on...i tried recharging the ac again but this time I only charged it for about 5 minutes cause I had to run an errand and the AC was blowing cold even tho i may hav not charged it all the way..now everytime i turn on the AC it hisses for about 10-20 seconds depending on how long i havent used the ac..if i didnt use the ac for a day it would hiss for 20 seconds then go away and the ac would blow cold..whereas if i used the ac earlier in the day and then later at night it would hiss for 10 seconds then go away..I'm not quite sure what I am suppose to do at this point..somebody help!

i hear hissing too at the begining

update: ac no longer cold..so somethings leaking i guess?

Take it to a shop that does AC work and have it fixed properly. This isn't a DIY repair unless you have the right equipment and knowledge. A can of refrigerant from the parts store isn't going to get it working especially if the system was nonfunctional/empty for a long time.