2003 impala ls

Great site ,have a quetion..After charghing ac...35 low side 220 high side ....vent cools down to 45-50....then when i shut car off hiss sound for 25 sec or so. Is this norm ? thank:screwy:

Just recharged a Nissan Altima, and had the same thing with the hissing type sound. Went away after about a week. I did a full vacuum purge before putting the refrigerant.