As for mixing the old freon with the new.....one of my dads buddies owns a car lot and they have been doing it for years, never had a problem. Most of the kits out there come with oils and such that seem to help in the tow different freons living together. GL...I know I gotta figure out what the problem is in my GSR, sounds just like yours.....system is full yet it only blows "kinda" cool air...SUCK on really hot days! lol