There is no short cut to ac performance.If its blowing hot air,its probably a low charge.Why a low charge? Because you have a leak.AC systems are expensive to fix,and a good system wont act up for years,a worn out leaky system will cause constant problems.You put in 134a,you leak out 134a....basically its illegal.You cannot knowingly purge 134a into the atmosphere.Not that the feds will come get you,but just knowing that the leak you have is illegal,will make you want to fix it for real or else rip out the whole AC system (and save a bunch of weight and underhood clutter at the same time).