today i went out driving and my AC is not hot but not cold. So i went to Autozone and bout 3 cans of r-134 and the little hose. well i got home and i hooked the hose up to the onlt fitting it would go on so i assumed it was right. I then opened the valve to the can but it wouldnt come out. do i need to empty my system before trying to add new r134 or what how come it wont come out of the can. could someone post some info that will help me please i need AC thanks