A/C temp

Your system wasn't designed for 134a. To fully charge the system would bust hoses, etc... The only way to use 134a is to use less of it.
If you know what a fixed orifice tube is, yor system doesn't have that either.
Your system does however have a screen at the line in or high pressure side of your expansion valve similar to the one on a fixed orifice tube. This is a stack of cone shaped screens and should be removed , cleaned, and reinstalled. All you can do is move as much of the gas as possible in the older systems. It will never perform like a true 134a system or get as cold as r12 did.