R12 uses mineral oil, R134 uses synthetic both are NOT compatible. You need to remove the mineral oil from the system before converting to R134. Syntthetic oil molecules are smaller than mineral oil and will leak pass it if seals are at fault. Check for leaks first.

The charging line is the larger (low pressure) line. Don't connect to the smaller diameter line, it is the high pressure line and may burst the can of R134! Make sure the right type of oil is added to the refrigent as well, otherwise the compressor will not last long.

And yes, do change the drier, old one will contaminate new R134.

Also, if you have not done this already, modify your AC heat exchanger (next to radiator) so that there is a larger separation between both. It makes both your engine and AC run cooler. I used 3 inch screws with plastic inserts to secure the AC unit.

Maybe one day I'll post a drawing on how to do this.

 

To properly retrofit a system you need to flush all the components with a solvent. Vacuuming the system down will remove little to no oil.

 

I can get you guys some if you want. Licensed to buy, hahaha so I can get all I want. Send me a PM too if you guys want some.