I'd also replace the drier. If the system's been open to atmosphere, or contaminated by leakage, the drier dessiccant is probably no good (especially if it was the original installed 25 years ago.) If you find lots of swarf or other metal bits in it, then you probably have more severe problems such as a worn compressor. A Mini A/C unit needs all the efficiency it can get, and an old, moisture-laden or contaminated drier will reduce that effectiveness considerably.

Did you flush the system to remove the oil? Assuming there is now no oil in the system the service manual should say how much oil either in total or per component. As far as 134a put the fan on high, max AC, vents all open, windows down. Find the ac lines that go in and out of the evaporator, when they are about an equal cold temp, add about 6 oz more. Fill from low side only, a bucket of hot tap water will help get the 134a in there. While this method is low tech it works at all atmospheric conditions, with no manifold or gages.

Ok, so checked and sure enough there was virtually no Freon in the system.  So we went ahead opened up the main hoses and flushed out the condenser, evaporator and main hose, and replaced all the orings.  Installed the adapters for the valves and tightened  everything back up and pulled vacuum.  Holding so far so might be ok.  But now I’m getting ready to add the oil and 134.  Question is how much of each I should put in?

Thanks.  I’ve done some AC work on my old Porsche so I know the basics but it’s been a while.  I haven’t got around to checking pressures yet but I’m assuming the system is probably empty.  If that is correct, then I’d rather refill and test with 134 as it is cheap and readily available.  I was told that I just need to replace the valves and Orings, vacuum out and put 134 oil in and should then be good to go with 134.  Since I don’t have much to lose, I’ll try this.  Any other items I should replace?

Is the AC compressor clutch engaging when you turn on the Ac system? That clutch needs to engage to spin up the pump to start moving refrigerant thru system. You can get the clutch to engage sometimes by giving it power or jumper around pressure switch w a paper clip. (System needs to see pressure for it to engage AC clutch. It should give you a little cooling if there is some refrigerant in the system. You can add small amounts of R12 or R12 substitute if there is a bit in there already. Too much is not good either.)

start with pressure check:
push valve, feel if it has any pressure.
I usually start diagnosing  leaks by pumping air into system. Listen for leaks, if you are lucky, leak is easy to diagnose. AC repair is pretty easy, buy a manual.

Stay with the R12 if you can it blows colder imo. Autorefridgerants.com sell a freon that can be used in place of regular freon and a Mini only uses about one can depending on the system/year, i have used their household freon with good results and you do not need a license to buy it.
Most leaks on the a/c in Mini's is usually the condenser which can be repaired.
I know of a friend that put R 134 freon in his R 12 system without changing anything and it worked fine for over two years until he sold it, not saying to do this but just charge the system and see what it does as sometimes the leaks are so small it takes a long time to leak out.
Or take it to an a/c shop and have it pumped down to see if it holds a vacuum, if it does re charge it if not find the leak it could just be an O ring seal.

good evening and welcome to MM Jwkil..  ping. Malsal.. he has done lots of work on Jap speck minis with AC.. I know you can buy spare AC parts off www.vancouverminiclub.ca  from Craigs.. / Hunters..  hope this helps.. later bc

I recently purchased a 1992 mini 1.3spi with air conditioning from Japan.  The air conditioner doesn't work, just blows warm air.  I'll probably need to convert to R134 and put Freon in at the least, and who knows what else.  I noticed our host and other mini sites don't stock any AC parts.  Can anyone offer advice on what it takes to convert to 134, and where to go for parts?