, there's differing information on AlfaBB about what's required to change to R134a, and how detrimental the mineral oil lubricant used with R12 is to R134a. There are supposedly products on the market that will flush the system of old lubricant. Some folks advocate changing the compressor and dryer regardless.
My AC hasn't worked since I've owned the car, almost 5 years now. In addition, I've removed the under-dash assembly a couple of times, to work on the heater core. So, I cannot trust anything the PO may have done, and the system has been open to the air on at least two occasions.
I'll tell you what I did in my case, so you can decide for yourself:
- Replaced the compressor. Mine was obviously bad, and needed replacing anyway, $130. I did it while I had the engine out of the car. (It sounds like @Susan
retained her original compressor.
- Replaced the dryer/accumulator. I've read to do this anytime the system has been opened up to the air. Not a big deal: Part# 80-8080, $19.99 at O'Reilley's. It won't come up as an Alfa replacement item if you search, but it fits and connects perfectly.
- Replaced all the o-rings in the system. I bought a blister pack of assorted green AC o-rings, $6. (possibly optional for you)
- R12 to R134a adapters. I discovered that I needed an adapter to mate the 'snap-on' R134a connector of the recharge kit to the threaded R12 connector on the compressor. A blister pack with the low pressure adapter and two different high-pressure adapters was $10. I tried to do a search on O'Reilly's site, but couldn't find it; ask the counter help for assistance. I wish I had put the adapter on before I installed the engine; it's a tough reach with all the intake stuff installed. Also, be careful when installing the adapter (16mm in my case) that your socket is not also engaging the nut of the compressor's fitting. I caught myself in time before I stripped out the port.
- Recharge kit, $34.
I replaced the o-rings and the dryer. I removed the coolant overflow tank, and installed the low-pressure adapter on the S (suction) port of the compressor. With the engine running and the AC on high, I slightly loosened the suction hose, and let the system purge itself. A little mineral oil blew out onto the compressor housing, I tightened the hose, shut off the AC and engine, then wiped up the mineral oil. I then connected the recharge kit, and followed the instructions. The instructions are a bit oddly-worded, so read everything before you do anything. When finished, I disconnected the kit and reinstalled the overflow tank.
I am quite pleased with the results, and the system seems to be holding pressure well.