I've started restoring the A/C system on my RX, and it has not been an easy journey as far as parts go. Mostly this is because the system is Panasonic, which has a couple odd parts, namely the receiver drier: it has the pressure switch screwed into the drier body as opposed to most other cars (and the Hitachi system) where the pressure switch has a place on the refrigerant line between the condenser and the drier. I tried one (made by Metra or something like that) that looked correct and was specified for the '88 Panasonic system, but it is very wrong: the IN and OUT ports are reversed, its fittings are the wrong thread size, and it doesn't have a place for the pressure switch to be mounted, not to mention that it's taller and slimmer than the original so it wouldn't fit quite right regardless.
Now, I can use the interwebs to find about 10 different drier models that say they fit this system, and they may look compatible judging by the right-angle flanges, but none provide any real information (namely about the port size, flow direction, and the pressure switch fitting) and I'd rather not have to buy all 10 of them just to find one (or none) that work. Does anybody know of a tried-and-true replacement? I'll call the dealer to see if they offer one with the new R134a-type dessicant for a reasonable price.
The other part that can be problematic is the thermal expansion valve: the Hitachi system has a third, smaller refrigerant tube with a fitting in addition to the two main fittings and the thermal bulb whereas the Panasonic system lacks this third tube. Most places will say that the Hitachi valve fits the Panasonic system; it does not. I decided I didn't want to play with it, so I just replaced the o-rings and put the original valve back on since there were no overt signs of failure or contamination or anything. If I do end up replacing it, my '88 RX-7 uses the same style valve (I know because last year I restored my 7's A/C system), so I'll order one for that car instead.
Otherwise, a generic HBNR o-ring set and R134a adapter kit are all I needed. I decided to use POE oil instead of PAG because the original compressor is still good and PAG supposedly doesn't like residual mineral oil and any chlorine that may have been left behind by the old R12 charge. I've already drained the old oil from the compressor and reinstalled it, flushed the evaporator and condenser, and replaced all of the o-rings. Once I have the proper receiver drier, I can oil up the compressor, evac the system, and charge it. I also modified the HVAC control so that I can run the A/C system (or not run it) in any climate control position.