I am also not an automotive AC expert...
It seems right to point out that the RENIX era XJs all came with Frigidaire (GM) compressors. My 1987 XJ was converted to R134a before I bought it. However, I will need to charge it soon and am really interested in the operation of these valves on the compressor. Can somebody (8Mud possibly) please explain in detail the operation of these valves, including direction of turn (CW or CCW)? Sorry for the hijack, I hope I added some value.