I vacuumed and re-filled by AC with R134a. It worked great initially, got weak over time and is blowing warm air now. Low side pressure is too low. I see some green residue on the inside part of the cap? I suspect that somebody tried to diagnose the AC before me, and it may be the green dye. I got a cheap "kit" with caps and schrader valves, but have not installed it yet. It does not look like the replacement caps are threaded (Jaguar ones are). There seem to be more than a few different variations of AC charge port caps, with different threads (M9x1, M8x1, etc.) online. What are the correct charge port caps for 2000 XK8 and where can I buy a set? I am thinking about replacing schrader valves for good practice (they are suspect). I got conflicting opinions as to the importance of the cap for sealing the lines. I expected the schrader valve to be the main part providing the seal, and the cap to keep the dirt out, but some online sources claim that properly sealed caps are really important. I am new to AC repair (mostly I am an engine guy). If somebody could shed some light on the AC charge port caps question, I would really appreciate it.