Hi,
I have a 92 sc400 also and the same thing happens. My friend tested it and found a leak of refrigerant, R12, at the evaporator pressure regulator connection in the line. My friend mostly works on American cars and said he didn't have the right tools to fix it. I found the part at a local (non chain) auto parts store for $33.00. The compressor stops working when you run out of R12 due to lack of pressure in the system, so your compressor may be OK. I haven't found a local mechanic that I trust to fix it yet, but I am looking. The local Lexus dealer has done shoddy, over priced work on my car 2x so I don't go to them anymore.
Any info from anyone out there would be greatly appreciated.
