any a/c techs here?

[Boog]

All stock 1991 Chevy 1500
350 engine
88,000 actual miles
the R4 compressor was replaced maybe 8 years ago and converted to R134a at that time by someone else

The ac has been working just fine until last week when refrigerant spewed out of the pressure relief valve on the back of the compressor several times while running. It continued to cool fine until it bled off enough to make the compressor cycle quickly. I replaced that relief valve and recharged the system. Again working fine yesterday then this morning with gauges hooked up, within 4 minutes of cold startup the high side pressure shot up to over 350 psi then compressor locked up and began burning the belt up. I shut it off and the compressor was not locked up. Fully charged system.
While I was replacing the relief valve I took that opportunity to pull the hoses off the compressor to have a look for signs of compressor death. They were clean.
When it was running I noticed the high pressure line from condensor to the evaporator was cool and sweating and the accumulator wasn't as cold as I thought it should be. I am of the opinion there is a blockage that has occurred. But where? Where in the line is the orifice tube? Am I on the right track here?