[webbch]

If the compressor is seized, you'll want to pull the orifice tube and check it...after having the system evacuated. If there's a lot of debris, you'll need to flush the lines and especially the condenser. Otherwise, a new compressor won't last long. A/C systems thrive on cleanliness. I kept my '90 on R-12, having picked up a tank of it a few years back. If you decide to convert, you'll definitely need to flush all the lines anyway, as R-134a and mineral oil (used on R-12 systems) are not compatible.

If you plan on doing any work on the A/C, then do yourself a favor and get an A/C gauge set so you can check the low and high side pressures. I suspect the high side needs a 3/16" flare to 1/4" flare adapter fitting if it's like my '90 K2500.