1987 300D A/C just quit - anybody have a schematic?

Was driving the other day and it just suddenly quit and started blowing ambient air.

Got home and tried listening for the compressor engaging when I dialed-up 'max cool'. No clutch click. Checked pressure - don't see anything in the sightglass because there's no flow but I have >140PSI in a hot system - it SHOULD be enough pressure for the cutout sensor. Fuse (#7) is okay because the blower runs.

I don't have my metering handy so I can't start electrical checks for a couple of days. There was oil the last time I burped the high-side connector - looked reasonably clean. No visible leaks - I shouldn't have lost any oil. Had UV tracer in it from last year and I see nothing under UV light. Can't add oil or tracer now since I can't get a pressure drop. It's an R12 system, with a rebuilt R134 compressor, running 'Freeze-12' refrigerant (which is good for both '12 & '134 systems & seals & pressures & oils).

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My Haynes book sucks when it comes to A/C - you can tear down brakes & steering & suspension and do other things that can kill you if you've screwed up, but they say A/C is dangerous black magic and should only be done by pros. Not even a schematic. F-'em.

Any help greatly appreciated. Thanks.