[einstein]

Gents, its been decades since I've dealt with these symptoms, could use some tribal knowledge.

Looks like a never-opened factory system, even though 28 years old and 230k miles.

Earlier this year after topping up the R134, the vents blew ~36° F. High side Schrader leaks a bit, and another top-up results in 45° at idle and stationary, but within a mile driving highway it warms up to about ambient, 80-90°F. Won't clear the windshield in rain either, so I'm considering my safety as well as comfort.

Did I poison the system with a bit of moisture or atmospheric air?

Or am I looking at other possibilities, like crud in the orifice tube, blockage somewhere, weakened compressor or whatever?

[Lemans64]

Without putting some gauges on it, pretty hard to tell. But they did have lots of problems with the cycling switch that screws onto accumulator by firewall.
try tapping on the switch to see if compressor engages. Sounds as though the compressor is not coming on?

[einstein]

Good callout. Thank you. I'll look for a new switch.

Worked on it last evening. Pressures at idle with ambient about 85° are 170/28. I held throttle up over 2,000 and the compressor cycled off and wouldn't come back on.

Before that, I'd pulled the fan to inspect the evaporator after seeing a video of one with the fins plugged. Was rather cruddy after 28 years.

Sprayed diluted Dawn on it, let it soak, then used shop-vac with a smaller hose rigged up to suck all that crud out.