Anyone know a good way to check the A/C in the winter short of trying to run it in a heated (but ventilated) garage? It's a 1982 300SD with an R12 system, and the only test I know of (run in defrost, verify compressor clutch engages to demonstrate that there is SOME freon pressure in the system) was good.

It's an otherwise near-immaculate low-milage (140K) 82 300SD that, aside from some suspension rubber (expected) and a little idle shake (31 year old motor mounts and 20k since the last valve adjustment) is an obvious buy.

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1992 300D 2.5T 249k - Parked with a bad transmission
1981 300SD 142k - Daily driver