If I understand what you are saying - you don't trust the gauge?

I considered that the gauge might be shot, but I haven't used it since I took those readings, so I can't see why it would all of a sudden fail without warning.

I went to Kragen to see if they had a way that I could test my gauge, or one that I could borrow and use on my car, but they didn't. The guy suggested that a bad accumulator or evaporator would keep the system from maintaining pressure.

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'81 300SD

Connect your gauge to a known-good vehicle and see what it say's.

I thought about that, but Summer might be over by the time I find a vehicle around here with a working R12 system

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'81 300SD

Use compressed air with a rubber tip to check if the gauges work. Don't forget to open the valves or you won't get a reading. It's more likely you did not connect the gauges properly.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked