I can vouch for Freeze 12 as I used it in both my air conditioned Datsuns for years with no problems. It's much less costly than R12, requires less refrigerant and runs at a lower high side pressure than R12. I'm a licensed HVAC/MVAC tech and have tested a few R12 replacements/alternatives such as R414B (Hotshot), Red Tek 12, Freeze 12, Autofrost as well as R134a. You'll hear pros and cons for Freeze 12 as you would with any R12 alternative. IMO, for Freeze 12, the pros outweigh the cons.

I just had the car in for a checkup at the shop that rebuilt the A/C. They determined that there's an electrical problem -- the low pressure switch isn't coming on because it's not getting the juice it needs.

So somewhere in that car is a wire, connector, and/or harness that's shot. I imagine it's somewhere under the dash. Pity I can't just buy a new dash harness and install it.