As a general rule, R134a is filled at around 80% of R12's weight.

An effective way to "guess" at the proper fill level is to observe the large return line to the compressor (near master cyl) for temp. Keep adding freon until you feel the line go cold, then stop. The onset of cooling happens quickly. If you overfill R134a, your heat transfer will fall off, so no benefit to bumping in too much.

Your pressure is dependent on temp and humidity, but in lieu of any numbers, I've found 50/250psig to be a default starting point. If you go negative on suction, you are low.....

Jim

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