Charge Weights - R12 to R134a

[addo]

The only reference I've seen was a "secondhand" document saying that 60% of the R12 charge weight for initial charging with R134a, was a good starting point.

Any further comments from the informed?

Thanks, Adam.

[MJM]

I've seen 2 documents, one says 70% is a good starting point. (ICI) I think. The other says the charge will be 80% to 90% of the R12 value (Electrolux, now ACC compressors) I guess that it will be charge somewhere near and check temperatures and pressures against the spec.
What are you doing about compressor oil?

Important note. My data is for integral fridge type coolers not A/Con. This may affect oil choice, we have the electric motor to consider. We have to control refrigerant charge weight more closely than split type systems. (our smallest charge weight is 32 grammes which leaves little room for error.)

[addo]

I passively rinsed the whole system free of oil, now it will be PAG.

Your charge data is interesting; with automotive swash plate compressors they warn of "liquid slugging" - perhaps this is the reason for a low percentage start point? I would not be surprised if you are closer at the end with your 80-90% figure.

[MJM]

I try to set the systems up with as little superheat as possible because I like to make sure that the evaporator is as full as possible. (within the limits of capillary control). I'm lucky because any minor liquid returns to the compressor meet a nice big hot electric motor. The motor also benefits from some extra cooling. The compressors are are small reciprocating hermetic jobs and to be fair the manufacturers shroud the inlet system from liquid very well.