| Generally speaking, 57 PSI on R-12 is 60 Deg LIQUID.. if the system has sat for a while, and it's LESS then ~40 PSI High side and Low Side, then you have ONLY Gas in the system.. No Liquid.. so it's low on charge. So a System that is Less then ~5 PSI MIGHT have been opened, and the 'Re-Pressure' could have come from Freon Outgassing from the Oil after it was closed.. Generally I like to Pull the Charge out when it MIGHT be Vapor Only, then keep it in Vacuum to get all the containments out.. then charge it back with the proper amount of Refrigerant.. The Oil gets tricky.. it will be laying all around in the piping.. GENERALLY you want more than enough oil, as it will kill the compressor if it does not have enough.. BUT if you greatly overfill the system, it will be Oil Logged and run poorly.. or it will Hydro lock on the High Side and break something.. Generally an unknown system, needs to be Solvent Washed and blown with Air.. Brake Kleen Works as a solvent.. Remove the Compressor and Flush out the oil and put in Fresh Amount... then Change the Dryer and re-assemble right away and get it on a Vacuum for ~2-4 hours to get the solvent and air out.. then charge with the Proper Amount of Refrigerant..
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