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Thread: AC Pressures

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    AC Pressures

    Does anyone know if a conversion factor is needed to determine how much r-134 is needed when servicing a converted R-12 system? My 93 was converted over by the previous owner but aside from new fittings, there is no documentation. Also, the high and low side pressures are different between gasses. and am not sure which to use. I was going to use PAG oil to top off the system since ester oil should already be there to blend the two oils from the conversion. Worst case, I was gonna put approx 1.5 lb into the system and see what happens. I figure the compressor will make noise pretty quick if it is low on oil. And as long as I don't exceed the working pressures for R-12, I shouldn't rupture the system.

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    6S Moderator S.Bretz's Avatar
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    1.5lbs of oil? Or 134? If 1.5lbs of oil, that is TOO much. You can add 2oz if you want to top it off on oil but adding too much will take up too much space in the system and it can reduce the performance.
    There is a conversion when going from r12 to r134. I don't know it but a google search should pull it up.
    If you have a machine that reads high and low sides I would start with 1.5-2 lbs of r134 and watch the line pressures. You want 35-40 psi on the low side and 180-200 ish on the high side. The high side may be a little higher is the temp is hot but you shouldn't really be going over 220-230ish.
    -6S Resident Mechanical Forensics member #001.
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    Haha, sorry. I meant 1.5 lb of refrigerant. Best I can find for a conversion is to aim for 80% of recommended r-12 fill. I tried filling it the other night. Got a can in and the high pressure line started weeping. Odd that it held vacuum but leaked as the system built pressure. Waiting on a new hose to try again.

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