It helps to know what you're looking at. The SC that you select at the top of the chart is the "required subcooling" and that would be what is listed on the nameplate, and that differs fom one model to another, and even from one size to another of the same model. The chart is for use across the entire product line, it's generic, thus the reason for the range from 8 to 18. In this case the required subcooling is 15°. You use the column below 15° and ignore the other columns. HTH. That chart is only for those who don't know how to subtract LLT from SCT. Ironically there is no 15° column, so you're expected to interpolate. I don't know how a tech who can't subtract is going to manage that, but there you go. That's how you use the chart.
There are also a range of favorable conditions under which that SC value is valid. Instructions are to weigh in the charge when conditions aren't favorable and come back later when they ARE favorable to trim the charge.
Thanks. Based on the chart, the subcooling seems correct, assuming the unit was in second stage when the pressure and temps were taken. I have no idea of what the pressure difference is between 1st & 2nd stage. I have no experience with 2 stage compressors.
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