Colman heat pump sub cooling or super heat

No matter what brand, size or refrigerant I watch the whole picture as I charge. Older units with beat up or corroded coils can't take a lot of sub cooling without pushing the head psi too high. FWIW, Cap tubes are a crude device, those tiny filter driers are usually poor quality and the mfgrs often don't do a good evacuation so there's a good chance of improving the cooling on even a new AC by redoing them right. Sub cooling is paramount for increasing net refrigeration effect (NRE) as long as everything else looks good. I've installed a split system w/txv that would handle 17 degrees SC and T sat was only 20 degrees over ambient. With a cap tube, you're also limited by superheat. Say the SH is down to 10 degrees and the SC is only 1 degrees or so.... You're stuck with that. Or if the SC is only 1 degree or so and the T sat is sky high, like 30 over ambient and SH is still too high... You've got a big problem. Sorry if you already know all this stuff but this is what makes it so interesting and fun! So anyway, I'm happy if I can get only 5 degrees SC or even less, if T sat is around 20 over ambient and SH is down to 10 or so. That's for high SEER units and a clean coil. You have to adjust for the equipment condition and efficiency. Get the SH down to 10-12 and watch the head psi and hopefully you'll have a few degrees or more SC and T sat that's good... 20 or a little more, over ambient. But... If the SH is down to 10-12 and you don't have much, or no SC and T sat is good, that's also fine for a cap tube. You can't count on SC with a cap tube and that's why a liquid line sight glass ahead of a cap tube is worthless. Good luck! Craig