Charging in the winter is best done by weighing in the charge, when starting with an empty system. Most manufacturers publish pressure charts for the winter, but they are not very accurate, due to differences in indoor air flow and indoor and outdoor conditions. It is best to check charge in cooling season with outdoor temps at least
75 degrees. Charging is then done done by subcooling for expansion valve systems and by suction superheat for piston metering devices.
When charging in the winter, pressures in the system are lower, but pressures in the refrigerant drum are also lower.
When you charge by weight, you must know the charge for the outdoor unit and indoor coil, as well as the refrigerant line length and tubing diameter as they affect correct charge as well as the units.
It is just best to check it in the cooling season when there is load on the system. It is best to let it run 15 minutes to let the temperatures and pressures stabilize.
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