Superheat of TXV should be adjusted at commissioning or replacement of valve.
Superheat should be adjusted at about 65% of evaporator design TD when ambient temperature of cooling equipment is 1-2 K near design temperature.
Subcooling should be adjusted with refrigerant charge when ambient temperature is near design temperature. Condenser could be partially covered to get that design condensation temperature. Than when unit is at near inside design temperature and outside design temperature, charge should be adjusted to about 7K subcooling for R404A. Do not rely on sight-glass, since it sometimes could still have bubbles at that subcooling.
At -40°C ambient, evaporator (dynamic) TD is about 4-5K and superheat should be around 3K.
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