You cannot check subcooling at split-system refrigerant charging/evacuation port in cooling mode! You can only check superheat!
In heating mode, at that point, you can only check total superheat.
Corect charge is checked by weighing refrigerant.
Corect operation is checked by measuring air properties!
For other measurments, you need to install test points and/or use thermal camera and termocouples at apropriate system points to obtain temperature diferences.