Charging a goodman in winter.

[m_l_ca]

So I have installed a Goodman 3-ton, R410a, TXV system. 3/8 liquid line and 7/8 suction. The unit came charged for 15' of tube. I have approximately 25 - 30' and an A-coil. How would I determine the extra refrigerant to be added.
Also, in regards to charging via subcooling, I live in Canada and the outside temp can get down to -15C this time of year. Any suggestions or info would help :)

[Magoo]

The installation manual will stipulate the system charge for maximum pipe run. And will also state added charge for extended pipe runs, probably grams not kilograms

[nike123]

Calculate volume of liquid refrigerant in your extra length of connection line with smaller diameter and convert that in weight by using specific volume of liquid refrigerant at lowest operating pressure in heating and that is your amount of refrigerant which should be added.

Or, read installation manual.;)