re: Larger copper line on my outside AC was frozen yesterday...advice?

Restriction in system or low Freon. If it is frozen outside chances are the evaporator coil in upper unit is also froze up. Quick solution cut a/c off on thermostat and run fan only for 45-60 minutes. As the fan pull warm hot air from inside the house through the air return it will cause the ice to thaw on evaporator coil down to low pressure line outside.