Have a 15 Seer Lennox heat pump system that the liquid line is sweating in heat pump mode for about 8' out of the air handler. It only does it in heat pump. R/410a system. Wonder if the reversing valve is switching when the call for heat ends, but I couldn't catch it doing it.
Copper line is turning green too. It doesn't seem to be sweating while it's running, but was wet when I got there and the system had cycled off.