Vader is still determined to keep working on turning Luke to the dark side, but he's equally determined to be a father to his son as well.

He gets Luke spare parts for his ship if he breaks down, grabs him food, gives him gifts. When Han is frozen Vader is all stern about Luke coming with him, until Luke cries and so Vader relents and promises they can thaw Han out back on his ship. And then there are the hugs...