At the beginning of this act, John Proctor says, “It is winter in here yet, Why is this pertinent to what is going on?

Proctor is making a statement about the emotional condition of his home. Feelings between Proctor and Elizabeth have deteriorated to the point where they have "nothing." Their home is not a home, it's lacks the "warmth" of a family. The house is filled with furniture and people live there, but no one is really living; it's just "cold" and empty.