why one side of dual zone climate control is blowing out heat

What is your question?

In the winter, the driver's side heat doesn't work. It blows out cold air, while the passenger side blows out heat. I have dual zone climate control. Both sides work fine in the summer....

What makes this problem better or worse?

Works fine in summer, not in winter

How long has your 2006 Lincoln Navigator had this problem?

about a year or so