Heater blows hot one side and cold the other

What is your question?

I have a 2001 Doddge stratus 3.0, the heater core has been replaced, worked fine for months, now when I turn on the heat, defrosters, or vent positions, hot air comes from the passenger side and cold from the driver. Have taken dash out, looking right into the heater box, air comming out on right side is hot left side is cold. Any help greatly appreciated.