Exactly, I have bypassed the heater valve control on the firewall which allows water to flow through the heater core at all times. If I leave it on the upper vents I get only cold air but if I have it on bi-level, floor or defrost it will open the flap and hot air will come out of those and the cold air still comes from the upper vents. Your control valve is either frozen open, the cable is frozen, broken, disconnected or bypassed like mine.