Heater issues on 02 TB

My driver side blows cold all the time. I can control the passenger side, but not the driver side. Its really cold outside these days and am really missing my heater!!! Is this a control problem or a problem within the dash or wiring??

My 02 trailblazer acts up when I set the heat control halfway between hot and cold and it will only blow hot air. I have to shut it off set it to cold so it will blow cold air again. So I either leave it on hot then switch to cold and vise versa if it is a semi warm day, otherwise I will roast to death. Also, the passengers side climate control seems to control both sides for hot and cold???