Heater routing problem

My heat selector switch is not working. Air is blowing from the top front vents but when i move the switch to the floor or the front windsheild, nothing happens. While driving it sometimes switches to the windsheild by itself. Also sometimes I get hot air but most of the time it blows cold. I dont want to spend a lot of money on this vehicle so if anyone can give me suggestions on what may be the problem and how I my be able to fix this myself it would be greatly appreciated.

What year?

Sorry, 1998 Grand Caravan