Heat Selector Cable?

I have a 1996 Toyota Tercel and the switch that turns my climate unit from Cold to Hot is not working. The air coming out of my vents is always warm and even when on cold its warm. I am hoping there is a way to fix this without replacing the entire unit. I just relocated to South Florida and its gonna get awful with no airconditioning this summer. If the unit must be replaced, anyone have an idea what its gonna cost.

M