ac rear blower problem

For some reason my rear blower will run most of the time, even after all knobs are off. Sometimes it will turn off by its self, then back on. I checked the relays adn they are fine. Also my vents in the front work kinda weird too. They never stop blowing air. You have to play with it to get the defroster to blow by its self. I have 67000 miles. What could I look into to fix it?