2000 Ford Windstar Front heater blows cold air

When I turn the heater/defroster on in the front of the cabin it only blows cold air. Also if I toggle the controls from either hot->cold or vise versa it will click repeatedly about every 2-3 seconds until I switch it back. The heat in the rear of the cabin works fine whether I use the rear control panel or the same control panel my front heater uses. Any ideas what this could be? I am trying to see if this is something I can fix myself or get an estimate to have it fixed so I know how much I will need to save. Thanks