No heat 98 Dodge Ram 1500

I am getting no heating out of my defrost or heater? I have checked the fluid level in the radiator and checked the hoses for any leaks. I cant even get heat when I turn the a/c on? It looks like the heater core is working and the damper is closing when I turn the temperture dial to warm, could there be another door internally that is not opening/closing inside the damper control unit?