Clicking noise and no heat

Over the summer I would hear a noise under the dash. A clicking noise that would only happen on occasion. I just couldnt figure it out. My A/C worked so I just disregarded it. Now it is freezing cold and my heater will not turn on. Each time I turn the dial from cold over to warm it starts loudly clicking and no heat comes out. At one point I opened and shut the vents virerously and it stopped but the heat never got very hot, just slightly warm. Now its back to no heat and loudly clicking! I am not quite sure what it is and have had an estimate for the heating element but I am nervous that is not all the is weong