I have a 2006 Ford Five Hundred. And the heat is not working in the vehicle. I have trouble shooted the vehicle and I know that it's not the heater core. Or I think. I had a problem with the A.C. in the summer where it was only blowing hot air and I reset the blend door acuator and finally I had cold air. But since then I have not had any heat. I was wondering if anyone can give me some advice on this issue? I was wondering if it might be a realy or something. Please Help!!!