This 6 yr. old unit quit suddenly when I was using the AC. I have replaced the contactor, then the transformer, but nothing works... no fan/AC/ or Heat. The red light on the control board is not on. Do you think there is a good chance this is the problem. So far the parts have only totaled $45, but the control board is $145, so I hate to replace it if it could be something else. Any help out there. (I am going through the troubleshooting guide and that is why I replaced the above.)Thanks so much.