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.

