I have an old Carrier Split system (cerca 1983) I replaced the gas valve, then the board. The only thing I haven't changed is the transformer. When the unit is on heat the burners ignite, but the blower will not come on. I have to put the fan in the "on" position to get the blower to come on. When in the "auto" position the blower doesn't come on, but the burners do. Can anyone help me?