I have central air and heat, with a Nest thermostat. My system has Y, G, R, C and W wires coming out of it:
which are wired into my Nest like so:
In between, there is a splice where the C wire is spliced with electric and another wire runs from that splice back to the C hookup:
And then the other wires are spliced with a new set of the same color:
The heat and cooling work fine. I just can't get the fan to run on its own. What could be at fault and how can I diagnose it?