I have a thermostat that needs 24VAC. I have the step down transformer but am not sure how to integrate it into the system. There are 4 wires between the Handler and the Thermostat (R, W, G, Y). The blue is there but not connected to anything. Do I hook up the transformer to an standard outlet, if so what two wire do I connect to the output side (I assume one would be blue, and possibly red)? Do I disconnect the red from it current source to hook to the output side of transformer? Are the black and white needed to be looped into the HVAC power or can it be totally separate?

Does the tstat have a c post?

Yes it does. Thanks in advance!