I have a 4 wire from my old thermostat... red, white green and blue. I have the red going to the RC... white to white... green to green but not sure where the blue wire should go? I can't get my thermostat to work.

Do you have ac? If so the blue goes to y post

Thank you but that doesn't seem to help. My heat was working fine and when I turned on my ac this year it keeps tripping the breaker.