I am trying to install a new thermostat which requires a common wire for use. I however only have a Y,O,R, and G currently. There is a blue wire in the bundle that was installed however at the 24V transformer it is not connected... Is there an easy fix or do I need a transformer with a common wire hookup?? Thanks

You can use this blue wire for a common wire, just connect it to the transformer terminal that is opposite the terminal that the red wire to the thermostat is connected to, connect this blue wire to "C" at thermostat