I am installing a new thermostat and need help with the wiring since the old wires don't exactly match what seem to be the standard setup. I have four wires coming out of the wall: red, green, yellow, and blue. The are connected to terminals in the old thermostat labeled, respectively: R, G, Y, B/D. I'm guessing the red=power, the green=fan, the yellow=cool, and blue=heat, and no common wire. Does this sound right? If I'm wrong, am I running a huge risk hooking it up this way and testing it out? Thanks!