I have an american standard ASYSTAT655A thermostat I want to replace with a 3M-30. I currently have the following wires on the american standard hooked up- Red-R, Blue-B, Yellow-Y, Green-G, Brown-X2, Orange-O, and White-W and linked to U. there is also a black wire that is not used. From the info I am reading this is a heat pump unit if that helps at all. I just want to know the wires I need to hook up for the new one. My confusion is with the X2 brown wire and the black wire. Along with the white being jumped to U.

Check you're connection at the Units end to locate all the wires going to each connection, then figure where or what they are for...