I'm replacing a Rheem thermostat with a Honeywell 6300 for an electric heating/ac unit and I'm having trouble matching up the wire colors. The Rheem thermostat is one of the old ones with the mercury, so the wires aren't labeled only color coded. The Rheem thermostat has a yellow, blue, red, white, and black wire. I'm not sure what letters the black and blue wires should go to.


Proposed connections using Honewell RTH 6300B Tstat

Wire ----> Connected to -> T-stat
--------------------------------

Red -----> Connected to -> R
White ---> Connected to -> W
Yellow --> Connected to -> Y
Black ---> Connected to -> ???
Blue ----> Connected to -> ???

Thanks

Either the blue or the black wire has to be used to energize the fan, and one wire will probably be your common. You should check at the heating unit to see which wire goes where.