I have a Rheem HP/AC unit. I want to replace the old Rheem Thermostat with a Honeywell RTH6350D programmable unit.

The old thermostat was wired:

Green wire to G terminal
Red wire to R terminal
Blue wire to B terminal
No connection to O terminal
Yellow wire to Y terminal
White wire to W2 terminal
Brown wire to X terminal
No connection to L terminal
Black wire to E terminal

On the new Thermostat I have connected:

Red to R
Yellow to Y
Blue to O/B
Green to G
White to Aux
Brown to E
Black HAS NO WHERE TO GO!

Can you assist