Hi I have a York Furnace with a White-Rodgers 50a51-242 control board and need a common for a Honeywell WiFi thermostat. There is no Common "C" terminal identified on the control board, but there is a "B" terminal. I have seen other versions of this board with this same terminal labeled "B/C". Here's the problem. When I try to use the "B" terminal for the common, everything comes on (fan, flame, A/C) when the thermostat calls for A/C. Board and furnace works fine with a honeywell 4-wire thermostat. Any other option for a common terminal?
One item to add, when testing the 5-wire thermostat, I was testing at the furnace with a brand new piece of 5 wire thermostat wire about 4 feet long. Just to make sure I didn't have a short in the legacy wire somewhere.