Hello,

I am in the process of replacing an old honeywell thermostat (Q539A1014) that was installed by a HVAC prof. about two years ago. We wanted to upgrade to a programmable thermostat.

We purchased a RTH6300B Honeywell. I was told by the home improvement store this was compatible and an easy switch.

The old model has the following:Terminal designations: R,W,Y,B,G,O. Single transormer conventional heating-cooling systems.

The connections on the old unit (the colors matched the letters and this was wired by a professional, so I assumed it was correct)

R- red wire
W- white wire
G- green wire
Y- yellow wire
O-none
B-blue

New t-stat:
G-green
W O/B- white
Not used
Y- yellow
R- red
RC-none

I am not sure what to do with the blue wire. We didn't use it and now the outside AC unit is not functioning. The inside fan is running. Not sure if I should connect the blue, if I programmed the unit incorrectly, or if I should call a professional.

I thought this would be easy, but I was mistaken!

Turn off power first then put a jumper between "R and RC", disconnect white wire and put blue to "W,O/B" terminal. The white wire may be for a aux. heater (electric heat strips) tape off for now, if you do have heat strips you need a two stage heat pump thermostat .Program thermostat for "B" in heating mode.
Good luck. Mike

I just tried this and nothing happened. It was very easy to install but if it doesn't work... well what?

Is this the same post as the other?