Thanks in advance for your help...

I just purchased a large older home, and I want to replace the thermostats. They are Honeywell Chronotherm III's and the digital display's are impossible to read. I'm thinking of replacing them with Hunter AutoSaver 550's. The house has a hydro air system, with A/C. All of the wiring connecting the theromostats is straight forward and with the W4 R5 Y6 terminals wired with corresponding colored wires in all the locations, with one exception. In the Master Bedroom there are 6 wires connected to the thermostat. The O W4 G R5 B Y6 terminals are wired with corresponding colored wires... based upon what I've seen in the Hunter 550 user manual the terminals available are W RH RC G Y O/B. The 550 has less terminals than the Honeywell.

I guess my question is do the O and B wires both go to the O/B terminal, or should it be wired differently? Can I even use the Hunter for this location, or should I pick the best of the Honeywell's and keep it connected to the 6 wires?

Thanks again,

Lou I.

I would try to figure pout what the sixth wire is connected to if anything. You might even luck in and find some documentation on the thermostat on Honeywell's web site. Don't suppose the former owner left any documentation. Sometimes there is stuff on or inside the furnace. If you figure out what the wire is doing, you may be able to figure out another way of getting it done.