I have a two-zone gas hot air and air conditioning furnace. Main level thermostat controls mail level, upstairs tstat controls upstairs.

Main control panel on the furnace takes in wires from both thermostats:
Zone 1:
G, B, O, Y, W, and R

Zone 2:
R, Y, W

Zone 1 controls heating/cooling function of Zone 2. Zone 2 only controls whether to turn on or off based on temp setting.

I purchased two new Honeywell theromostats: RTH7600d and RTH6400d. The 6400d for zone two should be straightforward (R to R, Y to Y, W to W) - and I should just have to ignore the fan auto/on setting.

However, my issue is with the zone 1 tstat. I can't go 1:1 with the wiring, and honeywell told me that this tstat would work although I can't get them to respond to email or phone.

Can anyone help?

Thanks!

While the models you have listed are NOT listed to use with the Trol-A-Temp system if that is what you have they might be able to be made to work. You did not post which zone system you hae as far a model numbers are concerned so I could not look them all up. Who at Honeywell said they would work? Or did some salesman tell you they would work?

While the models you have listed are NOT listed to use with the Trol-A-Temp system if that is what you have they might be able to be made to work. You did not post which zone system you hae as far a model numbers are concerned so I could not look them all up. Who at Honeywell said they would work? Or did some salesman tell you they would work?

Hi! Carrier conventional gas forced hot air with A/C. No heat pump.

The control panel is an EWC ultrazone ewc-st-2d, pic attached. I am not worried about the 2nd zone control as the call for heat/cool *should be* fine with the smaller new honeywell.

The zone 2 tstat is wired R to R, W to W, Y to Y.

The zone 1 tstat is W to W, Y to Y, R to R, O to O, B to B, G to G.

Everything makes sense to me (G fan, etc) except the O and B.

On the other side of the panel, connecting the control board to the furnace, R is R and B is common. G to G, W to W, y to Y. O not used. My thoughts in looking at it now in-depth (and not before when I asked the question) is that if I wire the 7600d R to R, W to W, G to G, Y to Y, O to O and B to Common, ensure the setting on the honeywell is 170: 1 (heat/cool), 190 to 0, I may be all set?

The one thing I didn't do last night when I reverted back to old was to trace from the board to the furnace itself...

Let me know your thoughts? Greatly appreciate the help!

http://www.ewccontrols.com/acrobat/090377a0055.pdf

Main site for more info

EWC Controls (http://www.ewccontrols.com/)


YOU might read this since it does call for different part number Honeywell stats.

http://www.ewccontrols.com/acrobat/090375a0115.pdf

Sometimes have the right reference material can help. I believe you are headed in the correct direction..

Thanks for the links! I couldn't find it earlier.

OK here's where I'm at. I've successfully replaced the zone2 tstat with the new 6400.

Works fine if I leave the old Robertshaw 9610 in place. Cannot get the 7600 touchscreen to work - darn O and B wires - so I'll need to take it back and I guess find a professional grade one from a honeywell rep.

If anyone has any ideas let me know otherwise thanks for all of the help!

Just wanted to close the loop on this thread; there are only 4 models of tstats that work with my control board, and they are in the EWC page mentioned above.

I did speak with John at EWC and he informed me that there is one new tstat (the White-Rodgers 1f95-1271) that works with my panel.

FYI for anyone out there in a similar scenario.

All the best, and thanks again for all of your help! Was very helpful, and much appreciated!