The touchscreen control is the command center of the communicating HVAC system. Benefits of the communicating system are auto-configuration of the system, the ability to share information throughout the system for enhanced diagnostics and control, and simplified wiring. This ensures simple, reliable operation and an accurate installation.
Maybe this will save someone a headache. I have two thermostats side by side.
One heat- 2wire Honeywell analog thermostat. Oil furnace to baseboard.
One ComfortNet CTK01AA Thermostat 4wire. This runs my A/C. I wanted to combine both thermostats into one Nest. I purchased the Nest E and also the 3rd gen. Turns out the Nest will work with the Heat. But, not with the A/C.
Heat- two wires. Red- 24v power and white- boiler. Nest connections- red-red, white-white.
A/C Red- 24v power Blue- common Yellow- a/c White- fan? Inside the CTK0AA yellow-2 White-1 Nest hookup Red-red h Blue-blue Yellow-yellow White - green(fan) Btw- 3rd gen Rh & Rc - red heat & red cooling. So I used the 3rd gen to try to combine both thermostats. Only the 3rd gen can take two different power supplies. Nest powered up fine but the condensing unit would not turn on. The red wire still sent 24v power to the unit but it was a no go.
It seem this system is not a “legacy/traditional “ wired system. Power and common wires are normal but “ 1&2” wire are communication wires.
Not on/off relay style wiring. Traditional wiring would be - send voltage to fan on/off and the same to the air handler. The ComfortNet is a two-way communication system. Nest thermostats don’t work this way. I have read that the wiring can be redone to traditional standards but that is beyond my expertise. You lose diagnostic capabilities of the ComfortNet system.
I despise the cheap plastic ComfortNet thermostat and it’s lack of WiFi capability. So now I have the Nest E for heat and the CN thermostat for A/C side by side.
Very frustrating. I purchased both the 3rd gen Nest and also the Nest E. I first tried to install the Nest E. But, the Nest E only has one R connection.
For me to combine my separate heat and AC thermostats, I needed rh and rc (red heat and red cool). Both my systems have separate 24v power supplies. So, I bought the Gen 3 Nest. But, my AC still did not work. It was not until I learned the difference between legacy wiring and communication wiring that I figured out the nest is not compatible with my system.
My AC wiring is R,C,1,& 2. Some other legacy wirings are A,B,C & D. I can convert my system to traditional wiring but it is a bit complicated. I will try to link an article I found. I don’t believe Nest has any info on their website that differentiates between traditional wiring and communication wiring.
I spoke to a nest rep. (Hour long conversation) before I purchased the Gen 3. He said that it would work. I don’t believe the Nest reps are HVAC trained in any fashion.