I couldn't find any help on forums or websites if anyone may have tried to install Nest by replacing old Viconics P117 Board and E117 thermostat. I have an Electric Furnace and Heat Pump configuration. I have already brought the Nest 3rd generation and couldn't get it running. My system have only 3 wires connected in Thermostat(All other colour wire are note connected). I am adding the system diagram here so that you can look and suggest if I can make any wiring changes. Please help. Could only find manual in French. Final Configuration on Nest
It looks like the P117 + E117 was an intelligent system. Sort of like a NEST, but in 2 parts. This is different from the typical (in the US at least) thermostat where the thermostat - whether an old Honeywell dial, a typical digital setback thermostat, or a newfangled NEST - communicates to the HVAC equipment using a fairly standard set of wires. From the NEST manual:
- Heating: one, two, and three stages (W1, W2, W3)
- Cooling: one and two stages (Y1, Y2)
- Heat pump: with auxiliary and emergency heat (O/B, AUX, E)
- Fan (G)
- Power (C, RH, RC)
- Humidifier or dehumidifier (HUM, DEHUM)
You can actually see some of these wires in the P117/E117 diagram. For example, the upper right shows connections to C/X (the /X doesn't match NEST), R, G, W2; the right shows C, R, O/B, Y, W.
The problem is you can't just rip out the P117 and E117 and put in the NEST because you only have a 3-wire connection (which is all two computers need to talk to each other - equivalent to an old serial port send/receive/ground). You will likely need to find a way to run a new cable with more wires from the actual HVAC equipment directly to the NEST and then you can remove BOTH the P117 and E117.
Based on your comment that you already have a cable with the standard colors, you need to:
- Find and label all connections from your HVAC equipment to the P117.
- Replace all the connections from the P117 with the appropriate thermostat cable wires.
- Connect the NEST to the matching wires.
One critical piece is power. If I understand the diagram correctly, power is supplied on C/X and R in the upper right. The NEST needs power and that is listed as C, RH, RC. So C/X --> C and probably R to your choice of RH or RC. But I can't say for sure. The good news is that it looks like the C/X - R is 24V AC, which is standard for the US.
It appears your system does not support the Nest, and likely cannot
The P117 control board uses a proprietary protocol to talk to the thermostat, it appears. As it's the primary combustion control for your indoor unit, I would hesitate before throwing it out -- it may be the case that your system is not compatible with more "generic" furnace or boiler controls, even. Or in other words, the Nest may have to go, because the P117 board can't.