Thermostat Wiring
September 8th, 2011
I have delusions of possibly making an embedded thermostat solution that tracks energy usage, inside and outside temperature and humidity and possibly online weather forecasts for setting house temperature. For this to work, I need to fully understand thermostat wiring. It took a bit of looking around the net to identify thermostat wire colors, thermostat terminals and functions, so I thought I would summarize it in a post.
| Label | Function | Wire Color |
|---|---|---|
| R | Power (24 VAC) | Red |
| RC | Power for Cooling | Red |
| RH | Power for Heating | Red |
| (RC and RH may be jumped together) | ||
| Y | Cooling Power to Compressor Relay | Yellow |
| Y2 | 2nd Stage Cooling Power | Varies (Lgt. Blue) |
| W | Heating (Gas, Oil, or Electric) | White |
| G | Indoor Blower Fan | Green |
| C | Common for 24 VAC Transformer | Black |
| O/B | Reversing Value for Heat Pump | |
| O | Energized in Cooling Mode | Orange |
| B | Energized in Heating Mode | Dark Blue or Blue (Rheem/Ruud) |
| E | Emergency Heat | Varies |
| X/Aux | Back up for Heat Pump or Aux Heating | Varies |
| S1-S2 | Shielded Outside Air Temp. Sensor | Varies |
All signals are 24 VAC from the R/RC/RH and C terminals. I need to research how much power can be pulled from this to run a device.
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