Residential A/C Thermostat
Synopsis
Dave's quick reference on residential A/C systems. Use this information at your own risk.
Common Thermostat Wiring Colors
| Color | Code | Function | Description |
|---|---|---|---|
| Red | R | 24V AC Power | Supplies 24VAC from the transformer to the thermostat for control circuit operation. |
| White | W or W1 | Heat | Energizes the primary heating stage in conventional heating systems. |
| Yellow | Y or Y1 | Compressor | Energizes the compressor contactor to initiate cooling or heat pump operation. |
| Green | G | Fan | Energizes the indoor blower fan relay for air circulation. |
| Blue | C | Common | Completes the 24VAC control circuit by providing a return path to the transformer. |
| Orange or Brown | O or B | Heat Pump Reversing Valve | Energizes the reversing valve to switch the heat pump between heating and cooling modes. |
| Brown | E | Emergency Heat | Energizes the supplemental heating stage while simultaneously disabling the heat pump, forcing the system to operate solely on backup heat. |
| Blue | W2 or AUX | Auxiliary heat | Energizes the supplemental heating stage to operate in conjunction with the heat pump when additional heating capacity is required. |