Revision as of 23:39, 17 March 2026

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.

@@ Line 4: / Line 4: @@
 =Common Thermostat Wiring Colors=
+{| class=wikitable
+|+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.
+|-
+|}