Latest revision as of 23:41, 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.
Red	Rc	Cooling Power	Provides 24VAC dedicated to the cooling control circuit (often jumpered to R in single-transformer systems).
Red	Rh	Heating Power	Provides 24VAC dedicated to the heating control circuit (often jumpered to R in single-transformer systems).
White	W/W1	Heat	Energizes the primary heating stage in conventional heating systems.
Yellow	Y/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/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/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.
+|-
+| Red || Rc || Cooling Power || Provides 24VAC dedicated to the cooling control circuit (often jumpered to R in single-transformer systems).
+|-
+| Red || Rh || Heating Power || Provides 24VAC dedicated to the heating control circuit (often jumpered to R in single-transformer systems).
+|-
+| White || W/W1 || Heat || Energizes the primary heating stage in conventional heating systems.
+|-
+| Yellow || Y/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/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/AUX || Auxiliary heat || Energizes the supplemental heating stage to operate in conjunction with the heat pump when additional heating capacity is required.
+|-
+|}