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Early Prototypes

Basic Connection Points

TerminalColorDescription
C / XBlack24 Volt Common (Ground)
R / VRed24 Volt Transformer Power
RC / RHRed24 Volt Load for Cool / Heat
Y / Y1YellowSwitched Power for Cool
W / W1WhiteSwitched Power for Heat
GGreenSwitched Power for Fan

Heat Pump / Multi-Stage Connection Points

TerminalColorDescription
Y2can varySwitched Power for Cool 2nd Stage
W2can varySwitched Power for Heat 2nd Stage / Backup Heat
Ecan varyEmergency Heat (Heat Pump)
O / OBOrangeReversing valve (Heat Pump)