nest Learning - Conventional Wiring Diagrams; 1 & 2 Stage Heating Diagrams

Wiring Diagrams: Conventional Heating/Cooling Systems
Conventional 1 Stage Heating

Label:
Function:

Y1
Compressor Relay (Stage 1)
Y2
Compressor Relay (Stage 2), 2nd-speed fan
relay
G
Fan Relay*
O/B
Heat Pump Changeover Valve
Rc
24VAC power from cooling transformer
W1
Heat Relay (Stage 1)
W2/AUX
Heat Relay (Stage 2) / Auxiliary Heat Relay
C
24VAC Common Wire †
*
Star: W3, E, HUM/DHUM, 3rd-speed fan relay
Rh
24VAC power from heating transformer ‡


Conventional 2 Stage Heating

Label:
Function:

Y1
Compressor Relay (Stage 1)
Y2
Compressor Relay (Stage 2), 2nd-speed fan
relay
G
Fan Relay*
O/B
Heat Pump Changeover Valve
Rc
24VAC power from cooling transformer
W1
Heat Relay (Stage 1)
W2/AUX
Heat Relay (Stage 2) / Auxiliary Heat Relay
C
24VAC Common Wire †
*
Star: W3, E, HUM/DHUM, 3rd-speed fan relay
Rh
24VAC power from heating transformer ‡

* Fan relay (G) is optional. However, without a G wire, Nest will not be able to control the fan independent of heating.
† Common wire (C) not required in most cases, but strongly recommended.
‡ Use Rh or Rc in single transformer systems; no jumper wire required. For dual transformer systems, use Rh for the heating
transformer and Rc for the cooling transformer
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