Google Nest Learning Thermostat 4th Gen Installation And Configuration Manual page 25

Conventional Connectors
Stage 1 compressor
Y1
relay
Stage 2 compressor
Y2 relay, 2nd-speed fan
relay
G
Fan relay
O/B Not used
24VAC power from
Rc
cooling transformer*
W1 Stage 1 heat relay
W2/AUX Stage 2 heat relay
24VAC Common wire
C
Stage 3 heat (W3),
humidification (HUM),
dehumidification
Star*
(DEHUM), 3rd speed fan
relay
24VAC power from
Rh heating transformer
Humidification (HUM),
AQ+ dehumidification
(DEHUM), or ventilation
* No jumper wires required. You don't need to hang on to any old jumper wires going from Rh (sometimes just
called R) to Rc. Nest will automatically jump these two connectors.
Second wire from
AQ- equipment in AQ+ (if
applicable)
Heat Pump with Aux
Heat Connectors
Stage 1 compressor
Y1
relay
Stage 2 compressor
Y2
relay
G
Fan relay
Changeover valve
O/B
relay
24VAC power from
Rc
cooling transformer
W1 Not used
W2/AUX Auxiliary heat relay
C 24VAC Common wire
Emergency heat (E),
humidification (HUM),
Star*
dehumidification
(DEHUM)
24VAC power from
Rh
heating transformer
Humidification (HUM),
dehumidification
AQ+
(DEHUM), or
ventilation
Second wire from
AQ- equipment in AQ+ (if
applicable)
Installation Overview - Terminal Overview
Heat Pump with Dual
Fuel Connectors
Stage 1 compressor
Y1
relay
Stage 2 compressor
Y2
relay
G
Fan relay
O/B Changeover valve relay
24VAC power from
Rc
cooling transformer
W1 Stage 1 heat relay
W2/AUX Stage 2 heat relay
C 24VAC Common wire
Emergency heat (E),
humidification (HUM),
Star*
dehumidification
(DEHUM)
24VAC power from
Rh
heating transformer
Humidification (HUM),
AQ+ dehumidification
(DEHUM), or ventilation
Second wire from
AQ- equipment in AQ+ (if
applicable)
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