Wires and stuff

Wires and stuff

Rh, Rc - Power Wire
Y1 - Compressor (for AC and heat pumps)
Y2 - 2nd Stage Compressor (for AC and heat pumps)
W1 - 1st stage of heating, alternate heat or auxiliary
W2/AUX - 2nd stage of heating, alternate heat, or aux
O/B - changeover valve
C - common wire
G - fan wire
*  - star connector
(W3) Third stage of heating
Emergency Heat
Humidifier
Dehumidifer

	 order on
	   backplate
 ——————————
/				      \
|    Y1	     W1		|
|    Y2	     W2/AUX	|
|    G		     C			|
|    O/B	     *			|
|    Rc	     Rh		|
 \				       /
 / ——————————\

R wires = PoweR
Usually red
Usually only one
Rh = heat
Rc = cooling
Normally only need one
Rc/Rh - 24VAC power from cooling transformer
You don’t need jumper wires from Rh->Rc
Nest automatically jumps connectors when needed

W wires = heat
Usually white
W1 = first stage heating
W2 = second stage heating
W3 = third stage heating
Emergency heat (heat pump), goes to * connector
Can act as AUX heat

Y wires = compressor
Usually yellow
1st stage (Y1), 2nd stage (Y2)
Heat pumps also use compressors

G wires = Fan control
Usually green

O/B wire = changeover control for reverse valve
Usually orange
Used by heat pumps
AKA  Heat changeover valve, reversing valve
Can also be “dampers"
Can go into either O, or B terminal potentially
O defaults to heat

C wires = common wire
Usually blue
24V AC
Referred to as common ground wire
Helps keep the battery charged

Star connector
Can be used for:
W3 - Stage 3 Heat
E - Emergency Heat
HUM - Humidifier
DEHUM - Dehumidifier
no specific color



Compatibility And Such

(95% of low voltage market)

Works out of the box with following setups:
Heating: one, two, three stages (W1, W2, W3)
Cooling: One and Two stages (Y1, Y2)
Heat pump: auxiliary and emergency heat (O/B, AUX, E)
Humidifier or dehumidifier (HUM, DEHUM)
Fan (G)
Power (C, Rh, Rc)
R, Rh, Rc, W1, W2/Aux, Y1, Y2, O/B, C, G
* = W3, or E (emergency heat), or HUM or DEHUM

Pro setup can make Nest work with:
Dual fuel systems
Heat Pump
Plus furnace
More complex systems
Humidifiers
Dehumidifiers

Humidifier, Dehumidifiers…
Single wire humidifiers/dehumidifiers are controlled by the * connector
Two wire systems might require additional parts (relay)
Must be configured in Nest’s Pro Setup
Requires a professional to assess the specific requirements of the system

Incompatible Systems

Nest is NOT compatible with:
Remote or Floor sensors (S) < 1%
Proprietary Systems < 1%
Milivolt systems

Incompatible Wiring

Nest is NOT compatible with:
Three stage cooling
No Y3 terminal
Systems outside of the USA and Canada
Stranded Wires

knowledge base Incompatible-HVAC-Systems

Other Connectors

X2 - Could be either AUX Heat or a Common Wire. Check the old thermostat’s manual to determine it’s functions.

Unused Wires

S1 and S2 - These are sensor wires used to determine the outside temperature. Nest doesn’t support sensors and uses weather data from Weather Underground when connected to Wi-Fi

L - Service level alert for Heat Pumps. Nest doesn’t support Service Indicator (L) wires. Nest can control heat pump heating and cooling without this wire.

Duel Labeled Thermostats

Many thermostats work with conventional and heat pump systems.

Some thermostats have two rows of wire labels, or have two labels listed side by side.

Label lists a second letter for use with heat pump or conventional systems.

Example
Conventional:
	W = Heat, Y = A/C Compressor

Heat Pump:
	B = Changeover valve, Y = Compressor


Jumpers

Nest knows if you have just one R wire

Dual labeled thermostats have jumper joining R and Rc, Nest shares power between the two terminals.

Wiring Configurations