Connect the R power conductor from the HVAC control transformer to the base plate terminal marked R. This conductor carries approximately 24V AC and supplies energy to the wall controller and system relays.
The cooling control line attaches to terminal Y, which activates the outdoor compressor contactor. Heating activation typically routes through terminal W, sending a signal to the furnace control board or heating relay. A separate conductor connected to G triggers the indoor blower motor.
If a dedicated common conductor exists, attach it to the C terminal. This path provides continuous return current from the transformer and stabilizes operation of the smart climate controller. Many installations lacking this conductor rely on intermittent charging through heating or cooling control lines.
Typical single-stage HVAC layouts use four or five conductors: red for 24V supply, yellow for compressor control, white for heating activation, green for fan relay, and blue or black as common. Matching these conductors to the correct base plate terminals prevents relay misfires and compressor short cycling.
Label each conductor before removal from the previous wall controller. Misplaced conductors can send a cooling signal during a heating call or leave the blower running continuously. Proper terminal mapping keeps furnace boards, compressor contactors, and fan relays operating in the intended sequence.
Nest Thermostat E Wiring Diagram With Terminal Labels for Heating Cooling and Fan
Attach the 24-volt supply conductor from the HVAC transformer to terminal R on the base plate. This conductor powers the wall climate controller and provides the voltage used to trigger heating, cooling, and fan relays within the HVAC equipment.
Route the compressor control line to terminal Y. When the controller calls for cooling, 24V travels through this conductor to the outdoor contactor coil, allowing the condenser compressor and fan assembly to start.
Heating and fan control terminals
Connect the furnace activation conductor to terminal W. A heating request sends voltage through this path to the furnace control board, which ignites the burner or activates electric heating elements depending on system type.
The indoor blower motor relay connects through terminal G. During cooling or manual fan operation, voltage on this terminal closes the blower relay and pushes conditioned air through the duct system.
Common conductor and power stability
Attach the return conductor from the HVAC transformer to terminal C. This conductor provides a steady electrical return path that keeps the internal battery charged and stabilizes electronic operation of the smart wall unit.
Typical conductor color mapping used in residential HVAC systems includes red for R, yellow for Y, white for W, green for G, and blue or black for C. Color standards may vary, so verify each conductor using the furnace control board labels.
Before mounting the device, photograph the original conductor placement on the previous wall controller. Incorrect placement may activate cooling during a heating request or keep the blower running without a call from the climate control system.
Identifying R Y W G and C terminals on Nest Thermostat E base plate
Locate terminal R first on the base plate. This terminal receives the 24-volt supply from the HVAC transformer. Without this conductor the wall climate controller cannot send control signals to heating, cooling, or blower components.
The cooling activation line attaches to terminal Y. When the device requests cooling, 24V travels through this conductor to the outdoor condenser contactor, energizing the compressor and condenser fan.
The heating control conductor connects to terminal W. A heating request applies low-voltage power through this terminal toward the furnace control board, which then activates gas ignition or electric heating elements.
The indoor air handler fan relay connects to terminal G. When voltage appears on this terminal, the blower motor begins circulating air through the duct network. Cooling calls usually energize both Y and G at the same time.
The common return conductor connects to terminal C. This path completes the 24-volt transformer loop and supplies continuous power to the wall controller electronics.
- R terminal – incoming 24V supply from transformer
- Y terminal – compressor control signal
- W terminal – furnace or heating relay trigger
- G terminal – blower fan activation
- C terminal – transformer return path
Typical residential conductor colors follow this pattern:
- Red conductor attached to R
- Yellow conductor attached to Y
- White conductor attached to W
- Green conductor attached to G
- Blue or black conductor attached to C
Verify conductor placement at the furnace control board before inserting them into the base plate. Matching both ends prevents incorrect signals such as compressor activation during heating calls or blower operation without a cooling request.