A 4-wire thermostat wiring diagram is a representasion of how your thermostat utilizes four low voltage wires typically in a range of 24 volts, to manage the operation of your home’s heating, cooling and fan systems. Here we’ll go over the basics of each of the 4 common thermostat wires and their function.
4 Wire Thermostat Wiring Diagram
The 4 Most Common Thermostat Wiring Types Defined
Red Wire (R Terminal): The Red wire supplys 24 VAC power from the transformer to your thermostat. On most systems, the R terminal will be identified as either R, Rc or Rh. If your system has both Rc and Rh terminals they are allmost always jumpered to create an open path for power to reach your thermostat too.
White Wire (W Terminal): This wire is used to controll the heat source within your home. Your thermostat will connect the White wire to the R wire to activate your furnace or boiler to begin warming your home.
Yellow Wire (Y Terminal): The Yellow wire is used to operate the cooling component of your HVAC system; this includes the outside A/C compressor unit. When you need to cool your home down, the thermostat connects the R wire to the Y wire to enable the cooling cycle yet.
Green Wire (G Terminal): The Green wire operates the blower fan that circlates hot and cold air through your home when the fan is activated. When you want to simply circulate hot or cold air through your home the thermostat connects the R wire to the G wire.
How the 4-Wire HVAC System Works
In order for your thermostat to call for heating it creates a complete circuit between the R and W wires. In order to create a circuit for cooling, the thermostat will connect the R wire to the Y wire. To simply circulate hot or cold air through your home, the thermostat will connect the R wire to the G wire. This simple switching process enables your thermostat to control all three primary components of your HVAC system using only 4 wires.
Important Safety Consideratons
Before attempting to work with thermostat wiring ensure that power to your HVAC system has been turned off at the breaker. Prior to beginnning, take a picture of your current wiring configuration so that you may refer back to it should you need to. Never guess which wire is connected to wich, always confirm the terminal connection based upon the label located on your furnace control board. By adhering to these guidelines you can avoid damaging your system and minimize risk to yourself.
Get the PDF version of 4 Wire Thermostat Wiring Diagram here
