Thermostat Wire Color Code Guide

Whether you’re trying to fix your thermostat, or installing a new smart thermostat, this thermostat wire color code will help you to avoid DIY wiring problems. However, please note that this is a list of common wire colors used and your thermostat may contain different colored wires. If you have any doubts, get a professional thermostat installation.  

Below are the common thermostat wire colors:  

  • White wires 
  • Yellow wires 
  • Green wires 
  • Orange wires 
  • Red wires: Rc and Rh 
  • Blue or C wires

The White Wire

The white wire underneath your thermostat connects to your heating system. It terminates at your air handler or furnace. The white wire connects to terminal W in industry-standard thermostats. If your HVAC system has multiple heating stages, then you may find more than one white wire.

Yellow Wires

The yellow wires underneath your thermostat connect to your compressor. They control your air conditioning system. The yellow wires terminate at your compressor contactor via an air handler. The yellow wires connect to the Y terminals on your thermostat.

The Green Wire

The green wire underneath your thermostat connects to the fan of your furnace or air handler. It terminates at the air handler or furnace. The green wire connects to terminal G on your thermostat.

The Orange Wire

The orange thermostat wire links to your heat pump, if you have one. It terminates in your outdoor condenser for reversing valve operation from hot to cold. The orange wire connects to terminal O on your thermostat.

The orange wire only applies to homeowners with an air-source heat pump. Only air-source heat pumps connect to your outdoor condenser. Homeowners with geothermal heat pumps have no use for the orange wire.

Red Wires

Red wires indicate power. You may see an Rc and/or an Rh wire.  

The Rc Wire 

 Rc wires are for air conditioning systems or dual transformer systems. Dual transformer systems refer to a setup with a cooling and heating transformer. Rc wires connect to the RC terminals on your thermostat.

The Rh Wire

The Rh wire connects to your heating system as opposed to your cooling system. This wire may be red without an H attached to it, depending on if you have a dual transformer setup. The Rh wire connects to the RH terminal on your thermostat.

The Blue or C Wire

Blue wires are also called C wires because they are the Common wire. C wires are necessary for any smart thermostat that needs to be connected to a power source 24/7, regardless of your heat pump type. (It’s important to determine that your heat pump is compatible with your thermostat before you decide.) 

C wires or varying colors apply to every thermostat, but blue C wires belong to thermostats attached to a heat pump. Blue wires are for heat pumps. This wire connects to terminal B on your thermostat.

Got Your Wires Crossed?

There’s a lot to keep track of when it comes to thermostat wires! Avoid DIY wiring mistakes by calling Aire Serv® to help you get it right. We assist homeowners with thermostat installation and repair. Call (855) 679-0011 or request an appointment online to get started.

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