It alters the heat pump cycle from heating to cooling and vice versa.

This portion of the heat pump changes the direction of the refrigerant flow. The reversing valve in a heat pump system connects to the O & B terminals. The installer could have used any color, though. It’s usually black, but in some cases, it’s the thermostat blue wire. The common wire doesn’t have a standard color. This particular wire extends from the transformer and is responsible for completing the 24 V power circuit in the thermostat. This wire is responsible for triggering the blower fan. When you’re looking at your thermostat wire colors, you’ll notice a green wire connected from the fan. It enables the thermostat to control the air conditioning unit. The wire that connects to the Y terminal is yellow and connects to the compressor in your cooling system. It connects directly to the furnace, boiler or other heating source and is generally white. The W terminal the one that triggers the heating. You could install a jumper in between the RH and RC terminals if your system only has one transformer. This means you’ll have more wires to connect when you change your thermostat. Its wiring is slightly more complicated because it requires more circuits to work properly. The heat pump system setup differs from a standard unit. More than likely, your heating, ventilation and air conditioning (HVAC) consists of an oil, gas or electric furnace and an air conditioning unit.Īlthough this is the setup in a majority of homes, some homes have a heat pump system. It gives you a general idea of where the wires go in case your model doesn’t connect the way explained in this article. It’s highly recommended that you use at least one of the tips mentioned above before you disconnect and replace the thermostat.

You may want to mark the terminal where each wire connected.Ī majority of modern smart/ wifi thermostats have stickers, so you’re able to label the old thermostat wires before you remove it. You want to take a photo of the current wiring because even when you have your old device removed, you’ll still have a map of how the wires were connected to the base. You’ll have a map of exactly where the wiring was connected to the base. Tips for Changing a Thermostatīefore you uninstall the old thermostat, take a picture of its wiring to act like a thermostat wiring diagram. Keep in mind, the person who installed your thermostat may not have followed the same procedure, so your system might not match what’s going to be explained in this article.

3 wire AC transformer color codes