I only have 4 wires for a 5 wire thermostat! If it isn’t, and you want a C-wire for continuous power to the thermostat, then you probably need the service of an HVAC technician. Put the cover back on, and see if the display is lit up. Try this next: Remove the blue wire from the C terminal, and connect the black wire to it. If so, you have effectively installed a C-wire. Now, is the digital display on the thermostat lit all the time? I Try this first: Pull the blue wire out of the bundle.

The purpose of the upgrade is to add a C-wire. Usually, the extra wires are twisted together, not connected to anything, and “stuffed” into the thermostat opening in the wall. This means that if you have a 4 wire thermostat, you very likely have extra wires. Most thermostat wiring is a bundle of 6, 8 or 10 wires. Or you can use only 4 wires with a 5 wire thermostat.ġ). You can upgrade a 4 wire to 5 wire thermostat by adding a C-wire. Rheem and Ruud owners – a dark blue wire is connected to the O terminal instead of an orange wire. The orange wire connects to the O terminal and operates the reversing valve in the heat pump, so that it delivers heat in winter and removes heat in summer. Yellow to Y Green to G Red to R Blue or Black to C Orange to O. Heat pump 5 wire thermostat color code: A heat pump and air handler system uses the following thermostat terminals and colors. Color wire isn’t important, other than to have a uniform color code, as long as the wire is attached to the corresponding terminal in the thermostat and on the control board of the furnace. In some thermostats, a black wire is used for the common wire. Without a common wire, the thermostat only draws power from the furnace when the system needs to start a Heat or Cool cycle. As a result, it provides continuous 24V power to the thermostat, so that the digital display is always on. A common wire creates a loop with the red wire/R terminal.

What is a common wire? It’s also called the C-wire. This wire and terminal power the furnace fan, aka blower. As with W, a 2-stage AC thermostat has Y and Y2.

Yellow wire to the Y terminal for 1 stage air conditioning.

A transformer in the furnace sends 24 volt power to the thermostat for its power as needed, not continuously. Your furnace is either 110-120 volt (gas and oil furnaces) or 220-240 volt (electric furnaces).

Red wire to the R terminal for 24 volt power.When only one W terminal is found, instead of W and W2, it indicates one-stage heating. White wire to the W terminal is for heating.And the color code for a heat pump follows. While the diagram color code is clear and straightforward, a brief explanation of the colors and terminals could be useful for some readers.

Ac transformer wire color code