How to Wire a Rheem and Ruud Thermostat

Disconnect the power to your heating and cooling system at the breaker or the fuse panel.

Use a voltmeter to ensure that there is no power flowing to the thermostat before you begin working on it.

Remove the cover of the existing thermostat and label the wires before disconnecting them. Tag each wire with a piece of tape or draw a diagram of the wiring with their respective labels on a piece of paper.

Connect the red return wire labeled "R," "VR-R" or "V-VR" to the terminal labeled “R” on the Rheem and Ruud thermostat.

Attach the stage one heating and cooling circuit wire, labeled "Y," "Y1" or "M" to the terminal labeled “Y” on the new thermostat. This wire is typically yellow.

Find the orange reversing valve wire or cooling wire, which may be labeled as "O" or "R," and connect it to the Rheem and Ruud thermostat terminal labeled “O.” In some thermostats this wire may also be blue.

Connect the reversing valve wire for the heating mode, labeled "B" in both circuits. Not all systems and thermostats have this wire. If yours does not, then cap it with a wire nut.

Attach the green fan control relay wire, typically labeled either "F" or "G," to the terminal labeled "G" on the new thermostat. This wire operates the furnace fan blower and is on most thermostats.

Connect the second stage cooling circuit wires that should be labeled as "Y2" on both wiring circuits. This wire may be blue or pink, depending on the existing thermostat model. The second stage heating circuit may be labeled as "W1," "W2" or "W-U" and is usually a pink wire. Connect this to the thermostat terminal labeled as "W2" on the Ruud and Rheem thermostat

Attach the LED system monitor wire, which may be labeled “X,” to the terminal labeled "L" on the new thermostat. These wires are typically blue, brown, tan or gray.

Connect the emergency heating circuit wire to the thermostat. This is usually always labeled “E”. Depending on the model of thermostat, these wires may be blue, pink, gray or tan. This wire is not always used; but when it is connected, it is constantly active.

Attach the blue, brown or black 24-volt transformer common wire, which may be labeled as "C," "X" or "B" on the old circuit, to the terminal labeled "C" on the Rheem and Ruud thermostat.

Install the new thermostat cover and turn on the power to the HVAC system to test the thermostat. If it does not switch on or some of the functions do not work properly, turn off the power and check your wiring. It may be necessary to contact an electrician to check your main electrical circuit.