Cut Electricity to Thermostat

• 1). Turn off the breaker that controls electricity to your furnace or air conditioner.
  
  
• 2). Remove old thermostat from wall, using the screwdriver.
  
  
• 3). Unscrew the wires on the back of the old thermostat.
  
  

Prepare for New Thermostat

• 1). Check the screw placement on the back of the new thermostat to ensure that the old screws will work. If the old screws will not work, use a pencil to mark locations on the wall where new holes will need to be drilled.
  
  
• 2). Using a drill with a 3/16-inch diameter drill bit, drill holes in the wall where new screws need to go. The screws for your particular thermostat might differ in size, so check the exact size before drilling.
  
  
• 3). With the Phillips-head screwdriver, remove old screws and install new screws, leaving the heads slightly away from the wall. This will make it easier to slide the thermostat onto the screws after the electric has been hooked up.
  
  

Hooking Up the Main Power

• 1). Find the main red wire, using the flashlight, and attach it to the main power terminal on the thermostat. Do this by unscrewing the terminal slightly, then sliding the bare end of the wire into the hole behind the screw and tightening the screw against the wire. Repeat this procedure for the remainder of the wires. There should be three wires altogether: The hot (red) wire, the white wire and a green grounding wire.
  
  
• 2). Locate the red air-conditioning wire and screw it to the "RC" terminal on the thermostat. The wire are likely marked so you can differentiate the main wire from the heat and air-conditioning wires.
  
  
• 3). Look for the red heating wire and screw this wire to the "RH" terminal on the back of the thermostat.
  
  

Finalizing the Wiring

• 1). Locate the yellow wire and screw it to the "Y" terminal found on the back of the thermostat. This wire is for the compressor relay on the air conditioning. If your system has two cooling units, controlled by separate programs, find the light blue wire and screw it to the "Y2" terminal on your thermostat.
  
  
• 2). Find the white wire and screw it to the "W" terminal on your thermostat; this controls when the heat turns on and off. If your heater has a second zone, controlled by a separate program on the thermostat, there might be a brown wire. If so, screw it to the "W2" terminal on the electronic thermostat.
  
  
• 3). Look for the green wire, which is the fan relay wire, and screw it to the "G" terminal.
  
  
• 4). Locate the orange and dark blue wires, which will be present if you have a heat pump. Screw the orange to the "O" terminal, and screw the dark blue to the "B" terminal.
  
  
• 5). Find any wires left over, which are likely black and another color. Screw the black wire to the "C" terminal, which connects the thermostat to the transformer. The other wire, which has no universal color -- as noted on the website for high-performance HVAC -- and attach it to the "E" terminal, which stands for emergency heating and works as a back-up system.
  
  

Hanging and Setting the Thermostat

• 1). Hang the thermostat on the wall by sliding it over the screws you had left slightly sticking out from the wall. Now, slide the unit sideways so the screws lock into grooves on the back of the thermostat.
  
  
• 2). Reset the electric breaker for the heating and cooling system. Electricity is now restored.
  
  
• 3). Set the thermostat on/off times according to manufacturer's instructions; each unit is slightly different.