Digital thermostats are much more precise and capable than analog thermostats; for example, digital thermostats can be set to bring on heat or cooling at an exact degree, and they can also be programmed to operate the system differently depending upon time or day of the week. While upgrading your thermostat may seem like a daunting task, it is actually simple as long as you work slowly and pay careful attention. Below is how to upgrade from a manual thermostat to a digital thermostat:
1. Disconnect the power to the heating and cooling system - Before beginning your work, it is important to turn off the electrical power to the system. The current levels at the thermostat rarely exceed 24 volts and are generally incapable of harming you, but damage to components could occur if you attempt to replace the thermostat while the system is powered. Shutting off the current will keep you from accidentally triggering startup of a component, and it will also prevent shorting of the thermostat or other system electronics. Turn off the power at the main breaker panel, and inform others that you will be performing work on the system.
2. Remove the analog thermostat faceplate - After power has been disconnected, pry the faceplate of the analog thermostat from the base plate mounted to the wall. You may need to use a flat-blade screwdriver to provide enough leverage to loosen the faceplate. Be careful not to gouge the wiring underneath if you need to use a screwdriver.
3. Take a photograph or diagram the wiring arrangement - Once the faceplate has been removed, you will immediately notice the presence of various colored wires leading to terminals. It is critical to record the wiring arrangement; failure to do so could result in accidental miswiring and damage to the system. Either take a snapshot with a digital camera or draw a diagram to identify wire locations. Be sure the photograph or drawing clearly identifies the color of each wire and to which terminal it is connected. Here is a list of commonly-encountered terminal identifiers and how they interact with the system:
W - This terminal connects to the system's heating element, or strip.
Y - The air conditioner compressor is controlled via a signal that passes through this terminal.
G - The terminal is connected to the blower fan located in the system's air handler unit.
O/B - Seen only on heat pump units, this terminal has a connection to the reversing switch inside the unit.
RC/RH - This consists of two terminals that are often connected together with a wire "jumper" and is the source of a constant 24 volts of power for all other components.
C - The system's common electrical connection, "live" wires leading from this terminal must never touch any other wires or terminals to avoid a destructive short circuit.
In many thermostats, the wire color will correspond to the letter code listed. For example, the 'W' terminal will be connected to a white wire, the 'G" terminal will be connected to a green wire and so forth. However, do not rely upon this color-coding alone, as this standard is not always adopted depending upon system age, manufacturer and even installer preference.
4. Remove the wires from the base plate and remove the base plate - After you have taken a photograph or created a sketch of the wiring terminals, remove the wires from the analog thermostat. They may be attached via screws or be pushed into position. Examine the ends of the wires to ensure they are not overly frayed or damaged. After removing the wires, unscrew the base plate from the wall and discard it.
5. Attach the base plate from the digital thermostat to the wall - Once the old base plate is out of the way, position the backside of the base plate for the digital thermostat in front of the wall opening. Drive screws through the mounting holes in the base plate into the drywall; tighten them carefully to avoid cracking the plastic material.
6. Connect the system wires to their appropriate terminals - Using the photograph taken or sketch drawn in Step 3, connect the wires leading from the system to the appropriate terminals inside the base plate. Be careful not to force the wires into position, and also be sure that you make tight connections between wire and terminal. Take another look at the photograph or sketch to verify that all wires are hooked up to the correct terminal and are not crossed or accidentally omitted.
7. Attach the faceplate of the digital thermostat - Once the new base plate has been attached and wired, push the faceplate of the digital unit onto the top of the base plate; push with firm, but gentle, pressure until the faceplate snaps into position.
If this is a process you don't feel comfortable doing on your own, reach out to an air conditioning contractor (click here for more information).