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Thermostat Terminal Designations Explanations - You are wiring a new thermostat or about to wire a new thermostat and you want to understand what the terminal designations are on your old and your new thermostat. Why is it such a mystery with these terminal designations? Once you get into seeing how this works it all becomes common sense. This is as long as whoever wired the thermostat originally followed the common sense code of designations.
A good example of this is I have opened thermostats and seen black used on the R terminal. Green used on the W terminal and red used on the Y terminal. Once you see the thermostat wire and the colors of thermostat wire that are available you will understand. As far as those unconventional wired thermostats I’ve seen, I can only think that the person was color blind. And that is giving them the benefit of the doubt. Now, on to the designations.
Here we will explain the designations and where they go and what they control. We will also reference another article about the colors for the thermostat designations. We get tons of emails and comments about this subject so we thought we would try to help you out. Hopefully, you will gain a better understanding of how your thermostat works by learning these thermostat terminal designations.
Thermostat Terminal Designations Explanations
First we start off with the thermostat terminal board itself. This is hidden away behind the actual thermostat and on a small plate referred to as the sub-base of the thermostat. It has little letters on it that differ from thermostat to thermostat but the most common designations are: R or RH and RC, G, Y, W, and C.
For heat pumps there are typically O and B terminals also. There are others and we will explain these as we go along here. What are these mystery terminals and where do they go and what do they control?
The List
Thermostat Terminal Designations - Conclusion
There other terminal designations in different thermostats from different manufacturers and the terminals are usually designated to control various things in the HVAC system such as a humidifier or an electronic air cleaner. Always read the owners manual and take photos of how the current thermostat is wired before undoing the wiring. Additionally, always turn the power off before touching the wires. First for safety and secondly because you can cause harm to the system by touching the wrong wires together. Hope this basic list of thermostat wiring terminal designations helps you.
Thermostat Terminal Designations