What you will learn in the Thermostat Wiring Colors Code article:
First, what thermostat wire colors is likely to go to which terminal on the thermostat in your heating and cooling system
Secondly, the function of each wire terminal on the average thermostat highlighting some of the differences in those HVAC system functions from manufacturer to manufacturer as recommended for thermostat wire color
Always follow the thermostat manufacturer’s instructions whenever changing the thermostat. Always turn the power off at the air handler and the condenser and make sure there is no voltage at the transformer before proceeding.
Furthermore, the thermostat wire colors below are the most likely colors used for most installations; however, your thermostat wire colors may be different than what the indication is here. There is no official standard for thermostat wire colors. Additionally, thermostat wiring colors are not standardized. However, these are the most wiring methods used based on my years of experience in the HVAC field, where I successfully wired a lot of thermostats and as recommended by manufacturers and common sense for thermostat wiring colors code.
For instructions on how to wire a thermostat, please see how to wire a thermostat page. Refer back to this page for thermostat wire colors.
Before proceeding, we highly advise that you turn the power off at the circuit breaker. Furthermore, the power for both the condenser and the air handler/furnace. You may cause a dead short in the control circuit. Additionally, that could potentially cost you a service call for troubleshooting and repair.
Wiring Color Chart for Air Conditioners and Heat Pumps
Tracing a Wire to the Source
If you find the colors are not matching to the convention described here, you can always trace to the source. Furthermore, only if you are confident in your skills. Replacing an old thermostat with a new thermostat can be daunting so make sure to follow all thermostat wiring instructions. Lastly, follow the instructions on our How To Wire a Thermostat page for many great tips such as: Take a picture of the old thermostat wiring before you unwire it.
Remember, the wires coming from the thermostat are terminated in the HVAC equipment. Importantly, there is a high voltage inside the air handler, boiler, or other equipment where the wires terminate. Some HVAC system manufacturers provide a terminal strip board where the wiring is attached. Additionally, in different equipment, you will find a bundle of wires with wire nuts holding them together.
In either case, it is crucial to find the wiring diagram for the unit. Finally, this way, you can match up the appropriate wire color coming from the thermostat to what it controls in the equipment. The red wire should always come from the hot side of the 24-volt transformer. Additionally, the common (sometimes black) should come from the common side of the transformer.
Furthermore, the wire colors on the transformer will be different than the thermostat wires. If you do not know what you are doing, then please call a professional. Importantly, there are a few reasons for this:
First, as mentioned, there is high voltage in the equipment and can be hazardous to your health.
Lastly, if you wire it wrong or accidentally touch the wrong wires together, you can blow the transformer.
