Beating the Puzzle of Thermostat Wiring

Things You Should Know About Thermostat Wiring

Thermostat Wiring is a method of installing the thermo regulator in your house, office, car, or where else possible. It may be installed by yourself or by an electrician as you wish. Meanwhile, upon installation, the thermostat’s role is to primarily control the temperature by using its simple user interface with the internal workings of your home as well as its adjustable set point. It is used to regulate the desired temperature in a place. These are commonly used in no tropical places in America and in Southeast Asia to in order to ease the discomfort with the weather or climate. Usually, when the desired temperature is achieved, the systems get to be turned off while the expected temperature is delighted in.

Thermostat Wiring

Red C-24 V supply line from air conditioner transformer.

Red H-24 V supply line from Heat pump transformer.

White-To heat pump relay.

Yellow-To air conditioner relay.

Thermostat Wire
Color Codes

Source :

Rh Red 24 Volt Hot for Heating
Rc Red 24 Volt Hot for Cooling
Y1 Yellow First Stage Cooling
Y2 Blue Second Stage Cooling
G Green
Gray *
Energizes Indoor Fan
W1 White Energizes First Stage Heat
W2 Black Energizes Second Stage Heat
O Orange Heat Pump
Reversing Valve
Energized In Cooling
B Brown Heat Pump
Reversing Valve
Energized In Heating
C Brown** 24 Volt Neutral
(Common) leg

*     Found in some Carrier furnaces
**    The brown is often the first choice to use for the 24 volt common leg but white, black and blue are also used.


All of this goes out the window if the person before you didn’t know or care to use the accepted color codes. Sometimes it is simpler to take down the existing wiring and re-terminate using the accepted color codes than it would be to map a “creative” wiring scheme.

The most basic of systems only need 2 wiring for control. They bond to a 2-string thermoregulator. The terminals in the label that are commonly ‘R’ and ‘W’ usually work at 24V. The source of this control electric power results from a control electrical device fitted probably just away from, or through the chamber body. The line voltage feeding the heater is turned down to reliable level of 24 volts. Then, after making a series of loops through at least one safety device, the power goes up to the Thermostat Wirings. In exchange with the room temperature reaching the desirable set point, it triggers the contacts to close. Thus, completing the circuit to the gas valve allowing it to open, the main burner to ignite, and begin the cycle of heat production by the thermostat.

There are also some common types of thermostat wirings where you can be able to find 3 or more wirings. I commonly has terminal with the 3 wirings ‘R’, ‘W’, and ‘Y’. This model, when selected for cooling and when it reaches the point above the set-point, the thermostat will close the connection between the ‘R’ and the ‘Y’ terminal. This initial process shall trigger the wholeness of the machine to start the cooling process. This provides the cooling for the evaporator coils built in the machine.

For further reading you can see this

The Continuing Cycle

When the cycle starts, the temperature of the heat exchanger arises as the fan blower motor starts moving air through the heat exchanger and takes out the heat through the ducting in your home. If, for any reason, the fan fails to run, it will be normal but dangerous for the heat exchanger to get too hot. This triggers the hi-limit temperature device to open to the gas valve, closing the valve and stopping the heating cycle.

Through time, climate control systems have evolved considering that the demands from our generation have vastly arouse. Today, thermostat units are more efficient, and have more features to boast about. No wonder, that the use of the old Thermostat Wiring technology have been long forgotten by most. Meanwhile, some people still are fond of using the old technology, this is good when the technology works real good for them but in some cases of unnecessary damages or malfunction of the machine, the pieces that need to be replaced are most often unavailable in hardware stores, that may lead for them to get to either purchase another old model or adapt with the machine that the new tech has to offer.

Thermostat Settings

  • Set the air conditioner’s thermostat not lower than 78°F during summer months.

  • By winter, set it to 68°F. This will help you minimize energy costs or expenses.

  • When adjusting the temperature on the thermostat, do it gradually to ensure that every family member is comfortable with the adjustments, especially if you have toddlers or babies at home. You can do this by adding or reducing the temperature a degree at a time in a week.

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