Rc and Rh: The red wire(s) are the power source for your thermostat. If your thermostat is dedicated to air conditioning only, it will have a red Rc wire. For heating and cooling systems, it will have a red Rc and a red Rh wire. Though both wires are red, they are not interchangeable.
While batteries are used to power several thermostat models, some get their power by the 24 volts from the transformer. This is located in your HVAC equipment.
They didn't need their own dedicated power supply. But, in this new age of heightened technology, smart homes, and fancy touchscreen displays your thermostat needs a constant source of power. How does it get this power? The thermostat C wire, or common wire, enables power to continuously flow power to the thermostat.
#1 Option – Do Nothing At All – The good news is that all smart thermostats don't require a C-wire. Some can work equally well without them. However, the claim is slightly misleading because, in these cases, the thermostat draws the necessary power for its screen and Wi-Fi capabilities by stealing power.
Check the circuit breaker panel.
The next simplest solution for a thermostat that has no power is a tripped circuit breaker. This is a common cause for appliances, power outlets, and HVAC equipment not working. Open your electrical panel and look for a switch that is not aligned with the rest.
Place the multimeter's red probe onto the thermostat terminal marked R for red; you can place the black probe onto any of the other terminals. The multimeter reading should be at or close to the thermostat's voltage level.
Check the Circuit Breaker
If it's tripped, reset it by flipping the switch off and then back on. However, if the breaker trips again immediately or after a short period, this could indicate a deeper electrical issue, such as a short circuit in the wiring or an overloaded circuit.
Without a C-wire, a smart thermostat may disrupt Wi-Fi connectivity to other devices or can cause the HVAC system to cycle continuously, which puts more strain on the system and can lead to damage.
In an HVAC system, the transformer is typically located inside your furnace, but it may be located in your outdoor AC unit in some cases.
A "C" wire is the common wire that completes the electrical circuit from your transformer to your thermostat. "R" and "C" complete the 24v AC circuit to power the smart thermostat. Older "dumb" thermostats don't need power to operate things like wifi.
Yes, the thermostat stores the set point and schedule. When power is lost to the thermostat, the only information it "loses" is the current time. Once power is restored, the thermostat will resume its previous settings and configuration.
Like everything in your home that runs on electricity, the thermostat is connected to a switch in your home's circuit breaker. The system will automatically shut down if the circuit supplying electricity to your thermostat gets overloaded. The circuit will flip to the Off position.
Most digital thermostats are both hardwired to your house and have backup batteries. The reason for having backup batteries is to save any programmed information. Knowing what to expect when batteries are low or changing them annually can help you take care of your HVAC system.
A C wire, connected to C on the equipment, is required for the thermostat to power itself. Verify the furnace / air handler door is closed, the power switch is on, and the breakers are on. Confirm you have a C wire in the C terminal.
The HVAC control board is where the thermostat wires connect to your heating and cooling system. In most cases the control board can be found at your furnace or air handler.
Each thermostat will have a sensor inside that measures temperature via infrared radiation. This is a specific type of electromagnetic radiation that the human eye cannot detect. These air conditioner temperature sensors will scan the infrared radiation around them and convert it into electrical signals.
Locate the Common Wire
Look for a wire connected to a terminal labeled with a “C” on the thermostat. If you have one, that's your c-wire, and you're ready for general installation. The common wire, sometimes referred to as the c-wire, is what's responsible for delivering constant power to your thermostat.
Some instances may require both a relay and transformer. Do not use more than four relays without a transformer for one thermostat.
If you get a “The C wire isn't getting power” error code during power test, turn off your HVAC power at the circuit breaker. Remove the thermostat display and make sure that the C wire is fully inserted then turn the power back on. If the C wire still isn't getting power, we recommend contacting a Pro.
If there is no hidden C-wire, you can use a G-wire instead. However, you will not be able to use your fan independently when the heating or cooling isn't running.
In this case, you'll want to check for the following: Tripped Circuit Breaker: The main issue here is not with the thermostat itself but with the electrical panel. Go to the breaker panel and locate the circuit breaker for your thermostat. If it's off, try to reset the breaker switch.
Check your breaker box for a blown breaker or tripped fuse. You may be able to fix this AC issue with the flip of a switch. If that doesn't do the trick, check the wiring in your thermostat. A loose or frayed wire could also prevent your unit from turning on.
A blown fuse inside your thermostat will cause the device to malfunction. You'll need to open the panel and locate the fuse. This is a small, clear cylinder with metal ends and a filament running through the center. If this filament brakes, the fuse has blown and will need replacing.