If your home has central heating, then your thermostat will usually be on the same circuit that powers your furnace and HVAC blower. If you only have central air conditioning, the thermostat and blower will typically be on one circuit and your outdoor AC unit will be on its own dedicated circuit.
In this case, there are two ways that you could notice a breaker switch for your HVAC system. The breaker switches will either be located in a breaker box in your garage or outside near the unit in a smaller metal box. Most of the time, there are multiple breaker switches.
You should always turn off the power before you connect or disconnect any wires from your Google Nest thermostat, and you should test to make sure that the power is off. This helps protect you and your equipment during installation or troubleshooting.
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.
Normally, the heater wires directly to the line voltage. The thermostat, on a separate circuit, connects to the breaker with another wire connected directly from the heating unit. If the thermostat is low voltage, relays or transformers may be required.
The thermostat is connected to your heating, ventilation, and air conditioning (HVAC) system, which draws its power from the electrical panel. Tripping a circuit breaker related to the HVAC system can result in a blank screen on the thermostat.
If your home has central heating, then your thermostat will usually be on the same circuit that powers your furnace and HVAC blower. If you only have central air conditioning, the thermostat and blower will typically be on one circuit and your outdoor AC unit will be on its own dedicated circuit.
A “No power” alert can be caused by the following: The thermostat wiring is incorrect. Your thermostat is connected to a system that requires a C or common wire, but that wire isn't connected. Some systems, including heat-only, cool-only, zone-controlled, and heat pump systems, require a C wire or Nest Power Connector.
While some people think the C wire is what powers the thermostat, this isn't entirely true. Typically, the "hot" wires, or the wires that provide power to the unit, are the heating and cooling wires, labeled Rc and Rh respectively. They provide the source of 24V power that comes into the main HVAC control board itself.
If you put wires into the wrong thermostat connectors during setup can, this can cause your system to malfunction or possibly damage it.
Yes, many smart thermostats are designed for DIY installation, and manufacturers typically provide step-by-step guides and videos. However, if your HVAC system is older or lacks proper wiring (like a C-wire), the installation might become more complex, and you may need professional help.
You can determine if the wiring is defective by turning the fan from the “Auto” setting to the “On” setting. The blower should start, which means your thermostat is getting power. Or, if the AC is on, turn the temperature down; if the furnace is on, turn the temperature up.
Most thermostat wires operate on 24-volt power provided by a transformer, and they are generally safe to work on without shutting off the circuit feeding the thermostat wiring. However, if the low voltage wires touch each other during the work, the system's internal fuse will blow.
Turn Off Power to the HVAC System
The first step in how to install a thermostat is making sure the power is turned off to your existing thermostat. Turn off the power for your heating and air conditioning system at the main service panel. Its circuit breaker should be clearly labeled.
Flip the circuit breaker that powers your thermostat to the 'off' position. Wait 30 seconds. Flip the circuit breaker back on. Switch the thermostat mode from 'off' to 'auto', 'fan', 'cool', or 'heat'.
Where Is My AC Circuit Breaker? Your AC circuit breaker will be included in the main distribution panel (commonly recognized as a gray metal box) in your garage, basement, or closet. You may also find the panel outside your house instead. Inside the box, locate the breaker switch marked AC or HVAC.
Red (R, RC, or RH): The red wire supplies 24V AC power to the thermostat. A wire labeled RH carries power to the heating system, while an RC wire provides a power connection between the thermostat and your cooling unit.
Short answer: yes, you should turn the power off to the indoor unit when changing a thermostat. If your thermostat has a common wire set up (C terminal, typically blue), then definitely yes, or you will stand a very good chance at blowing the low voltage fuse in the indoor unit.
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.
Power Supply
To check this, head to your home's circuit breaker. Since your thermostat is powered by your electrical system, the power switch can be found in your circuit breaker box. In the event your home loses power, that could trip your circuit breaker, resulting in a power loss to your thermostat.
To reset mechanical thermostats, simply turn off the thermostat and flip the circuit breaker. This can be done by going to the breaker panel and turning off the appropriate breaker switch for 30 seconds. After turning the breaker back on, turn the thermostat back on and the thermostat should be reset.
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.
HVAC components, however, are an exception in that a unit draws so much electrical power that it typically requires a dedicated breaker and does not share that circuit with other devices. Read on to learn about instances where this is the case.
A mismatched thermostat can damage the HVAC system and the electrical system. The clash between the instructions from the thermostat's computer algorithms with the HVAC system can harm components. (And if you add in a possible wiring error, things get even worse.)