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.
The placement of the R wire, also known as the power or 24-volt wire, depends on the specific HVAC system and thermostat setup. In most cases, the R wire is connected to either the RC (cooling) terminal or the RH (heating) terminal on the thermostat.
With dual-transformer systems you'll have two R wires—one from the cooling transformer (Rc) and one from the heating transformer (Rh). Learn how to install an ecobee thermostat in a dual-transformer system. If you don't have an Rh wire, Rc serves as both the cooling and heating power wire.
If you only have one R wire (no Rh or Rc), you can connect your R wire to either Rc or Rh on the Nest thermostat. Important: Don't connect any Jumper wires to the Nest thermostat. If you don't have an Rc wire, the Rh wire is the power wire for both your heating and cooling systems.
There is no standard for the color of the RH wire, but most units use a red one. The RC wire, on the other hand, refers to “red cooling”. It's the same with the RH wire in that it powers the thermostat. For the RC, it powers the cooling system.
If you have two wires, R or RH go into the R terminal and RC into the RC terminal. If you have more than one wire (for example, you have a wire labeled R and another wire labeled Rc), remove any jumpers between the R and Rc terminals or push the switch to open the RC terminal to insert a wire.
This is the most typical thermostat wiring style, and it applies to systems that regulate both heat and air conditioning. The wires are typically arranged as follows: red for 24-volt hot, white for heat, yellow for cooling, green for the fan, and blue for common (although the common wire may be a different color).
This means that the wire isn't sending voltage to your thermostat. Some wires, like a C or R wire, need to send voltage to keep your thermostat powered on. If all the wires are grey, the system may be powered off or experiencing some other power-related issue.
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.
With a Nest Thermostat E or Nest Learning Thermostat, you'll need to install a C wire if the thermostat has power issues or its battery often drains.
They are normally connected together. If a system has 2 separate transformers , one for heating and one for cooling R is the heat power and RC is the cool power.
18-gauge and 20-gauge wires are generally recommended for thermostat wiring. Smaller gauge wire is appropriate for thermostat wiring because this wiring generally carries a very limited amount of power which makes it suitable for low-voltage applications.
So apparently Nest Thermostats need 5 wires to work correctly. It doesn't tell you that when you buy it. The 5th wire is the wire that charges the battery back up….
HVAC-R stands for heating, ventilation, air conditioning and refrigeration.
One of the most common reasons why a thermostat may fail to turn on the air conditioning system is dead batteries. If the batteries in your thermostat have died, it may not have enough power to communicate with the air conditioning system and turn it on.
The common wire, sometimes referred to as the c-wire, is what's responsible for delivering constant power to your thermostat. For programmable and smart thermostats, c-wires are required for setting a heating or cooling schedule.
"Rh"(R-Heating)&"Rc"(R-Cooling) are used separately if you have separate heating system and separate cooling system on one thermostat.
A bad transformer or bad wiring can also cause your thermostat to go blank. Another possibility is simply that the thermostat is broken and needs replacing. All thermostats reach the end of their lifespan at some point. If yours is an older one, it's a good idea to replace it with a programmable one.
If your thermostat doesn't detect a wire, or has a power issue, you should check that the wire end is straight, fully inserted into the wire connector, and isn't corroded.
If you wire a thermostat wrong, you may damage the thermostat, the electrical system, or the HVAC unit itself, which makes the entire installation process more frustrating. You may find yourself testing thermostat wires for hours, trying to get them right.
RC: The RC terminal is the 24-volt cooling power supply. RH: The RH terminal is the 24-volt heating power supply. (Note: The RC and RH terminals are jumpered together in a four-wire heat/cool system and a single-stage heat pump system but not in a five-wire heating/cooling system.)