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.
Not usually, but you need to put the wire in RC and leave RH empty.
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 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.
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.
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.
Yellow is the most common color for cooling wires, but Blue is also used in some systems. The cooling wire connects the thermostat to a compressor. Black (Or Blue) Wire is the so-called C wire or common wire. It is a 24V common wire that is linked to the transformer.
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.
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.
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.
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.
Note: If you have an R, Rc or Rh wire, you can put it into the R connector on the Nest Thermostat. If you have a W2, Y2 or O/B wire, you can put it into the *O/B connector, if needed.
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). You can also refer to the Conductor Color Chart (see Chart 6, thermostat wire).
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.
Look in the wall behind your thermostat base
As you examine the wiring, you will probably see two wire jackets, also called wire bundles. One of them, with Rc, G, and Y, comes from the cooling system. The other one, with Rh and W1, comes from the heating system.
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.
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.)
A 2-wire thermostat is almost always for a system with heat but without air conditioning, controlled by a digital thermostat. The two wires are most often red for power and white for heat.