Understanding Rh and Rc: What They Mean and Why They're Connected in Thermostats

 In a thermostat, the terminals labeled "Rh" and "Rc" are related to the control of heating and cooling systems, and they are connected to the respective power sources for these systems.

Rh (Red Heat)

• Rh stands for Red Heating. It is the terminal that connects to the power source for the heating system. The "R" typically represents the 24V power wire, which provides the necessary voltage to the thermostat.
• Function: Rh is used to control the heating side of the HVAC system.

Rc (Red Cooling)

• Rc stands for Red Cooling. It is the terminal that connects to the power source for the cooling system. Like Rh, Rc also carries 24V power but is specifically dedicated to the cooling system.
• Function: Rc is used to control the cooling side of the HVAC system.

Why are they Connected?

• In some HVAC systems, Rh and Rc are connected by a jumper wire or are internally linked within the thermostat because the heating and cooling systems use the same 24V power source.
• Single Transformer System: If your HVAC system uses a single transformer to power both heating and cooling, then Rh and Rc can be connected (or jumpered). This means that the same power source is being used for both functions, and the thermostat can control either system with the same power.
• Separate Transformers: In systems with separate transformers for heating and cooling, Rh and Rc remain separate to prevent mixing the two different power sources.

By connecting Rh and Rc, the thermostat can seamlessly switch between controlling heating and cooling systems using the same power source, making it versatile and compatible with various HVAC configurations.