Rh and Rc Thermostat Wires Explained (Dual Transformer)

Rh is power from the heating transformer and Rc is power from the cooling transformer. If both terminals have their own wire from the wall, your home has two separate 24 V circuits, often a boiler plus a separate AC air handler.

Never connect Rh and Rc together on a system like this; tying two transformers together can damage the equipment. If there is only a short jumper between Rh and Rc and one wire from the wall, you have a single transformer: treat it as R.