Unlike most thermostats, the Nest Learning Thermostat does not require a jumper wire between Rh and Rc. Nest knows that if you’ve got heating and cooling, . If a problem with your wiring is detected, your thermostat will display a . The Nest thermostat isn’t physically detecting your Rc or Rh wire or one isn’t attached. The R wire is the power wire for your heating and cooling 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. Do not connect any Jumper wires to the Nest thermostat. If the air conditioning thermostat has one transformer to power both the heating and cooling system, then the wire from the transformer goes directly to the RC terminal and is called the RC wire. Effectively there isn’t a second RH wire, although there is an RH terminal. There is an exception, specifically if you have the Lyric Round Wi-Fi Thermostat. That can be used without a C-wire in most instances. However, if you plan to . The Nest thermostat isn’t physically detecting your Rc or Rh wire or one isn’t attached. Or power wires are physically detected, but the Nest thermostat isn’t .