How do I install the Nest Learning Thermostat if my old thermostat had a short wire connecting Rh and Rc?
Unlike most thermostats, the Nest Learning Thermostat does not require a jumper wire between Rh and Rc. Nest knows that if you’ve heating and cooling and just one R wire, the power source is shared between them.
If your old thermostat had a wire between its Rh and Rc connectors (a wire that did not go into the wall), do not use this wire with the Nest Learning Thermostat. The Nest Thermostat's press connectors are built so that only one wire can be inserted per connector. The Nest Thermostat won't work if you insert jumper wires.
Instead of using jumper wires, the Nest Thermostat has an automatic internal jumper between the Rh and Rc connectors. Your Nest Learning Thermostat will activate this internal jumper if your system needs it. For example, if both an Rh and an RC wire are connected to the Nest Thermostat, the Nest Thermostat will not jumper these connectors together. But if the system has both heating and cooling and only one R wire, the Nest Thermostat will automatically jumper Rh and Rc.
Notice the short wire connecting Rh to Rc in the photo below. This is a jumper wire. If you have a jumper wire, discard it. Just connect all wires that come from the wall into their respective connectors on your Nest Learning Thermostat.
Your single R wire can go into either Rc or Rh on the Nest Thermostat.
Note: If you have separate heating and air conditioning systems, you might have separate Rh and Rc wires that come from the wall. These are not jumper wires, and you can insert the Rc wire into the Nest Thermostat's Rc push connector and the Rh wire into the Nest Thermostat's Rh push connector.