Replacing old for New Honeywell thermostat
RH &amp; RC are jumpered at the factory because most systems have only one transformer whether that is heating or cooling or both. If this is the case with your system, leave the jumper in place.  If you have a heating system combined with a cooling system and if both of those systems have their own transformer or if you have any two different system controlled by one thermostat and they have separate transformers then and only then do you pull the jumper.