What is the R-switch and how do I set it?

The R-switch controls how your R-wires are connected based on your system configuration. If you have 1 R-wire, set the switch to the up position and insert it into the R-terminal. If you have 2 R-wires, set the switch to the down position and insert the Rc wire into the Rc-terminal and the R or Rh wire into the R-terminal.