new thermostat install problem

Put the Red on R/RC, cap the blue, and remove one of the fan speed wires. You only want one fan speed at a time. If you want to have both speeds available, install a small single pole double throw switch on the side of the thermostat housing which you would then select manually and the thermostat would turn it on and off.(You only need small wire for the fan as the thermostat should be controlling relays.)

If you can find a thermostat with a fan speed switch built in you wouldn't have to add the switch. I have seen them but couldn't find one locally when I changed ours.