[PDF] 69-1714 - TH6110D Programmable Thermostat Installation The C (common wire) terminal is optional when thermostat is powered by batteries. W (O/B) terminal If thermostat is configured for a heat pump in the Installer Setup, configure changeover valve for cool (“O” factory setting) or heat (“B”). Wire specifications Use 18- to 22-gauge thermostat wire. Shielded cable is not required. Keep Heat Pump Thermostat Wiring Chart Diagram – HVAC Heat Pump Thermostat Wiring Chart Diagram - HVAC - The following graphics are meant as a guide only. Always follow manufacturers instructions for both the thermostat and the HVAC system. Additional articles on this site concerning thermostats and wiring can help you solve your problem or correctly wire a new thermostat.