Heat Pump Thermostat Wiring - Air Conditioning Systems Heat pump thermostat wiring - A typical wire color and terminal diagram. As shown in the diagram, you will need to power up the thermostat and the 24V AC power is connected to the R and C terminals. The color of wire R is usually RED and C is BLACK. C is known as the common terminal. These two connections will ensure that there is power to the Heat Pump Thermostat Wiring Chart Diagram – HVAC Heat Pump Thermostat Wiring Chart. This is for use for heatpumps. You should 100% make sure that you have a heat pump system and not an air conditioner with electric heating strips as it is a common mistake for people to misidentify their HVAC systems.