Dominate the HVAC Controls Challenge 26408-23 – Power Up Your Skills for 2026!

The main idea here is that the G terminal is the fan circuit. In a typical thermostat circuit, the thermostat can energize devices by sending 24 VAC from R to other terminals. When the thermostat calls for heating or cooling and the fan is commanded, the G connection completes a path to the indoor blower relay. Energizing G closes the blower relay in the furnace or air handler, which powers the indoor blower motor and pushes air through the ducts.

That’s why the indoor blower relay is the device connected to G. The other components aren’t controlled by G: the outdoor condenser is driven by the cooling call on Y, the defrost control is part of heat pump defrost logic, and the heat sequencer manages staged heating. So G is specifically for energizing the indoor fan.