When the fan on function is selected at the thermostat, which terminals does the switch close between?

When the fan on function is selected at the thermostat, the switch closes between the R and G terminals. The R terminal represents the power supply, typically providing 24 volts, while the G terminal is connected to the fan relay. When the fan on setting is activated, a circuit is completed between these two terminals, signaling the fan to operate independently of the heating or cooling functions. This allows the user to run the fan continuously or as needed for air circulation.

It's important to note that the W terminal is usually associated with heating systems, and closing it might engage the heating element rather than the fan. Similarly, the C terminal serves as a common return for the system, and while it is relevant in the context of powering devices, it does not directly control the fan operation in the scenario described. Therefore, understanding which terminals are involved helps clarify how thermostat settings influence system operations.