Which wires are used to check the fan circuit?

To check the fan circuit, the R and G wires are utilized. The "R" wire, or 24V power supply, is the common connection for the thermostat. The "G" wire is specifically designated for the fan relay in the system. When you connect the R and G wires, it signals the fan to turn on, thereby allowing the technician to verify that the fan circuit is functioning properly.

Understanding the role of these wires is crucial within HVAC systems. The R wire provides the necessary voltage, while the G wire controls the operation of the fan. This simple connection is a practical method to ensure that the fan circuit is operational without the need for additional controls or components.

Using R with other wires such as W, Y, or another R won't engage the fan circuit as effectively or at all, which is why they aren't suitable for this particular check.