The voltage from terminal G to the load side of the transformer (thermostat closed, fan auto) is:

The voltage from terminal G to the load side of the transformer (thermostat closed, fan auto) is:

• A. 6 V
• B. 12 V
• C. 24 V
• D. 48 V

Answer: (C)

The thermostat control circuit for a blower runs on 24-volt AC. The G terminal is the fan relay input, and the transformer’s secondary provides 24 VAC to the thermostat and related control circuits. When the thermostat calls for fan (thermostat closed), it completes the circuit between the transformer and the G input, so the blower relay coil on the load side is energized with the transformer's 24 VAC. That’s why the voltage from G to the load side is 24 V in this scenario. Other voltages (6, 12, 48 V) aren’t used for standard thermostat fan control, and wouldn’t properly energize the blower coil.

The thermostat control circuit for a blower runs on 24-volt AC. The G terminal is the fan relay input, and the transformer’s secondary provides 24 VAC to the thermostat and related control circuits. When the thermostat calls for fan (thermostat closed), it completes the circuit between the transformer and the G input, so the blower relay coil on the load side is energized with the transformer's 24 VAC. That’s why the voltage from G to the load side is 24 V in this scenario. Other voltages (6, 12, 48 V) aren’t used for standard thermostat fan control, and wouldn’t properly energize the blower coil.