To change the speed of a belt-driven blower, what should a technician adjust?

To change the speed of a belt-driven blower, adjusting the blower wheel pulley is the appropriate action. This is because the pulley size on the blower directly affects the speed at which the blower motor drives the blower wheel. When the technician modifies the diameter of the pulley, it alters the ratio between the motor speed and the blower speed, which allows for a change in airflow without needing to replace the motor or make adjustments to electronic controls.

In contrast, modifying the blower motor speed setting typically applies to direct-drive applications where the motor speed is electronically controlled, while control board settings pertain to adjusting functions within the furnace that do not relate to mechanical components like pulleys. Additionally, thermostat settings influence the operation of the heating system but do not directly impact the blower speed, which is fundamentally tied to the physical components of the system. Therefore, adjusting the blower wheel pulley is the most effective and appropriate method to achieve the desired blower speed.