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

Adjusting the blower wheel pulley is the correct method for changing the speed of a belt-driven blower. The blower speed can be altered by changing the size or position of the pulleys in a belt drive system. Specifically, if the technician increases the diameter of the blower wheel pulley or changes the belt to a different configuration, this will change the rotational speed of the blower wheel itself.

The design of the pulley system allows for a mechanical advantage that can increase or decrease speed based on the tension and alignment of the belt. This method is efficient and maintains the performance and longevity of the motor and blower system.

In contrast, adjusting the blower speed setting typically applies to electronically controlled systems rather than mechanical ones like belt-driven systems. Changing the fan motor's voltage may affect the torque or power delivery but is not a standard method for controlling speed in belt-driven systems. Altering the air duct size would not directly affect the blower speed; instead, it would change the airflow and pressure dynamics within the HVAC system, which may lead to inefficiencies or imbalances.