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To effectively change the speed of a belt-driven blower, adjusting the motor pulley is the recommended action. By modifying the motor pulley size, the rotational speed at which the motor drives the belt can be altered. Since the blower's speed is directly related to the speed of the motor, changing the diameter or size of the motor pulley can lead to an increase or decrease in the air velocity produced by the blower.

In contrast, adjusting the blower wheel pulley could influence speed but is less common and may not provide the desired results. Simply changing the blower wheel would not be a practical solution for speed adjustments, as the wheel typically remains fixed in size and design unless there are specific requirements for a different airflow demand or a system redesign. Additionally, the motor pulley adjustment is generally more straightforward and efficient for speed regulation within a represented range of operation.