An airflow control system for a blower providing the combustion air for an HVAC system comprises a single phase AC blower motor driving a blower wheel within a blower housing, a vacuum sensor mounted to the housing to sense the vacuum or pressure differential created by the blower as it operates, and a controller that receives as its only feedback signal a variable signal from the vacuum sensor which signal is proportional to the sensed vacuum within the housing and provides an output voltage to the blower motor to adjust the blower motor speed to thereby preferably produce a constant air flow.