The component connected to the end of a damper motor shaft and used to verify that the combustion blower is on is the

• A. Pressure switch
• B. Flow switch
• C. Thermostat
• D. Limit switch

Answer: (A)

The main idea here is how a furnace verifies that the combustion blower is actually running. In gas furnaces, a pressure switch is used to confirm that the inducer or combustion blower has created the necessary draft in the vent. This switch is connected to the end of the damper motor shaft so that it only closes when the damper is in the correct position and the blower is producing the draft. When the inducer starts and creates negative pressure, the pressure switch energizes and signals the control that it’s safe to light the burners.

Flow switches detect air movement through a duct, but they’re not tied to the damper motor shaft to confirm blower operation. A thermostat determines temperature settings, and a limit switch acts as a safety cutoff for overheating rather than verifying blower status.