This prevents the furnace from running with blocked vents or a failing blower, which could lead to dangerous carbon monoxide buildup. If the switch does not register the correct pressure within a few seconds of the fan starting, it signals the control board to halt the ignition process.
Furnace Pressure Switch Inspection Tips: Key Checks and Solutions
Testing the Pressure Switch with a Multimeter The most reliable way to determine if a pressure switch is faulty is to test it with a multimeter. Required Tools and Materials Multimeter (digital or analog) Screwdriver set (flathead and Phillips) Vacuum cleaner with a small brush attachment Manometer (optional, for advanced diagnostics) Replacement switch (if testing confirms failure) Visual Inspection of the Switch and Venting Begin by conducting a visual inspection of the pressure switch and its connection.
Also, examine the venting outside your home to ensure it is not clogged with snow, leaves, or bird nests, which can create excessive backpressure. To check for blockages, inspect the vent pipe running to the exterior of your home.
Identifying and Clearing Blockages in Furnace Pressure Switch Vents
Next, remove the tubing from the switch and blow through it; if air does not flow freely, the system is obstructed. Blockages in the flue vent, a failing inducer motor, or a clogged air filter can prevent the switch from sensing the proper airflow.
More About How to check a furnace pressure switch
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