First, disconnect the two wires connected to the switch terminals. Locate the unit's disconnect switch near the unit itself and ensure it is also turned off.
Understanding the Inducer Motor Pressure Switch and How to Test It
Also, examine the venting outside your home to ensure it is not clogged with snow, leaves, or bird nests, which can create excessive backpressure. Before you begin, you must turn off the power to the furnace at the circuit breaker.
Locate the switch, which is usually a small, rectangular device with electrical wires connected to the back and a rubber or plastic tubing connecting to the inducer motor housing. 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.
Understanding the Inducer Motor Pressure Switch Connection
With the furnace powered off and the inducer fan manually spun (if possible), you should hear a click or see a change in resistance. If the meter shows no continuity (infinite resistance), the switch is open and needs replacement.
More About How to check a furnace pressure switch
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