Gas Furnace / Induced Draft
Pressure Switch Troubleshooting
Step-by-step diagnostic workflow for furnace inducer pressure switch faults, covers tubing, venting, condensate, inducer performance, wiring, and control board interpretation.
Safety Notice
Disconnect power before inspecting wiring. Combustion venting carries CO risk, ensure proper ventilation. Only trained HVAC technicians should diagnose live-voltage and combustion-related faults.
Confirm Call for Heat
Use a meter rated CAT III or higher when measuring line or control voltage.
Set the thermostat above room temperature to initiate a call for heat. Verify 24 VAC is present between R and W at the furnace control board. If no 24 V signal, the issue is upstream of the pressure switch, check thermostat wiring, transformer, and fuse first.
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