A21
IVT
Circulation fan speed control fault
Furnace shows fan speed error; circulation blower not reaching commanded speed
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed ECM blower motor, Faulty fan speed control module, Obstructed blower wheel, Wiring fault between motor and IVT control
How to Fix / Troubleshooting
Safety: Turn off power before accessing the blower compartment.
- Inspect blower wheel: Remove the blower access panel and check for debris, insulation, or objects lodged in the wheel. Clean as needed.
- Check motor harness: Ensure the multi-pin connector on the ECM motor or speed control module is fully seated and free of corrosion.
- Spin test: Rotate the blower wheel by hand; it should move freely without grinding. Stiff movement indicates bad bearings and the motor assembly should be replaced.
- Observe startup: Restore power and call for fan operation. If the motor hums, starts slowly, or stops, the ECM module or motor windings may be defective.
ECM motor diagnostics often require manufacturer-specific tools; replacement is typically a professional job.
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Repair Difficulty
Hard
4/5
Required Part
IVT ECM circulation blower motor
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