What happens
The fan cannot follow its command, or its speed feedback is missing or implausible.
Typical symptoms
Fan fault, intermittent rotation or no airflow with a valid demand.
Checks that distinguish this cause
Use the correct motor connector pinout and OEM command/feedback test. Isolate before inspecting or disconnecting connectors; distinguish motor supply, command and feedback from mechanical obstruction.
What can look similar
Indoor fan delay in heating or fan reduction near setpoint can be normal control behavior.
Repair direction
Replace the confirmed failed approved motor or board after checking the connected circuit.
Verify the repair
Verify stable commanded speed and valid feedback across supported fan modes.
Equipment-specific limits
Inverter electronics can retain dangerous DC voltage after supply isolation. Isolate all inputs, follow the specified discharge wait and prove the designated circuit safe with the OEM method. Never short a DC bus to discharge it, unplug powered motor connectors or insulation-test through connected electronics.
Practice this diagnosis
This cause is a reference topic; it does not yet have a dedicated simulated call. Browse the practice board.
References and applicability
Original HVACSim explanations with manufacturer and instrument-maker references for further reading. These resources support the subject; their model-specific examples are not specifications for every system.
- Haier: Arctic Next Gen service manualAW/1U EH2VHD model examples of inverter, motor, sensor and circuit diagnostics; obtain the installed model manual.
- Senville: R-454B model documentationSeparate installation and service documents for indoor styles and multi-zone generations.
Editorial review: 2026-09-29. Verify the current manual for the installed model.