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How to determine whether the BLDC motor in the indoor unit of an air conditioner has malfunctioned?
Release Date:
2025-10-22
To determine whether the BLDC motor in the indoor unit of an air conditioner is faulty, you can perform a step-by-step troubleshooting process involving visual inspection, observation of operating status, and signal and electrical testing. The key is to distinguish between motor failure and control circuit failure.
To determine whether the BLDC motor in the indoor unit of an air conditioner is faulty, you can perform a step-by-step troubleshooting process consisting of visual inspection, observation of operating status, and signal and electrical testing. The key is to distinguish between motor failure and control circuit failure. The specific methods are as follows:
Step 1: Visual and Basic Inspection (with Power Off)
Cleanliness and Foreign Objects: After power is turned off, open the indoor unit’s front panel and inspect the motor surface for significant dust or lint accumulation, as well as any foreign objects that may be jamming the fan impeller. If the impeller is jammed, the motor may fail to start, or it may trip the overload protection and shut down shortly after startup.
Wiring and Connectors: Inspect the connection plugs between the motor and the air conditioner’s main control board for looseness, oxidation, or burn damage. Poor plug contact can cause unstable rotational speed, intermittent operation, and other issues; burned or blackened plugs with char marks are typically the result of excessive current or a short circuit.
Mechanical component condition: Gently flick the cross-flow fan with your hand. Under normal circumstances, the fan should rotate smoothly without any sticking or unusual noises. If there is significant rotational resistance or a “rustling” friction sound, it is highly likely that the bearing lubrication has failed or the bearing is worn; if the fan cannot rotate at all, the bearing may be seized, or iron filings may have become lodged between the rotor’s permanent magnets, causing jamming.
Step 2: Operational Status Observation (Power-On Test)
Startup failure:
After the air conditioner is turned on, the indoor unit fan does not rotate at all, and the unit displays a fault code (such as E1, E6, or E9 on most brands—refer to the user manual for specifics). If the remote control’s fan-speed setting and filter blockage have been ruled out, the fault can be attributed to a motor or drive-unit failure.
When the motor is started, it exhibits significant vibration and fails to operate normally, typically due to a faulty Hall sensor (which cannot detect the rotor position) or damage to the driver’s power devices.
Abnormal RPM and Noise:
When the remote control is used to adjust the fan speed, the motor speed remains unchanged (always at high or low speed). This could be due to a malfunction in the speed-control signal (the main board is not sending the command) or a failure in the motor driver’s reception.
During operation, high-frequency whining and a “buzzing” abnormal noise (not wind noise) occur, with the noise increasing as the rotational speed rises. After ruling out rotor blade dynamic imbalance, the most common causes are demagnetization of the rotor permanent magnets or localized short circuits in the stator windings.
Overheat protection shutdown: The motor suddenly stops running after a few minutes of operation, and part of the indoor unit’s casing becomes hot. After cooling down, it can briefly restart; this is most likely due to degraded winding insulation (causing excessive current from leakage) or poor heat dissipation from the driver.
Step 3: Signal and Electrical Testing (requires specialized tools)
Hall sensor signal detection: Use a multimeter or oscilloscope to check the Hall sensor’s power supply Vm (usually 5V) and output signal. If the power supply Vm is normal but there is no pulse signal output, it indicates that the Hall sensor is damaged.
Winding resistance testing: Use a multimeter to measure the resistance of the three-phase stator windings. Under normal conditions, the resistance values of the three phases should be uniform and consistent. If the resistance of one phase is infinite (open circuit) or significantly lower than that of the other two phases (short circuit), the winding is considered faulty.
Drive Input/Output Detection:
Test the speed-control signal output by the air-conditioner motherboard (a 0–10 V analog signal or a PWM pulse signal). If the signal is normal but the motor does not respond, it indicates a drive failure.
If the driver’s input Vm is normal (e.g., 310 V DC or 24 V DC, depending on the model), but there is no output current to drive the stator windings, it can be determined that the driver’s power module (IGBT/MOSFET) is damaged.
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