The compressor fails to start and makes a "buzzing" sound. The fault may be here

Fault description: Hisense kfr-25gw hanging air conditioner does not cool after startup.

1. Measure the compressor voltage and coil resistance

Door to door inspection: the user normally uses the air conditioner, feels natural wind at the air outlet of the indoor unit by hand, and goes to the outdoor unit for inspection,

It is found that the outdoor fan operates but the compressor does not operate, as shown in the left figure of Figure 2. Use the AC voltage block of multimeter to measure the terminal voltages of 2n (power zero line) and 3cm (compressor power supply) on the wiring terminal of outdoor unit. The normal voltage is AC 220V. The measured voltage indicates that the main board of indoor unit has been supplied with power.

Disconnect the power supply of the air conditioner, use the resistance gear of the multimeter to measure the 2n and 3cm terminal resistance (equivalent to measuring the common end and operating winding of the compressor). The normal value is about 30, and the measured result is infinite, indicating that there is an open circuit fault in the compressor coil circuit.

2. Cool the compressor

Ask the user that the air conditioner has been on for a period of time, touch the outdoor unit shell corresponding to the compressor with your hand, and roughly judge that the contact of the overload protector inside the compressor is disconnected.

Remove the outdoor unit shell, touch the compressor shell to make sure that the contact of the internal overload protector is disconnected due to high temperature, put a towel on the upper part of the compressor, cool it with cold water, and measure the resistance of 2n and 3cm terminals. When the resistance is changed from infinity to normal, it means that the contact of the internal overload protector is closed.

Note: the overload protector inside the compressor is connected in series at the common end of the compressor coil and is located at the upper top shell. When cooling the compressor with cold water, put a towel on the top to quickly close the contact of the overload protector.

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3. The compressor cannot be started

After the resistance values of 2n and 3cm terminals are measured to be normal, power on and start the machine, as shown in the left figure of Figure 4. The compressor makes a "buzzing" sound for about 30s and stops for about 20s to make a "buzzing" sound again.

When the compressor is started, use the AC voltage gear of the multimeter to measure the voltage of 2n and 3cm terminals,

When the AC voltage drops from 218v (voltage without sound, i.e. static) to 199v (voltage with "buzzing" sound from the compressor, i.e. dynamic), it indicates that the power supply is normal.

Use the AC current gear of the multimeter to measure that the current of the compressor is close to 20a, and comprehensively judge that the compressor cannot be started.

4. Check compressor capacitance

On the premise of normal power supply voltage, the most common reason why the compressor cannot start is that the starting capacitor has no capacity damage. Remove the capacitor and measure it with the capacitance gear of the multimeter. There is only a few micro methods in the actual measurement, so it can be determined that the capacitor has no capacity damage.

5. Maintenance measures

Replace the compressor capacitor. After replacement, power on and start the compressor, the compressor runs, the air conditioner starts cooling, and the current of the compressor is measured to be 4.4a again. The fault is eliminated.

6. Summary

① Compressor Capacitor damage accounts for a large proportion of non refrigeration faults, which usually occurs after 2 ~ 3 years of service.

② If the user reports that it is a non refrigeration fault, the user shall be informed not to turn on the air conditioner, because if the fault is caused by damage to the compressor capacitor or lack of fluorine in the system, the compressor temperature will be too high, resulting in the disconnection of the built-in overload protector. During maintenance, the compressor shall be cooled to increase the maintenance time.

③ In the actual maintenance, if the fault is that the compressor cannot start and makes a "buzzing" sound, the fault can be eliminated without measuring and directly replacing the compressor capacitor; The newly replaced capacitor can be used normally if the error of capacitance is within 20% of the original capacitance.