If it is ensured that the air conditioner failure is caused by the damage of the motor start capacitors. The damaged compressor start capacitor needs to be replaced.
Replacing the start capacitor can generally be divided into three steps. Removing the start capacitor, finding a replaceable start capacitor, and replacing the start capacitor.
How to Replace Motor Start Capacitors?
Remove the start capacitor
The compressor motor start capacitors are located on the circuit support board above the compressor. When disassembling, unplug the connecting wire and use a screwdriver to remove the fixing screw of the snap ring.
Looking for replaceable capacitors
After removing the damaged compressor start capacitor. Select a suitable new start capacitor to replace it according to the specifications and volume of the damaged start capacitor.
The specific content of how to select the start capacitor will be explained in detail below.
Replace the start capacitor
After selecting the compressor motor start capacitors, install the new compressor start capacitor in the outdoor unit, fix the metal fixing ring, reconnect the connecting cable, and then power on and test the machine to complete the replacement.
How Test the Motor Start Capacitors of a Fan?
- Connect all parts on the circuit board of the air conditioner completely.
- Turn on the power supply.
- Use the remote control to adjust the temperature to make the fan motor rotate.
- Connect the ground terminal of the oscilloscope probe to the ground terminal of the circuit board.
- Use an oscilloscope probe to detect the white lead on the Hall element plug.
- The oscilloscope shows signal waveform.
When testing the start capacitor of the fan motor, a multimeter should be used to measure the resistance of the capacitor. Due to the large size of the capacitor, it is impossible to use the capacitor input jack for testing. At this time, you can use the multimeter pen to test and judge the quality of the capacitor by the change of the value displayed by the multimeter.
If the resistance value displayed by the multimeter changes from small to large and then changes to infinity, it means that this is a good capacitor with charging and discharging functions. Check again after changing the test leads, the displayed value still changes from small to large, and changes to infinity.
After measuring the capacitor, if the test leads are not replaced when the test is performed again, and the resistance value is displayed as infinite, it means that charging and discharging are not performed, but it does not mean that the capacitor is damaged. Therefore, when testing the capacitance, the test leads must be replaced no matter which multimeter is used?
How to calculate the voltage across the run capacitor of a single-phase motor?
First of all, you must know the impedance value of the secondary winding. You can measure the resistance value by measuring the DC resistance with a multimeter. Then, the secondary winding is connected to a 12V AC voltage and the current value is measured. According to the winding impedance equal to the resistance and reactance in series, it can be calculated by phasing out the winding inductance value.
In normal operation, the capacitor is connected in series on the secondary winding, that is, the three equivalent parameters of winding resistance, winding reactance, and capacitance are connected in series and then connected to 220V voltage. It is easy to calculate the phasor according to the formula of the series circuit. Calculate the voltage on the capacitor.
When a single-phase motor is running, the voltage at both ends of the capacitor is generally above 300VAC, so the capacitor voltage is generally selected for a capacitor with a withstand voltage of 400V or more, and a capacitor with a voltage of more than 450V is better. First, measure the resistance R and reactance XL of the secondary winding, and then select the capacitance C according to the power of the motor to calculate the capacitive reactance Xc.
C: Capacitor capacity: I: motor rated current, U: motor rated voltage, cosφ: power factor 0.7.
Calculating Capacitors Capacity
Generally, there is no need to calculate. The run capacitor is 2~3μF per 100W, and the start capacitor is 2~3 times the run capacitor. The capacitor selection of the motor has strict requirements on the voltage, and it must be equal to or greater than 1.5 times the rated voltage of the motor. For a power supply with a rated voltage of 220V, the rated voltage of the capacitor cannot be lower than 400V. The capacitance value has a certain broadness. It doesn’t matter if it is larger or smaller, especially the start capacitor, which can be selected at 2-6 times the working capacitor.
Precautions when replacing the starting capacitor
Starting capacitors are an important part of electronic circuits. If the starting capacitor is damaged, the motor cannot be started. Damaged starting capacitors must be replaced immediately. They will emit buzzing and current surge noises only when energized for a short period of time, and overheating and engine fatigue will occur if they are energized for long periods of time. And it is not difficult to determine that the starting capacitor is broken. Most damaged starting capacitors swell and excessive current burns the surface, slowing down and weakening the rotor. Of course, the most intuitive and accurate way is to use the amplitude setting of the multimeter to measure quality.
Things To Keep In Mind Before Replacing The Capacitor
Once you’ve checked for a defect in the start capacitor, here are a few things to keep in mind when replacing the start capacitor:
Even after the start capacitor has been discharged, some residual charge remains. This charge cannot be discharged for a while, so it is necessary to carry out artificial discharge again.
A failed starting capacitor may not partially discharge due to defective lead contacts, internal disconnection, blown fuses, etc. Therefore, maintenance personnel should wear insulating gloves before touching a failed starting capacitor. You can use a short circuit wire to short the two poles of the failed capacitor first and then remove and replace it manually.
If multiple starting capacitors are used in series, they must be discharged separately.
When dealing with or replacing a failed start capacitor, turn off the starting capacitor and disconnect or disconnect it to discharge the starting capacitor.
When discharging, first connect the ground terminal of the ground wire, and then use the ground rod to discharge the start capacitor several times until the discharge sparks and discharge noise are gone, and then repair the ground terminal.
In addition, the instruction manual is often ignored by the general public. So please understand the precautions for use before use. As you know, the resistance of a capacitor is inversely proportional to its frequency. The lower the frequency, the lesser the loss. Measures must be taken to limit the harmonics and currents flowing in the circuit. Pay special attention to ventilation and cooling, as condensate will always generate heat.
After installing the static VAR compensator, the system should be tested during operation and action should be taken in time if excessive voltages, excessive currents, oscillations or harmonics are found. This is very necessary in the normal case. intensive process.
How to test a motor starting capacitor without a multimeter
A DC voltmeter can be connected in parallel with the capacitors and a dielectric shaker. It can be used to charge the capacitor (note the + and the poles).
Check if the voltage can rise to the rated voltage of the capacitor.
0V, the capacitor is short-circuited.
It slowly rises to the rated voltage of the capacitor, which proves that the capacitor is good.
If the voltage rises rapidly to the rated voltage of the capacitor and the insulation resistance is approximately the same as the internal resistance of the DC meter, the capacitor is open.
After settling at the rated voltage of the capacitor, check the insulation resistance of the capacitor.
Since the insulation resistance is close to the internal resistance of the DC meter, the capacitance is good.
If the insulation resistance is smaller than the internal resistance of the DC meter, the capacitor leaks too much and heat is easily generated, making it unusable.
