4 Ways to Test AC Compressor

Figure 1: Air conditioner outdoor unit.

The air conditioning compressor (AC compressor) is a key component in the air-conditioning system, and it is responsible for changing the refrigerant from a low-pressure state to a high-pressure state, thereby realizing the cooling effect of the air conditioner. Therefore, checking/testing the condition of the air conditioner compressor is the key to ensure the normal operation of the air conditioner.

The bad AC compressor symptoms include AC compressor not turning on, too large compressor operating current, abnormal noise, compressor leakage, etc. When you encounter the above problems, you can use the method described below to test whether the compressor is damaged.

1. How to Quickly Test the Air Conditioner Compressor

The test of the AC compressor is mainly carried out from the following aspects:
·First, test the motor winding in the compressor.
·Second, check the mechanical parts in the crankcase.
·Third, detect the technical parameters such as the working pressure and operating current of the refrigeration system.

The circuit control principles of AC compressors are common and generally include PSC start mode, CSR start mode and direct start mode (compressor powered by three-phase power supply) and IPM power module frequency conversion circuit drive mode of inverter AC compressor.

1.1 Test AC Compressor with a Multimeter

Ordinary Single-Phase AC Compressor Winding Test Method

Figure 2: Disassembled air conditioner outdoor unit.

When detecting the motor winding resistance value in the compressor,
1. First cut off the power supply;
2. Remove the panel of the air conditioner external unit, the compressor junction box cover and the connecting wires on the compressor terminals;
3. After zeroing the multimeter, use it to check whether there is a certain winding resistance value between the three terminals.

Identify what the three wires are based on the winding terminal identification on the compressor box cover or the symbols next to the compressor terminals. The connection terminals of general compressors are divided into，
·Common terminals, represented by "C";
·Run winding terminals, represented by "R";
·Start winding terminals, represented by "S".

Figure 3: The three terminals of the compressor.

Taking the detection method of a common single-phase compressor (powered by AC220V) as an example.

1.Connect the red probe of the multimeter to the "C" terminal and the black one to the "R" terminal, and the measured resistance value of the compressor winding (run winding) is about 3Ω.
2.Then connect the black probe to the "S" terminal, and the measured resistance value of the compressor winding (start winding) is about 7Ω. Generally, the resistance value of the common compressor start winding is greater than that of the run winding.

3.Connect the red probe to the "R" terminal and the black probe to the "S" terminal. The measured resistance value is 10Ω, which is the series resistance value of the run winding and the start winding, namely: Rsr=Rcs+Rcr (common winding resistance value of compressor=start winding resistance value+run winding resistance value).

Figure 4: Single-phase compressor circuit wiring diagram.

Generally, if the sum of the resistance values of SC and RC is equal to RS, the AC compressor is in good condition. If the deviation of the detected winding resistance value is too large or there is no resistance value, it is mostly because the compressor motor winding is damaged.

But sometimes, if the AC compressor is short-circuited, the multimeter cannot measure it, because the value displayed by the multimeter may be normal.
In this case, the easiest way is to measure the energization of the compressor with a multimeter. If it shows that it is powered on, but the compressor does not start, you can try to replace the starting capacitor. If the AC compressor does not start after replacing the capacitor, it is undoubtedly that the compressor is broken.

Inverter AC Compressor and Three-Phase AC Compressor Winding Test Methods

If the compressor motor is a three-phase motor, there are three symmetrical windings inside, which are U, V, and W (two terminals in one group). The three-phase electric power can generate the rotating magnetic field, and the motor can run without the starting circuit.

When detecting the resistance value of the motor winding in the inverter compressor or the three-phase compressor, the resistance values of the three windings of the compressor motor should be equal, otherwise, the winding is bad.

Figure 5: Three-phase inverter compressor circuit wiring diagram.

1.2 Inspect Mechanical Parts inside the AC Compressor Crankcase

(1) Check whether the power supply voltage of the AC compressor is normal. The normal voltage range should be the rated voltage ±10% . If the rated voltage is AC220V, the normal working voltage range is: 198V-242V, and the minimum starting voltage is above 187V. At the same time, ensure that the capacity of the power supply line and the material and wire diameter of the line meet the requirements.

(2) Check whether the components related to the compressor circuit are damaged, such as the running capacitor, starting capacitor and other components.

After confirming that the power supply voltage is normal and the components of the compressor-related circuits are not damaged, it can be determined that the mechanical parts of the compressor are failed, such as the phenomenon of cylinder sticking.

1.3 Check the Pressure of the Refrigeration System

When the working current of the AC compressor is too large or there is abnormal noise, in addition to checking the power supply, the pressure of the refrigeration system should be tested at the same time. The normal low pressure of R22 should be 0.4-0.6 MPa during cooling, and the high pressure should be 1.6-2.7 MPa during heating (the pressure of R410A and R32 is about 1.6 times that of R22). If the detected pressure is too high, it is mainly caused by excessive refrigerant filling or poor circulation of the refrigeration system.

1.4 Detect Insulation of the AC Compressor

For obvious compressor electric leakage, you can use a multimeter to measure the resistance between the terminal and the compressor shell. Normally, the resistance between the two parts of compressors should be ∞, but if the pointer of the multimeter remains at the initial position and does not move, the AC compressor is damaged due to electric leakage.

Figure 6: Install air conditioner.

2. Summary

When there is a problem with the AC unit compressor, before using the above four methods for detection, you can also start from the following aspects:

First of all, check the appearance of the air conditioner compressor to see if there is any oil leakage, water leakage, deformation, etc. If any abnormality is found, it should be dealt with in time so as not to affect the normal operation of the air conditioner.

Secondly, check the condition of the electrical circuit of the air conditioner compressor, check the power line, junction box, contactor, capacitor and other components to ensure that they are well connected and there is no burnout.

In addition, check whether the refrigerant flow of the air conditioner compressor is sufficient to ensure the cooling effect of the air conditioner.

Finally, check the noise of the air conditioner compressor to ensure that its noise level is within the normal range so as not to affect the normal use of the air conditioner.

In short, checking the condition of the AC unit compressor is the key to ensure the normal operation of the air conditioner and should be given attention to. First check the appearance of the air conditioner compressor, the electrical condition, the refrigerant flow, and finally the noise to ensure the normal operation of the air conditioner compressor.

If there is no obvious damage to the AC compressor, use a multimeter to detect the AC compressor windings to determine whether the compressor is damaged. You can use the AC unit compressor winding detection method described above.

If it is confirmed that the compressor is damaged and needs to be replaced, please contact a professional to help for AC compressor replacement. The AC compressor cost is expensive, but this is money that has to be spent in order for your air conditioner to cool properly.

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