How to Fix an AC Compressor?

Figure 1: GMCC AC compressor.

The compressor is the most important part of the refrigeration cycle of the air conditioner. The air conditioner compressor (AC compressor)is different from the non-moving parts such as the condenser and the evaporator, it needs to run at high speed during the system work, and it is also a high-precision device integrating mechatronics. So AC compressor faults often occur in actual use.

So how to repair the AC compressor after it fails? Before talking about the repair method, it is necessary to understand the method of compressor fault judgment to find out whether the compressor itself is faulty, or its related parts are faulty or other external factors are causing the fault.

1. Common AC Compressor Faults

The following are 7 common compressor faults:
●Compressor Motor Damaged
●Compressor Capacitor Problem
●Frequent Operation of Thermal Protection Device
●Thermal Protector Damaged
●Water Leaks into the System
●Abnormal Wear of the Compressor
●Compressor Stuck

1.1 Compressor Motor Damaged

1. The motor is burned due to the wiring of the compressor terminal being incorrect.

2. Refrigerant leakage. While the high-pressure gas is discharged from the compressor, it is also responsible for taking away the heat generated by the compressor motor.
If the refrigerant in the system leaks, only a small amount of high-pressure gas will be discharged from the compressor, so that the heat generated by the motor when it is working will always accumulate. If things go on like this, it will cause the compressor motor to burn out.

When the air conditioner compressor is stuck, the motor factor should be eliminated as much as possible first, so the insulation resistance of the motor and the windings of the main and auxiliary coils should be measured first to determine whether the motor is burned.

Figure 2: AC compressor motor.

1.2 Compressor Capacitor Problem

1. The capacitor is damaged (short circuit, open circuit);
2. The capacitor specification does not match the AC compressor.

This item applies to single-phase compressors only. Because of the use of a three-phase induction motor in a three-phase compressor, a rotating magnetic field is generated by feeding three-phase alternating current into the stator core, so a capacitor is not required.

1.3 The Thermal Protection of the Compressor Operates Frequently

1. The thermal protector is abnormal. Refer to the performance diagram and text description of this item in the specification provided by the AC compressor manufacturer.

2. The wiring of the power line is unreasonable (the wiring of the compressor terminal is not correct, or the frequency converter of the inverter air conditioner is running with a phase lost), and the compressor start at low voltage.

3. The air conditioner is started before the high and low pressure in the system is balanced. Generally, it is better to restart the air conditioner at least 3 minutes after it is turned off. It may also be that the capillary tube flow of the system is too small to balance the high and low pressure as soon as possible.

4. Liquid slugging caused by liquid return, starting after long-term shutdown, and starting at too low environment temperature.

1.4 Thermal Protector Damaged

The thermal protector is an accessory of the AC compressor, and its failure is generally caused by an open circuit or a lower operating temperature point.

An open circuit will cause the AC compressor not to work. The lower operating temperature point will cause the compressor to stop after working for a period of time and repeat this.

This problem is often confused with a slight short circuit of the winding. The difference is that the working current is normal when the thermal protector is damaged, and the current is relatively larger when the winding is short circuited.

Figure 3: Thermal protector for AC compressor.

1.5 Water Leaks into the System

The refrigeration cycle system has strict requirements on moisture, and it is generally stipulated that the moisture content in the system is less than 0.2ml. If water invades the AC compressor, it will cause serious damage to the compressor as follows:

1. Copper plating and rusting occur on compressor mechanical parts. Note: the high temperature will play a catalytic role. For every 10 degrees of temperature rise, the reaction speed will increase by about 2 times.
When the copper plating and rusting reach a certain level, the fit between the mechanical parts of the compressor will be reduced, and in severe cases, the compressor may be stuck.

2. The protective coating for motor coil and the insulating materials are corroded, resulting in a short circuit of the motor;
3. Deterioration of refrigerant and refrigeration oil;
4. The vane spring is brittle and broken.

In general, moisture intrusion may be caused by incomplete vacuumizing or the refrigerant leakage at the low-pressure side of the system.

Figure 4: Copper plating inside the compressor.

1.6 Abnormal Wear of the Compressor

1. It may be due to the small clearance between the internal parts of the compressor, which is generally a problem of the compressor itself;

2. Lack of refrigeration oil. Refrigeration oil plays a role of lubrication inside the compressor, and can effectively prevent the wear of the mechanical parts of the pump body.
Its oil seal function can maintain the pressure difference between high and low pressure areas, avoiding the gas in the high and low pressure areas entering each other and preventing the cooling capacity from decreasing.
In addition, the continuous circulation of the refrigeration oil can also take away the heat generated between the friction surfaces in time.

When the amount of refrigeration oil is insufficient, the mechanical parts inside the compressor will be abnormally worn out because they cannot be lubricated in time, which will eventually cause the compressor to be stuck.

Lack of refrigeration oil in the system may be caused by the following reasons.
A: Poor oil return hole;
B: The oil leaks together with the refrigerant;
C: Oil carbonization and deterioration;
D: Poor oil return in the system.

Figure 5: Air conditioner compressor is stuck.

1.7 Compressor Stuck

If the refrigeration oil is insufficient or there are impurities in the AC compressor, it will often cause the shaft to be locked or the cylinder to be stuck. The fault phenomenon is that the compressor does not run after being powered on, and the protector operates.

2. How to Fix Air Conditioner Compressor Faults

When there is a problem with components such as compressor capacitors and thermal protectors, the AC compressor can work normally after troubleshooting the relevant faults and replacing the corresponding components.

If there is a fault in the compressor itself, such as motor damage (winding short circuit, open circuit and winding grounding, etc.), wear and tear of compressor internal parts, the compressor needs to be replaced after inspection and confirmation.

If the compressor has a shaft-locking or cylinder-stuck fault, try to repair it first. The specific methods are as follows:
(1) Knocking method: After starting up, knock the lower half of the compressor with a wooden hammer to make the stuck parts inside the compressor vibrate and start running.

(2) Capacitor starting method: Use a capacitor with a larger capacitance than the original one to start.

(3) High-voltage starting method: Use a voltage regulator to increase the power supply voltage and then start the compressor.

(4) Pressure relief method: Start the compressor after all the refrigerant in the system is emptied.

If none of the above methods work, the only option is to replace the compressor.

Figure 6: Rotary compressor.

3. FAQs

3.1 Can the AC Compressor be Repaired If It is Broken?

Most air conditioner compressors cannot be repaired after they are damaged. Because the vast majority of air conditioner compressors are hermetic compressors, if the motor inside fails or the cylinder is stuck, the only way to repair it is to disassemble the compressor casing. But it cannot be restored after the casing is disassembled. So when the AC compressor is damaged, it can only be replaced with a new one.

3.2 Home AC Compressor Does Not Start How to Repair?

Troubleshooting methods for AC compressors not starting:

① When the compressor of the outdoor unit of the air conditioner does not start, it is mainly necessary to check whether there is any problem or damage with the compressor itself, the starting capacitor, or the starting relay.

② If it is normal after the above inspections, finally focus on checking the drive circuit components of the compressor.

3.3 How Much is an AC Compressor?

Around $200-$3,000. The air conditioner compressor is the core part of the air conditioner. Different brands and types of compressors vary greatly in price. Generally, the price of home AC compressors is around $200-$3,000.

3.4 How Much to Replace AC Compressor?

Around $400-$4,000. The cost of replacing an AC compressor is based on a single compressor, plus labor and installation costs, generally ranging from $400 to $4,000. In addition, depending on the type of air conditioner and the location of the installation, there may be some price fluctuations.

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