With the development of motor technology, compressor is considered as "general machinery", especially in coal chemical industry, machinery industry and other industries.

For distance measurement applications, both incremental and absolute encoders can be chosen - from a technical point of view. The advantages of absolute encoders are reflected in accuracy and performance, while incremental encoders seem more economical and practical.

A correctly working compressor determines the safe operation of the whole air conditioner or refrigerator. For example, during the operation of piston compressor, there would be burnout, oiler failure or low pressure and gas shortage. Once these problems occur, the appliance would not work right.

How to quickly and accurately detect and solve these problems in time affects the compressor operating rate and product output.

This article will analyze all common faults of AC compressors and provide solutions.

Tecumseh Compressor AE4430YS

Figure 1: A refrigeration compressor manufactured by Tecumseh.

From the perspective of airflow, a possible fault is that the wind pressure or the temperature of compressed air is too high, which may cause spontaneous combustion of carbon deposits and explosion of the pressure vessel if the protective device fails.
Another possible problem is that the air volume is insufficient or the air volume is too low, which will affect production.

Common failures of compressors

Figure 2: Common failures of compressors

From the perspective of the compressor structure, there are four types of problems: problems of lubrication system, cooling water circuit, compressed air circuit and mechanical failure.

1. Compressor Shell Burnout

When a piston compressor is in operation, the Babbitt layer of the main bearing shell or connecting rod bearing shell may be burnt or fall off. This causes the temperature of the bearing shell to rise, producing high temperature and smoke, making the Babbitt alloy melt.

the main bearing shell or connecting rod bearing shell of air compressors can get burnt

Figure 3: Burnt shell of an air compressor with black ashes and carbon left inside it.

1.1 Low Oil Temperature

In the past, we are worried about the high oil temperature of the crankcase that can cause burnout. It is stated in the manual that the oil temperature cannot exceed 60℃ or 70℃, but there is no lowest limit.

However, oil temperature lower than the standard may cause the same fault. In winter, after the compressor is shut down, the oil temperature in the crankcase of compressor is lowered. So the oil is very viscous and shell is burned after the machine is turned on again. Therefore, it is better to use low-consistency oil in winter.

1.2 Low Oil Level in Crankcase

If the lower hole of the oil level is blocked, the dropping oil level cannot be found. And if the crankcase oil level is too low, the oil pump will suck in air intermittently.

Air drag is generated in the drain pipe, causing the oil film of the bearing shell damaged. Afterwards, the compressor shell will be poorly moisturized gradually, and it leads to burnout in the end.

1.3 Clearance Between Bearing Shell and Shaft

We used to adopt the method of pressing lead wire to measure the clearance between the bearing shell and the shaft.

This method is suitable for measuring the main bearing shell because the main bearing is fixed and the upper shell cover is buckled on the main journal that will not move when the bolt is tightened.

However, the method is not appropriate for measurement of connecting rod bearing shell. When tightening the connecting rod, the lead wire will be squeezed. If the connecting rod is tilted, it cannot truly reflect the clearance.

Therefore, we should use a dial indicator to measure the clearance according to the size of shaft.

the lead wire is squeezed in the clearance between bearing shell and shaft in an air compressor

Figure 4: Bearing shell between crankshaft and crankcase in an air compressor

2. Oil Injector Failure

2.1 Fail to Fill Oil

If the oil injector is not filled with oil, it should be disassembled and inspected.

If the plunger and the pump body are excessively worn, causing the gap to increase and the pressure oil to leak back, you should clean, and repair, and replace them.

2.2 Fail to Suck Oil

If the oil injector does not suck oil, and it does not drip oil when viewed from the oil cover, it means that the oil suction valve is stuck, or the oil cover is not installed tightly, and the air has entered.

It is necessary to clean the oil suction ball valve in the oil injection pump and replace the rubber ring of the oil cover.

2.3 Insufficient Oil Supply

Insufficient oil supply of the oil injector is due to long-term operation with uncleaned system, which has resulted in pipeline blockage finally. Or it may be that the nut joint is not tightened after overhaul, causing oil leakage. To solve it, you should clean the pipeline and tighten the joints.

Simatec 60mL automatic oil injector

Figure 5: Automatic oil injector

3. Low Pressure and Insufficient Air Volume

When the compressor pressure is low and the air volume is insufficient, if there is no air leakage in the compressed air pipeline, it is usually the problem of the compressor unit itself.

There are several problems that cause the insufficient exhaust volume of the compressor unit.

3.1 Timely Maintenance

First of all, check whether the compressor discharge has decreased after maintenance. How long has the service lasted? If the environment is not ideal, check whether the air filter is blocked when the compressor runs for 2000 hours.

If the the air filter is not blocked seriously, you can just carry out a dust removal procedure. If the blockage is serious, you should replace the old air filter with a new one.

Most of the time, there is no big problem when the discharge of the compressor drops. The problem is that the customer neglects the maintenance and the air filter of the compressor is blocked. After replacing a new air filter, the compressor can work normally.

Video 1: How to maintain an air compressor. (Credit: Master Tool Repair on YouTube)

In addition to air filter, lubricant and other filter elements are also critical. Check whether the lubricant is within the standard range. If it is missing, please add it appropriately.

3.2 Open Intake Valve

If the discharge of the compressor decreases, check the unit.

If your compressor has just been served with a maintenance service, and there’s no problem in three filters and oil products, a technician should check the intake valve of the compressor.
Remove the intake hose, open the compressor, and watch whether the opening of the intake valve is normal.

inner view of an intake valve of air compressor

Figure 6: Intake valve of an air compressor

Generally, the theoretical design service life of the intake valve is 100000 times. Due to the different brands and batches of each manufacturer, the quality may be different. Therefore the failure of the intake valve may lead to the decrease of the unit's exhaust volume.

If the intake valve cannot be fully opened when the compressor is loaded, it can be concluded that the decrease of exhaust volume is the fault of the intake valve, which should be removed for maintenance or replacement.

3.3 Motor Failure

After the troubleshooting of the intake valve, and the exhaust volume of the unit is still unchanged, you should consider whether the motor is functioning well.

Due to local short circuit in the motor coil, or bearing wear and motor shaft wear, the motor speed is lower than the rated speed, which reduces the discharge capacity of the compressor. The motor coil and bearing should be overhauled, and the discharge capacity of the compressor should be tested after repair.

3.4 Working Pressure is Set to Be Low

If the working pressure switch of the compressor is set to be lower than standard, it should be raised to an upper value.

During factory debugging of the compressor, the working pressure is set according to customer needs. During customers’ use period, it may be set at a differential pressure. For example, when the compressor starts to pump air into the air tank, and the pressure reaches 10kg, the compressor stops or unloads. When the pressure reaches 7kg, the compressor starts up again. There is a pressure difference between them. This process can leave the compressor with a rest to protect it.

Sunny pressure switch with unloading valve and heavy duty 25 Amps at 230 volts

Figure 7: Sunny pressure switch with unloading valve

Different compressor switches have different adjustment methods. One is that the pressure difference is fixed by the switch itself, which only regulates the automatic shutdown pressure and the maximum pressure. This kind of switch is equipped with two buttons adjusted by a slotted screwdriver. The two buttons must be adjusted in the same way. Otherwise, they will move together and stop, stop and start again, and burn out the electrical appliances.

The other is to regulate the starting pressure (low pressure) and the stopping pressure (high pressure).

* Compressor Pressure Adjustment

Turn the pressure adjusting screw clockwise to increase the closing and opening pressure simultaneously. Turn the pressure adjusting screw anticlockwise to decrease the closing and opening pressure simultaneously.

* Compressor Differential Pressure Adjustment

When the differential pressure adjusting screw is rotated clockwise, the closing pressure does not change and the opening pressure increases. When the differential pressure adjusting screw is rotated anticlockwise, the closing pressure remains unchanged and the opening pressure decreases.

If it’s the pressure switch failure that causes a working pressure error, you should replace the pressure switch if it cannot be repaired.

3.5 Change of Environment

workers and equipment work in high altitude place may need additional adjustment

Figure 8: Workers rest in mountainous workplace of high altitude

If a compressor was used in a low altitude area at first, and was moved to a high altitude area with other equipment due to the relocation of the factory, and the environment became humid, which may lead to the decrease of the unit discharge.

The higher the altitude, the thinner the air and the smaller the gas production per unit time. If there’s too much water in the air, the compressed air will contain a lot of water naturally. In the processing afterwards, the participation of water vapor will result in reduced exhaust.

3.6 Loose Belt of Compressor Drive

In this case you should adjust the drive belt. If it’s damaged, replace it with a new one.

According to the matching of the pulley and the shaft, the proper positioning method should be selected.
The pulley is installed on the compressor head shaft and compressor motor. Firstly, the pulley of the compressor head is fixed and locked.

If it’s loose, you can tighten it with a soft copper, aluminum or rubber hammers.
If it’s tight, the pressing or heating red pressing method can be used for assembly, and the heating temperature should be controlled at 120-150 ℃.

If the tolerance fit of the taper sleeve pulley is slightly tight, the inner hole of the cone sleeve can be slightly extended and installed on the shaft.

The verticality of two belt wheels and the same reference plane shall be measured with a horizontal ruler (accuracy ≤ 0.5mm), and the allowable error shall be ≤ 0.5mm.
The verticality error is greater than 0.5mm. The installation foundation of compressor head or compressor oil gas drum can be adjusted by using gasket, to ensure that the vertical error of the same datum plane is not more than 0.5mm.

You should also tighten the compressor head or compressor oil and gas drum mounting bolts. Install the belt on the pulley according to the principle that the trademark is in the same position. Take small pulley as the benchmark, measure the plane straightness of two belt wheels with a ruler or laser measuring instrument, and the allowable error is ≤ 0.5mm.

loose or tight or worn belt affects the operation of air compressor as well

Figure 9: Inspect and adjust belt of air compressors

Tension the belt with the compressor motor adjustment screw. On the contrary, take the large pulley as the benchmark, recheck the flatness straightness of the two pulleys, and the allowable error is less than 0.5mm. Finally, lock the adjusting screw and nut.

The belt replacement is the same as the belt adjustment. Only attention should be paid to the replacement of the belt, and not only one belt, otherwise, the new belt will be damaged due to the different belt tension.

Do not splash lubricating oil on the belt or pulley in case of belt slipping. Check the belt after the first operation of the new machine for 30h. If there is any slack of compressor belt, it should be adjusted immediately.

4. Problems and Solutions by Compressor Types

There are several kinds of compressors according to their different principles and structures, including piston compressor, rotary compressor, centrifugal compressor and axial flow compressor. Plus the application occasions and usage methods of each type of compressor are different, different failures will occur.

If you want to know the detailed introduction about compressor types, check this article:
Common Types of Refrigeration Compressors: A Comprehensive Guide

Afterwards we will analyze the special problems of some common compressors and propose solutions, such as piston compressors, centrifugal compressor, and screw compressors.

4.1 Piston Compressor Troubleshooting

Common problems of piston compressors can be summarized as follows:

* The compressor cannot start normally
* The compressor starts and stops frequently
* Liquid hammer phenomenon of compressor
* Excessive noise in operation
* Abnormal discharge pressure and discharge temperature
* Abnormal compressor oil pressure

Danfoss Compressor MLM019T5LP9

Figure 10: Piston compressor made by Danfoss, MLM019T5LP9.

Please check our another article for detailed faults and solutions for piston compressor:
List of Problems and Solutions for Piston Compressors

4.2 Centrifugal Compressor Troubleshooting

Common faults of centrifugal compressors can be summarized as the following 11 points.

* Abnormal vibration and noise
* Bearing failure
* Thrust bearing failure
* The oil seal ring and the seal ring are faulty and the seal is unstable
* The sealing system is unstable and abnormal
* Performance does not meet the requirements
* Surge
* The impeller is damaged
* Leak
* Insufficient flow and exhaust
* Prime mover overload

You can read our detailed article about these faults and solutions for centrifugal compressor:
List of Problems and Solutions for Centrifugal Air Compressor

4.3 Screw Compressor Troubleshooting

Screw compressors as one type of compressors that are commonly used, with 11 common faults.

* The compressor cannot be started
* The compressor cannot build pressure
* Too high Exhaust temperature or over temperature protection
* Frequent conversion between full load and no-load operation
* Fail to work without load; cannot maintain pressure or safety valve action when no-load
* Exhaust volume or pressure is lower than normal
* Large oil content in exhaust gas, high oil consumption of compressor
* Oil spill
* Abnormal sound of the unit
* Overload protection
* During the start-up process, the host is overloaded or blocked. The main contactor often acts

Here’s the article about the faults and solutions for screw compressors in detail:
List of Problems and Solutions for Screw Compressors

In general, there are a variety of compressors, and they may have different problems due to different work environments and operating methods. At this point, different solutions are needed. However, the structural principle is almost the same, as well as similar basic operation method. Therefore, in reality, similar problems of different compressors can be used for reference.