How to check the compressor of a split system air conditioner: diagnostic nuances + tips in case of breakdown

A significant component of a split system, of course, is the refrigeration compressor.It is thanks to this component of the technological scheme of a household or other machine that the cooling effect, as well as the effect of air humidification, is achieved.

If it happens that the compressor unit does not work for some reason, the split system essentially turns into an ordinary windmill. The desired effect from such a “mill” can no longer be obtained, and it’s time for the owner of the system to think about repairs.

However, in order to repair, you need to know how to check the split system air conditioner compressor for malfunction. This is exactly the question we will deal with in our article. We will also consider the module design, common types of faults and provide repair recommendations.

Compressor module design

To begin with, briefly about the refrigeration compressor, as a module that forms part of the air conditioner. This equipment belongs to electromechanical devices, the distinctive feature of which is the complete sealing of the internal contents.

That is, in case of any mechanical (electrical) malfunctions, you cannot simply take and disassemble such a device, like many others, in order to get to the faulty unit. Everything is much more complicated here. In some cases you will even have to perform dismantling the split system.

That is why, in case of serious malfunctions, it is easier to replace a split system refrigeration compressor with a new one rather than try to repair it.

Examples of compressor units from the variety of options that are used on household split systems. The classic shape is usually cylindrical, but in terms of overall dimensions there is a wide variety of designs

Generally speaking, the mechanical design of a refrigeration compressor resembles that of a traditional air compressor.

The machine also contains a connecting rod and piston system, although often of a rotary type, bearing units, and a valve system. But all this is contained in a hermetically sealed metal case.

External and internal structure of the compressor: 1 – bearing balancing unit; 2 – channels for oil; 3 – drive motor; 4 – spiral design; 5 - discharge pipe; 6 – valve system; 7 – coupling; 8 – oil pan; 9 – support base

There, inside the housing, the electric drive is mounted. The drive system is made in such a way that the winding of wires, which does not have air cooling, receives cooling from the working refrigerant - freon

This fairly effective method of internal cooling ensures the longevity of compressor motors. In practice, malfunctions of electric motors are observed, but quite rarely.

Signs of a compressor malfunction

It should be clear that when the split system is not able to provide the specified temperature, this factor may indicate that the compressor is not working.

In addition, the operation of the air conditioning compressor unit is clearly determined by the characteristic noise effect created by the refrigeration unit.The noise of the equipment cannot be said to be strong, but when the unit is operating, it can be heard reliably.

If a decision is made to repair internal defects in a refrigeration compressor, it is necessary to dismantle the device from the system, having first freed the circuit from the refrigerant

By the way, again, based on the noise level, some types of defects in the compressor machine are determined. So, if an increased clicking or grinding sound is noted during operation, most likely, wear or damage to the valves can be detected.

With such a malfunction, the performance of the compressor drops sharply, and the body of the device becomes very hot. Ultimately, the internal thermal relay, machine operation is blocked.

Often there is a situation where almost immediately after starting the compressor, its operation stops. However, the device itself is actually intact and functional.

The cause of the defect in this situation is usually a lack or overfilling of the refrigerant circuit. An emergency stop is provided by a thermal relay, which, by the way, can also fail.

One of the thermal relay designs, one of those used to protect the split system compressor from heating above the permissible temperature. Meanwhile, this device may also be faulty

Finally, the owner of a split system may be faced with a working moment - when the compressor unit simply does not start. At the same time, the air conditioner is quite functional in terms of all other functions.

The compressor does not give rise to any evidence of defects—outwardly it looks intact and unharmed. The traditional reason for this option, as a rule, is the inoperability of the starting capacitor with a capacity of 10 μF or more.

This is what the capacitors that are responsible for starting the split system compressor look like. Depending on the power of the compressor unit, the working capacity of such parts varies

The most severe and practically irreparable defect of a split system compressor is an interturn short circuit in the stator windings of the drive motor. True, we should pay tribute - in modern designs of hermetic compressors such a malfunction rarely occurs.

Checking the device depending on the defect

Let's consider the possible actions of a mechanic or split system user, taking into account all the faults noted above.

But first you should take note of the following points:

1. Such equipment is serviced by specialists. We talked about cleaning the split system yourself Here.
2. The system is filled with chemically harmful substances.
3. The device operates from a high-potential network.
4. Electrical, electronic and mechanical knowledge is required.
5. There is a danger of harm to health.

A calm, reliable and qualified way to check the system is, of course, to turn to professional technicians.

However, the possibility of using personal skills and abilities at your own peril and risk is not excluded. For the second option, we will consider ways to check equipment for malfunctions.

Problem #1 - high level of mechanical noise

So, if a machine makes increased noise that is not typical for normal operation, we can state with high confidence that the internal components are destroyed.

These can be bearing units, valve group parts and others. In such cases, the only possible option is to replace the unit.

An attempt to repair a unit that has received internal damage. To access the internal contents, I had to cut the body with a cutting wheel. Meanwhile, after the repair you will have to seal the case hermetically   

Increased noise can also be observed due to excess refrigerant charged into the system. However, in this case, the nature of the noise is clearly different from mechanical noise, and after a short period of operation, the compressor is usually turned off by the automatic system according to the high pressure parameter.

Checking for these two options is accompanied by the following actions:

1. Connect the pressure gauge station to the pressure side.
2. Close the system tap on the circuit line.
3. Monitor pressure readings.

With faulty valves, the noise level usually increases, but the pressure does not actually change or changes only slightly. If the bearings are faulty, an increase in noise will be accompanied by an increase in pressure.

Using a pressure gauge station to check the amount of refrigerant in the circuit pumped by the compressor. Often, due to a lack or excess of working substance, the operation of the unit is disrupted

An excessive amount of refrigerant in the circuit will also show an increase in pressure with an increase in noise and subsequent shutdown of the compressor by the automation system (pressure switch). We wrote more about the design of this unit, its operating principle, connection and adjustment in next publication.

Problem #2 - overflow or lack of freon

A “fault” of this kind is determined, again using a pressure gauge station. It is necessary to disconnect the split system from the network, wait a little, then connect the pressure gauge station and start the air conditioner. Observe the readings on the instruments.

The operating pressure for a household split system of a specific configuration can always be determined by the technical tag (plate) attached to the body of the external module. There, on the plate, the boundary pressure parameters of the discharge and suction contour sections are indicated.

A plate with limit parameters indicating the limit values ​​of discharge and suction pressures. In case of troubleshooting, it is recommended to refer to this plate

If the table limits are exceeded, this indicates that the system is clearly overfilled with refrigerant. However, the table gives only upper pressure values.

Therefore, the lack of refrigerant is determined somewhat differently. The average suction pressure for household split systems is approximately 4-6 Bar (ATI), depending on the configuration.

When the pressure indicator of the suction part of the circuit at the pressure gauge station is significantly less than the specified range of 4-6 Bar, this factor indicates a lack of filling.

This condition also affects the operation of the compressor, with abnormal noise and intermittent activation of protective systems.

Problem #3 - refrigeration compressor does not start

A common compressor-related defect in split systems is the complete lack of starting time for the refrigeration compressor. In this case, the system successfully switches to cooling mode, all automation devices work normally. Another issue is the condenser fan.

The split system fan stops immediately when the air conditioner is turned on - this is a clear sign of failure of the starting capacitor, through which the compressor unit is supplied with current.

In this condition of the split system, the condenser fan shows somewhat unusual operation. When the air conditioner starts, the fan impeller begins to rotate, but almost immediately the rotation stops.

The indoor unit of the air conditioner continues to function when the compressor of the outdoor unit is not working.

This defect, as a rule, appears on systems that have successfully operated for several years (more than 5). And the reason for this behavior of the system is the starting capacitor connected to the power supply circuit of the compressor motor.

Diagnosing a faulty capacitor is easy. How to do this is below.

Problem #4 - turn-to-turn short circuit of the stator winding

How to determine such a malfunction is a far from ambiguous question. For example, when there is a short circuit of 2-3 turns in a short section, it is almost impossible to determine the defect without the use of a specific tool.

Damaged winding of the split system compressor. In this case, there is a break in individual conductors. This type of repair is only possible in a workshop, and even then not always with positive success.

Other variations, when sufficiently distant sections are closed to each other, can, in principle, be determined by simply measuring the resistance of the working windings of the motor stator.

Typically, the winding where there is a “short” winding gives less resistance relative to other windings. However, an accurate motor diagram will be required.

Tips for repairing equipment

Internal defects of the split system compressor are corrected exclusively in professional workshops.At home, repairs of such complexity by the owner himself seem irrational, with an extremely low percentage of successful completion.

If the normal operation of the compressor is disrupted due to excess or lack of refrigerant, it is quite possible to solve the repair problem yourself.

In the first case (excess freon), it is enough to simply remove some of the gas from the system. In the second case, you need the opposite - recharge the system additional gas volume.

With an interturn short circuit, repairs at home seem to be a futile exercise. Such a malfunction is difficult to eliminate even in a professional workshop.

When the cause of the compressor inoperability is the starting capacitor, you should open the top cover of the external system unit, having first disconnected the machine from the power supply.

Remove the capacitor and check with a tester in resistance measurement mode (mOhm), alternately touching the working terminals with the probes. A non-working capacitor will not show the discharge effect. This is the reason for replacement.

Conclusions and useful video on the topic

This video was filmed by specialists and may be useful to those who are eager to repair a split system compressor that has serious damage.

The operation of modern split systems shows quite long-term operation without the need for repairs. Moreover, if we are talking about serious defects, such as interturn short circuits or mechanical wear.

Simple faults can be repaired quite simply, and in the case of complex defects, replacing the split system with a new one seems like a reasonable solution. Serious repairs will force you to spend the same amount of money as required purchasing a new split system.

Would you like to share compressor diagnostic methods that we did not talk about in this material? Write your comments, additions and recommendations in the block below.

If you are trying to independently figure out the reason for the breakdown of your split system and find yourself in a difficult situation, do not hesitate to ask for advice from our experts and other site visitors in the comments to this article.