How to check the air conditioning compressor of a split system: nuances of diagnosis + tips for failure

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Victor Kitaev
Last update: May 2019

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

If it happens that the compressor unit for some reason does not work, the split system, in fact, turns into an ordinary windmill. The desired effect from such a "mill" can no longer be obtained, and the owner of the system just right to think about the repair.

However, in order to repair, you need to know how to check the air conditioning compressor of a split system for a malfunction. We will deal with this issue in our article. We also consider the device module, common types of malfunctions and provide recommendations for repair.

Compressor module device

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

That is, in case of any mechanical (electrical) malfunctions, you can not just take, disassemble such a device, like many others, to get to the faulty node. Everything is much more complicated here. In some cases, you’ll even have to complete dismantling a split system.

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

Compressors split systems
Examples of compressor units from those diverse options that are used on household split systems. The classical form, as a rule, is cylindrical, but in terms of overall dimensions the variety of designs is great

If we consider the machine in a generalized way, theoretically, the mechanical circuit of the refrigeration compressor resembles 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 enclosed in a hermetically sealed metal case.

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

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

This quite effective internal cooling method ensures the durability of compressor motors. In practice, motor failures are noted, but rarely enough.

Compressor Symptoms

It should be understandable 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 compressor unit of the air conditioner is clearly determined by the characteristic noise effect that the refrigeration unit creates. The noise of the equipment is not to say that it is strong, but during the operation of the unit it is audible with confidence.

Dismantling the air conditioning compressor
If a decision is made to repair the internal defects of the refrigeration compressor, you have to dismantle the device from the system, having previously released the circuit from the refrigerant

By the way, again, based on the noise level, some types of defects of the compressor machine are determined. So, if during operation an increased clicking sound or a rattle sound is noted, most likely, it is possible to state wear or damage to the valves.

With such a malfunction, the compressor performance drops sharply, the casing of the device is very hot. Eventually, the internal thermal relay, machine operation is blocked.

Often there is a situation when, almost immediately after the start of the compressor, it stops working. However, at the same time, the device itself is actually intact and operational.

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

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

Finally, the owner of the split system may encounter 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 a statement of defects - it looks outwardly 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.

Starting capacitors split systems
The capacitors responsible for the moment the compressor of the split system starts are approximately like this. Depending on the capacity of the compressor unit, the working capacity of such parts varies

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

Defect check

Consider the possible actions of a mechanic or user of a split system, taking into account all the malfunctions that were noted above.

But first, take into account the following points:

  1. Such equipment is maintained by specialists.We talked about self-cleaning a split system here.
  2. The system is charged with chemically harmful substances.
  3. The device operates on a high potential network.
  4. Requires knowledge of electricians, electronics, mechanics.
  5. There is a danger of harm to health.

A calm, reliable and qualified way to check the system is, of course, an appeal to professional masters.

Nevertheless, the possibility of using personal skills at their own risk is not excluded. For the second option, we consider methods for checking equipment for malfunction.

Problem # 1 - High Mechanical Noise

So, if the machine emits increased noise, not typical for normal operation, we can state with high confidence the destruction of internal components.

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

Air conditioning compressor repair
Attempt to repair unit that has received internal damage. To access the internal content, I had to cut the case with a cutting wheel. Meanwhile, after repair, you will have to tightly weld the case   

Increased noise may also occur due to excessive mass of refrigerant charged into the system. However, in this case, the nature of the noise is clearly different from the mechanical one, and after a short operation, the compressor is usually turned off by the automation system according to the high pressure parameter.

The check for these two options is accompanied by the following actions:

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

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

Pressure gauge connection
Using a gauge station to check the amount of refrigerant in the circuit pumped by the compressor. Often, due to a shortage or surplus of the working substance, the operation of the unit is disturbed

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

Problem # 2 - overflow or lack of freon

A “malfunction” of this kind is determined, again using a gauge station. It is necessary to disconnect the split system from the network, wait a bit, then connect the 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 housing of the external module. There, on the plate, the boundary pressure parameters of the contour sections of the discharge and suction are indicated.

Outdoor unit label
A plate with boundary parameters, where the boundary values ​​of the discharge and suction pressures are indicated. In case of fault diagnosis, it is recommended to refer to this label.

If the table limits are exceeded, this indicates a clear overflow of the system with refrigerant. However, the table only gives the upper pressure values.

Therefore, the lack of refrigerant is already determined in a slightly different way. The average norm of the 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 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 when abnormal noise and periodic operation of protective systems are noted.

Problem # 3 - no start of refrigeration compressor

A common defect in the split systems associated with the compressor is the complete absence of the start of the refrigeration compressor. At the same time, the system successfully enters the cooling mode, all automation devices work normally. Another question is the condenser fan.

Unit fan stopped
The split system fan is stopped 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, the split system of the condenser fan shows a somewhat unusual operation. When the air conditioner starts up, the fan wheel starts 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 idle.

This defect, as a rule, manifests itself on systems that have successfully worked for several years (more than 5). And the reason for this behavior of the system is the starting capacitor, included in the power circuit of the compressor motor.

Diagnosing a capacitor malfunction is simple. How to do this is a little lower.

Problem # 4 - inter-turn stator winding

How to determine such a malfunction is a far-reaching question. For example, when there is a short circuit of 2-3 turns in a short section, it is practically impossible to identify a defect without using a specific tool.

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

Other variations, when sufficiently remote sections are closed to each other, in principle, must be determined by a simple measurement of the resistance of the working windings of the motor stator.

Usually the winding where there is a "short", gives less resistance to other windings. However, an accurate motor circuit will be required.

Equipment Repair Tips

Split system compressor internal defects are repaired exclusively in professional workshops. At home, the forces of the owner of such complexity repair seems to be irrational, with an extremely small percentage of successful execution.

If the normal operation of the compressor is disturbed due to surplus or lack of refrigerant, the repair task can be completely resolved on its own.

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

Significant winding damage
With an interturn circuit, repairing at home is seen as a futile exercise. Such a malfunction is difficult to repair even in a professional workshop.

When the starting capacitor is the cause of compressor failure, open the top cover of the outdoor system unit by first disconnecting the machine from the power supply.

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

Conclusions and useful video on the topic

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

The operation of modern split systems shows a very long-term operation without the need for repairs. Especially when it comes to serious defects, such as inter-turn short circuit or mechanical wear.

Simple malfunctions can be repaired quite simply, and in the case of complex defects, a reasonable solution is to replace the split system with a new one. Serious repairs will force you to spend as much money as it requires purchase of a new split system.

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

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

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Visitors Comments
  1. Dmitry

    I have such a problem - the compressor does not start, and after 5 minutes the machine to which the air conditioner is connected is approximately knocked out. In this case, the voltage suitable for the outdoor unit is zero, and when one of the compressor wires is turned off, it is normal. But the case of both the compressor and the fan is cold. What could be the problem? The resistance of the compressor windings is approximately 2 ohms.

    • Expert
      Alexey Dedyulin

      Hello! The air conditioning compressor (outdoor unit) does not start working immediately when cooling starts, but after 2-5 minutes. This is normal and all compressors are arranged this way, and the higher the power of the split system, the more time elapses between turning it on and starting the fan.

      When the fan starts, the load on the wiring increases sharply, as evidenced by the resistance of 2 ohms on the windings, so it knocks out RCDs (plugs). Perhaps the matter is a poor-quality or outdated machine. Try replacing it, and if the problem persists, then you need to look for problems in the wiring or outlet.

      To verify them, you can do the following: instead of the air conditioner, connect an energy consumer of the same power and if the RCD knocks out, then the reason is precisely in the wiring.

      Please note that this mode of operation negatively affects the operation of the external unit. You must first fix the malfunction, and then operate the split system.

  2. Alexander

    Does the compressor turn on with the fan?

  3. Vitaliy

    Good day. When you turn on the air conditioner, it turns on and starts blowing, the compressor and fan turn on after 3-4 minutes, sometimes together, sometimes at first the compressor, and then the fan.

    After working for some time, especially if the sun is shining on the outdoor unit (on the street), the compressor is cut off, although the power from the indoor unit is through a relay, it is supplied to it, the fan is spinning, and the compressor is silent. If in the evening, when the sun does not shine on it, the compressor turns on and works. It does not cool very much, the pressure is low (I can’t measure high, the nozzle is only at low pressure) with the air conditioner running 5 bar.

    Thank you very much in advance for your advice.

  4. Ruslan

    Hello. When we moved from one store to another, we dismantled the air conditioner. Freon unfortunately all came out with this. When the air conditioner was installed in a new place, the compressor stopped turning on (the fan is running). We tried to change the capacitor, but it did not help (.

    Can the compressor not start because there is no freon in the system? Or do you still need to refuel first and then check? Thank.