A compressor failure in an air conditioner leads to a complete stop of the cooling process, since it is this unit that ensures the circulation of the refrigerant in a closed circuit. If you hear an extraneous knock when starting the split system or notice that the indoor unit fan is running, but no cold air is flowing, the problem most likely lies in the mechanical or electrical part of the blower. Without proper compression of freon vapor, condensation of gas into liquid is impossible, which is a key stage of heat exchange in any refrigeration machine.
The main task of the device is to take low pressure refrigerant gas from the evaporator and compress it to high pressure, sending it to the condenser. Working principle of the air conditioning compressor is based on the laws of thermodynamics, where changes in the volume of the working chamber directly affect the pressure and temperature of the substance. When compressed, the temperature of the gas increases sharply, which allows it to effectively transfer heat to the environment through the radiator of the external unit.
Modern models of climate control technology use various design solutions to implement this process, from classic piston mechanisms to high-tech spiral units. Understanding exactly how this “heart” of the system functions is necessary for correctly diagnosing faults and selecting equipment with optimal energy consumption. In this material we will analyze in detail the physics of the process, types of drives and the reasons why a unit may fail.
The physics of the refrigerant compression process
The refrigeration cycle begins with the refrigerant entering the compressor in a state of saturated vapor at low temperature and low pressure. The mechanism of the device creates a pressure difference, forcing the substance through the pipeline system. Gas compression leads to a significant increase in its temperature, turning the steam into a superheated gas that can condense even at high outside temperatures.
The effectiveness of this stage directly affects the overall performance of the system. If the compressor is unable to create sufficient outlet pressure, the cycle is disrupted and heat exchange in the condenser becomes impossible. It is important to consider that during operation, the refrigerant is also mixed with compressor oil, which circulates through the system to lubricate the rubbing parts.
⚠️ Attention: Liquid phase of refrigerant entering the compression chamber (water hammer) can instantly destroy valves or spirals, since liquids are practically incompressible.
To understand the scale of the loads, it is worth noting that the pressure on the discharge side can reach 25-30 atmospheres, while on the suction side it is often below atmospheric (vacuum). Such a colossal difference requires tightness and high mechanical strength of all components. Thermodynamic cycle closes only if the discharge element is operating stable.
Temperature operating conditions
The temperature inside the compressor can reach 100-120 degrees Celsius, which requires efficient heat removal. Overheating of the motor windings or mechanical parts is one of the main reasons for the operation of a thermal protection relay.
Structure and design of main types
The climate control equipment market is dominated by several types of structures, each of which has its own service characteristics and service life. The most common are rotary and spiral models, which are gradually replacing outdated piston analogues in the household segment.
Rotary compressors, often used in wall-mounted split systems, operate on the principle of rotating a roller inside a cylinder. An eccentrically mounted rotor is pressed against the cylinder wall, creating crescent-shaped chambers of variable volume. Rotary mechanism features fewer moving parts, which reduces vibration and noise levels compared to piston counterparts.
Spiral units (scroll) are considered more advanced and quieter. Compression occurs between two spiral plates, one of which is stationary, and the other performs orbital movements. This design ensures a continuous compression process without the pulsation characteristic of other types. Scroll compressor less sensitive to liquid ingress, but critical to the cleanliness of the system and the presence of oil.
The main advantage of scroll compressors is the absence of valves on suction and discharge, which reduces aerodynamic drag and increases energy efficiency.
In industrial installations, piston and screw units can still be found. Piston engines operate on the principle of an internal combustion engine, where the piston moves up and down, opening and closing valves. Screw ones use two complex-shaped rotors, which, rotating in opposite directions, move gas from the suction port to the discharge port.
Electrical and motor control
The drive for the mechanical part is an electric motor, which in most household models is asynchronous. Power is supplied to the stator windings, creating a rotating magnetic field that drags the rotor along with it. Electric motor and a mechanical compressor are often enclosed in a common sealed housing, immersed in refrigerant and oil, which keeps them cool and lubricated.
The shaft rotation speed can be controlled in various ways. In classic On/Off systems, the engine runs only at full speed, turning on and off according to the thermostat signal. Inverter systems use a frequency converter that smoothly changes the frequency of the current supplied to the windings, adjusting performance.
Using an inverter allows you to avoid starting currents, which are 5-7 times higher than the rated ones, and maintain the temperature with high accuracy. Frequency regulation also reduces wear on mechanical parts by eliminating constant start and stop cycles.
To protect the electrical part, a thermal relay is built into the housing, which opens the circuit in case of critical overheating. This can happen due to power surges, operation under extreme conditions, or a lack of refrigerant, which cools the windings in a vapor state.
The role of oil in the lubrication system
Not only refrigerant circulates inside the sealed circuit, but also special compressor oil. It is necessary to lubricate bearings, rubbing pairs and seal gaps between moving parts. No oil mist mechanical wear would occur in a matter of minutes of work.
The oil must have the following properties: it must be miscible with the coolant, have a suitable viscosity at different temperatures and have dielectric properties as it is in contact with the motor windings. The type of oil (mineral, polyester POE, polyalphagen PVE) strictly depends on the type of freon used (R22, R410A, R32).
One common problem is oil “hijacking,” when it gets stuck in remote areas of the route and does not return to the compressor crankcase. This leads to oil starvation. To prevent this, oil lifting loops are installed in long routes, and oil return procedures are built into control algorithms.
⚠️ Attention: When refilling the air conditioner, it is strictly forbidden to mix oils of different types, as this can lead to the formation of acids and destruction of the winding insulation.
Visual monitoring of the oil level in hermetic compressors is impossible without opening it, so technicians rely on indirect signs: the presence of oil stains at pipe joints, the color of the oil during evacuation, or vibration analysis.
Fault diagnosis and symptoms
The condition of the compressor can be determined by a number of external signs and parameter measurements. A humming noise that turns into a metallic clanging sound often indicates bearing or valve failure. If the compressor hums but does not start, the rotor may be jammed or the starting winding may be burned out.
An important diagnostic parameter is current consumption. If current consumption significantly below the nominal value, this may indicate a loss of performance (valve wear) or a lack of freon. Exceeding current indicates an overload, mechanical jamming or electrical problems.
☑️ Primary diagnostics of the compressor
Another symptom is overheating of the case. If your hand does not tolerate touching the metal part of the case (temperature above 90-100°C), this is an alarming sign. However, for some operating modes (for example, heating in cold weather), high heating may be normal, but requires control.
Table of main parameters and comparison of types
For a visual comparison of the characteristics of various types of superchargers used in household and semi-industrial systems, we present a summary table. These parameters help to understand why certain models are chosen for some tasks and others for others.
| Parameter | Rotary | Spiral | Piston |
|---|---|---|---|
| Noise level | Low | Very low | High |
| Resource (hours) | 15 000 - 25 000 | 30 000+ | 10 000 - 15 000 |
| Efficiency (COP) | Medium/High | High | Low/Medium |
| Sensitivity to liquids | High | Average | High |
The table shows that scroll compressors are superior in terms of service life and noise, but they are more expensive to manufacture. Rotary units have become the standard for mass-produced wall-mounted split systems due to the balance between price and quality. Piston engines are becoming a thing of the past in the household segment, remaining a niche solution.
When choosing an air conditioner, pay attention not only to the brand, but also to the compressor manufacturer. Market leaders are Toshiba, GMCC, Hitachi and Copeland.
Prevention and service life extension
In order for the compressor to serve the entire period declared by the manufacturer, it is necessary to follow the operating rules. The main condition is regular maintenance of the external unit. Contamination of the condenser heat exchanger with lint and dirt leads to an increase in condensation pressure, which sharply increases the load on the supercharger.
It is also important to avoid operating the air conditioner for heating at temperatures below the permissible limit specified in the instructions, unless a winter kit is installed. Working “at the limit” leads to freezing and water hammer. The most common cause of failure is not a manufacturing defect, but improper installation and lack of cleaning.
If you notice that your air conditioner is getting louder, cooling worse, or consuming more electricity, don’t delay calling a specialist. Early diagnosis can save an expensive component from complete replacement. A preventive inspection once a year before the summer season is the minimum necessary measure to preserve equipment.
What to do if the compressor does not start?
First of all, check for voltage at the terminals. If there is voltage, but there is silence, the start capacitor may have burned out (in older models) or the internal protection has tripped. If you hear a hum, the mechanism may be jammed. In any case, independent repair of the sealed unit is impossible; replacement of the unit is required.
Is it possible to replace the compressor with an analogue one?
Technically, yes, but it requires high qualifications. It is necessary to select a model with similar cooling capacity, type of refrigerant, overall and connection dimensions. A complete flushing of the system, replacement of the filter drier and evacuation are also required.
Why does the compressor turn on and then turn off immediately?
This is a sign that the thermal protection relay has tripped. Reasons: overheating due to a dirty capacitor, malfunction of the external unit fan, power surges in the network or an internal short circuit in the windings.