A modern refrigerator seems to us to be a simple and understandable household appliance that simply needs to freeze, and we rarely think about the complex physical processes hidden behind its steel walls. However, it is compressor, which in everyday life is often called the engine, that is the heart of the entire system, ensuring the circulation of the refrigerant and the creation of low temperatures in the storage chambers. Understanding how this mechanism works helps owners of household appliances quickly diagnose breakdowns, distinguish a normal hum from an emergency knock, and make informed decisions about the need to call a technician or try to repair it themselves.
The fundamental operating principle is based on the constant compression and movement of gaseous refrigerant through a closed circuit of pipelines. An electric motor drives the piston group or rotates the shaft of the spiral mechanism, creating the pressure difference necessary for the phase transition of freon from gas to liquid and back. This process is accompanied by the active absorption of heat from the internal space of the refrigeration chamber and its release into the environment through a condenser located on the rear wall of the unit.
It is important to note that the efficiency of the entire system directly depends on the health of the motor-compressor, since it consumes up to 95% of all electricity used by the refrigerator. Any deviations in its operation, be it overheating of the windings, wear of mechanical parts or problems with the starting relay, immediately affect the temperature conditions inside the chambers and can lead to food spoilage. Next, we will look in detail at the internal structure, types of engines and the nuances of their functioning.
Basic structure of a motor-compressor
Structurally, the refrigerator engine is a sealed metal casing, inside which the compressor unit itself and the electric motor are mounted on a spring suspension. Such a suspension is necessary to dampen vibrations that occur during operation of the piston group, which makes operation of the device quieter and more comfortable for users. There is also oil inside the casing, which lubricates the rubbing parts and ensures the tightness of the gaps between the piston and the cylinder.
The electric motor, located in the lower part of the casing, has a rotor pressed directly onto the compressor shaft, which eliminates the need for belt drives or couplings. The motor stator is mounted on the inner surface of the casing or on special brackets, and its windings are made of copper wire with heat-resistant insulation that can withstand high temperatures. When voltage is applied to the windings, a magnetic field appears, which causes the rotor to rotate, transmitting torque to the crank mechanism.
⚠️ Attention: It is strictly forbidden to open the sealed compressor casing at home without special equipment. There may be gas under pressure inside, and moisture or dust getting inside the mechanism will instantly disable the unit.
There are three contact pins connected to the top of the casing for connecting the starting and running capacitors, as well as a thermal relay. These components are critical to starting the motor, since a single-phase asynchronous motor cannot start rotating on its own without additional starting torque. On the side or bottom there are fittings for connecting the suction and discharge pipelines through which the refrigerant circulates.
Principle of operation and cycle cooling
The operating cycle of the refrigeration unit begins at the moment when the thermostat detects an increase in the temperature in the chamber above the set value and closes the electrical circuit. Voltage is applied to the windings of the electric motor, and the rotor begins to rotate, driving the piston. A vacuum is created in the cylinder, and low-pressure refrigerant vapors are sucked in from the evaporator through the suction valve.
Next, a compression stroke occurs when the piston moves upward, reducing the volume of the working chamber and sharply increasing the gas pressure. At this point, the suction valve closes and the discharge valve opens, pushing the compressed hot gas into the condenser. It is here that, passing along a long coil on the back wall, freon gives off heat to the surrounding air and condenses, turning into a liquid.
The high-pressure liquid refrigerant passes through a capillary tube or choke, where its pressure drops sharply and it enters the evaporator inside the refrigeration chamber. There it boils at a low temperature, actively absorbing heat from the food, and turns back into gas, after which the cycle repeats. This continuous process ensures stable cold maintenance.
Types of compressor units
Modern and old models of refrigerators can use different types of compressors, each of which has its own design features and operating principles. The most common type has remained for several decades piston compressor, where gas compression occurs due to the reciprocating movement of the piston in the cylinder. Such units are reliable, repairable, but have noise and vibration levels compared to more modern analogues.
Premium-class equipment is increasingly used inverter compressors, which do not turn off completely after reaching the desired temperature, but only reduce engine speed. This allows you to avoid constant starting currents, significantly save energy and maintain temperature conditions with high accuracy. The absence of frequent start and stop cycles extends the life of the mechanical parts of the engine.
There are also rotary and scroll compressors, where compression occurs due to the rotation of the rotor or spirals. They are distinguished by their compact size, low noise level and high efficiency, but their repair is often not economically feasible due to the complexity of the design and the lack of spare parts.
| Compressor type | Noise level | Energy efficiency | Resource work |
|---|---|---|---|
| Piston | High | Average | 10-15 years |
| Inverter | Low | High | 15-20 years |
| Rotational | Medium | High | 12-18 years |
| Linear | Low | Very high | 15-20 years |
Starting system and starting relay
A special role is played in the operation of a single-phase asynchronous motor a starting device that provides initial acceleration of the rotor. Since the stator magnetic field by itself does not create the torque required for starting, an additional starting winding is used, which is phase-shifted relative to the working one. The connection of this winding is controlled by a special starting relay.
In older models, relays with a posistor are often used - a thermocouple, which heats up when current passes and opens the starting winding circuit 1-3 seconds after starting. More modern units use electromagnetic relays, where the current in the working winding creates a magnetic field that keeps the contacts of the starting circuit closed until the speed increases. As soon as the engine reaches operating mode, the current drops and the contacts open.
A faulty start relay is one of the most common reasons why the refrigerator hums but does not start. If the relay "sticks" in the closed state, the starting winding burns out due to overload. If the contacts do not close at all, the engine only hums, trying to start, but no rotation occurs, which also leads to overheating and thermal protection.
What happens when turning on and off frequently?
Frequent engine starts lead to thermal shock of the windings and rapid wear of mechanical parts, since the main wear occurs precisely at the moment of start.
Diagnostics of engine malfunctions
The malfunction of the motor-compressor can be determined by a number of characteristic signs that appear during operation of the refrigerator. The first and most obvious symptom is when the unit turns on, emits a short beep and immediately turns off, or does not respond at all when the thermostat is turned on. In such cases, a characteristic click of the relay is often heard, followed by silence or repeated attempts to start.
Another important sign is overheating of the casing the compressor. If, when touching the back wall in the area of the motor, the hand cannot withstand more than 2-3 seconds, this may indicate an interturn short circuit of the windings, the engine is operating in a “dry running” mode, or problems with the circulation of the refrigerant. The normal operating temperature of the casing is about 60-80 degrees Celsius, which is noticeably hot, but not scalding.
It is also worth paying attention to the color of the escaping gas when checking (if it is carried out by a technician) and the presence of a burning smell. The appearance of black smoke or a sharp smell of burning insulation when trying to start indicates a breakdown of the windings on the housing or between the turns. A visual inspection of the wires may show melted insulation at the contact points.
⚠️ Attention: If you smell burning or see sparking in the compressor area, immediately disconnect the refrigerator from the power supply. Further operation may result in a fire.
Inspection and testing methods
To accurately diagnose the engine condition, it is necessary to use measuring instruments, primarily a multimeter. The first step is always to check the integrity of the windings: measure the resistance between the common contact, the starting and operating terminals. Normal resistance values for different models may differ, but usually the resistance of the starting winding is higher than that of the working winding, and between the general and working windings it is minimal.
The second important stage is checking for breakdown on the housing. One multimeter probe is applied to any of the contacts, and the second is applied to the cleaned area on the metal casing of the compressor. The device should show infinity (one in the MOhm limit), any other value indicates a violation of the insulation and the need to replace the unit.
The starting relay and heat sink are also checked. You can check the relay by shaking it near your ear: if you hear the ringing of parts inside, the mechanism may be damaged. The thermal protection device should ring when cold and open the circuit when warm. A comprehensive check allows you to exclude external factors and make sure that the problem lies in the engine.
☑️ Diagnostics before calling a technician
Features of replacement and repair
Replacing a motor-compressor is a complex technical procedure that requires specialized equipment, such as a gas burner, a vacuum pump and a pressure gauge station. The process begins by disconnecting the device from the network and accessing the compressor compartment, after which the technician cuts off the copper pipelines and desolders the old unit. A new compressor is installed in its place, corresponding in power and cooling capacity.
A critically important step is evacuation of the system. After soldering all connections, it is necessary to remove air and moisture from the circuit by creating a deep vacuum. The remaining moisture can freeze in the capillary tube, forming an ice plug, or react with the oil and coolant, forming acid that will destroy the engine from the inside.
After vacuuming, the system is charged with a strictly defined type and amount of coolant, indicated on the nameplate. Overfilling or underfilling freon will lead to incorrect operation of the refrigerator and rapid failure of the new compressor. It is also necessary to replace the filter-drier, which cleans the refrigerant from contaminants.
Operation rules for extending service life
To ensure that the engine To ensure that your refrigerator lasts as long as possible, you must follow a number of simple but important operating rules. First of all, adequate ventilation of the rear wall of the unit should be ensured: the distance to the wall should be at least 5-10 cm, and the space around the condenser should not be cluttered with furniture or things. Overheating is the main enemy of winding insulation.
It is not recommended to open the doors and leave them open for a long time, as this forces the compressor to work without stopping, trying to compensate for the loss of cold. Also, do not load hot food into the chamber, which puts extreme stress on the system. Regular defrosting (for drip systems) prevents the formation of a thick ice crust, which impairs heat transfer.
Stable voltage in the electrical network also plays a crucial role. Voltage surges can damage the start relay or motor windings. To protect expensive equipment in conditions of unstable power supply, it is advisable to use voltage stabilizers or surge protectors with a surge protection function.
Why does the refrigerator hum loudly immediately after turning on?
A loud hum in the first seconds of operation is often associated with the process of starting the engine and the operation of the starting relay. If the buzzing noise subsides after 3-5 seconds, this is normal. If the sound persists or is accompanied by vibration, the shock absorbers may be worn out or there are problems with the fastening of the pipelines.
Can a compressor from a refrigerator be used for other purposes?
Yes, these units are often used to create homemade compressors for airbrushing, inflating tires or pneumatic tools. However, it must be remembered that they are designed to work with freon, and not with atmospheric air, and require modifications of the lubrication and filtration system.
What is the service life of a modern compressor?
The average service life of a high-quality piston compressor is 10-15 years, and inverter models can work up to 20 years or more if the conditions are met operation. The resource depends on the number of on-off cycles and temperature conditions.
Is it dangerous to touch a running compressor?
It is not recommended to touch a running compressor, as its temperature can reach 80-90 degrees Celsius, which can cause burns. In addition, voltage may be present on the casing in the event of an insulation breakdown, although modern safety standards minimize this risk.
What to do if the compressor is hot, but the cold does not flow?
This may indicate a freon leak or a clogged capillary tube. The engine idles, trying to pump gas, but there is no circulation. A call to a technician is required to find leaks, vacuum and refill the system.