Faced with humming, knocking or complete failure of household appliances, owners often look for an answer to the question: what is a piston refrigerator? In fact, we are not talking about a separate type of units, but about a type piston compressorthat is the heart of most modern refrigeration units. It is this unit that is responsible for compressing the refrigerant and its circulation through the system, providing the necessary cold in the chambers.
Understanding the design of this mechanism is necessary for anyone who wants to understand the causes of noise or plans to diagnose faults. Piston units have dominated the market for decades due to their reliability and maintainability, although they are inferior in noiselessness to more modern inverter analogues. In this article, we will analyze the internal structure in detail, consider typical problems and determine when self-repair is possible and when replacement of the unit is required.
The principle of operation of the piston mechanism
The main task of the compressor is to create a pressure difference in the refrigerant circuit. Unlike linear or inverter models, where movement occurs back and forth in a straight line, it uses a crank mechanism, reminiscent of the internal combustion engine of a car. The electric motor rotates the shaft, which pushes through the connecting rod piston inside the cylinder.
The freon compression process occurs cyclically. When the piston moves down, the pressure in the cylinder drops and gaseous refrigerant from the evaporator is drawn through the inlet valve. As the piston moves upward, the volume of the chamber decreases, the pressure increases, the inlet valve closes, and the exhaust valve opens, pushing the compressed gas into the condenser.
Important It should be noted that the effectiveness of this process directly depends on the tightness of the valve group and the condition of the o-rings. If valves they become deformed or burn out, the compressor stops creating the necessary pressure and the refrigerator stops freezing, although the motor itself may continue to work. This is a classic situation when “the refrigerator hums, but does not cool.”
Design features and device
A piston compressor is a sealed metal casing, inside which an electric motor and a mechanical part are located. All components are immersed in oil, which serves as both a lubricant for rubbing pairs and a coolant. Hermozone —this is the name of this sealed block—it is not intended for opening in domestic conditions without special equipment.
The mechanical part consists of a cylinder block, a crankshaft, connecting rods and pistons. In household refrigerators, one- or two-piston models are most often found. The number of pistons affects the smoothness of operation and the level of vibration: two-piston systems, where the pistons move in antiphase, are quieter and create less vibration on the housing.
Why can’t you open the casing yourself?
Inside the casing there is an inert gas or vacuum, as well as oil vapor. When opened, the tightness is broken, moisture and air get inside, which will instantly damage the compressor when turned on. In addition, there are high voltages and springs under load.
The valve group includes suction and discharge valves, which are thin elastic plates. Their condition is critical for the operation of the entire system. The design also contains shock absorbers that dampen vibrations and a system of pipes for connecting to the refrigerator circuit.
Main types of piston compressors
Despite the general principle of operation, there are several modifications of piston units that are used in various technologies. The noise level, energy consumption and service life of the device depend on the type of design. The most common are crank-yoke and crank-rod mechanisms.
In crank-rod models, which are most common, The piston is connected to the shaft through a connecting rod. This is a classic design that provides high performance, but also creates characteristic noise during operation. Crank and rocker mechanisms are considered more advanced in terms of balance, since they are better balanced.
It is also worth mentioning the division by the number of cylinders. Single-cylinder models are cheaper and simpler, but create more vibration. Two-cylinder (twin) units are more difficult to manufacture, but provide more stable pressure and a lower level of acoustic discomfort. In modern mid- and high-class models, manufacturers are increasingly using multi-cylinder circuits or switching to linear compressors.
Typical faults and their symptoms
Diagnostics of a piston compressor often begins with an analysis of the sounds it makes. Wear of parts is inevitable, and over time, gaps increase and materials lose their properties. The most common problem is wear of the connecting rod and piston groupwhich leads to knocking, especially when starting or stopping the engine.
Another common malfunction is valve failure. If the valve plate bursts or loses its elasticity, the compressor will not be able to pump freon. In this case, the refrigerator will work continuously, trying to gain temperature, but there will be no cold. In this case, the engine may overheat.
| Symptom | Probable cause | Necessary actions |
|---|---|---|
| Loud metallic knock when starting | Bearing wear or piston contact about the walls | Replacing the compressor |
| It hums, but does not cool | Failure of the valve group or leakage of freon | Pressure diagnostics, replacement of the unit |
| Warm body, motor does not starts | Seizing of the mechanism or motor windings | Checking the resistance of the windings |
| Thermal relay is triggered | Overheating due to friction or problems with the starter | Replacing the starter relay or compressor |
The situation when the compressor hums, clicks and turns off after a few seconds deserves special attention. This indicates that the shaft cannot turn. The reasons may be jammed mechanics or failure of the start relay. Start relay - this is a consumable item that often breaks before the motor itself, and replacing it is much cheaper.
Do-it-yourself diagnostic instructions
Before calling a technician or buying a new unit, you can carry out initial diagnostics. This will help you understand the scale of the problem and avoid unnecessary expenses. To check, you will need a multimeter and basic skills in working with electrical appliances.
First of all, you need to make sure the integrity of the motor windings. To do this, remove the protective casing at the back of the refrigerator, find the compressor and disconnect the start relay. Below it are three winding contacts. It is necessary to “ring” them with a multimeter in resistance measurement mode.
☑️ Checklist for checking the compressor
The normal resistance of the working winding is usually 20-40 Ohms, the starting winding is a little less. If the multimeter shows one (infinity), then there is a break. If zero - short circuit. It is also important to check the “breakdown on the housing”: none of the contacts should contact the copper tubes or the compressor housing.
⚠️ Attention: If you find that the winding resistance is normal, but the compressor does not start, the problem may be with the start relay or capacitor. Do not try to disassemble the sealed unit itself - this is only safe in factory conditions.
Noise and vibration: normal or breakdown?
Many users confuse the normal operating noise of a piston compressor with signs of breakdown. Indeed, the piston group produces characteristic sounds: the hum of the motor, the noise of circulating refrigerant and periodic clicks of the thermostat. However, these sounds should be background and not annoying.
The alarm should be sounded if the nature of the noise has changed. The appearance of ringing, rattling or strong vibration transmitted to the floor and walls indicates an imbalance or destruction of internal elements. Often the cause of rattling is not the compressor itself, but loose mounting bolts or contact of the circuit tubes with the refrigerator body.
To reduce the noise level, you can use anti-vibration stands under the legs of the refrigerator or special gaskets for the compressor (if the design allows their installation). However, if the source of noise is a knock inside the “pot”, then no external measures will help, the unit will need to be replaced.
Repair or replacement: economic feasibility
The question of “repair or replace” arises before every owner of faulty equipment. In the case of piston compressors, the answer is clear: repairing the containment zone at home is impossible. Opening the casing requires welding, evacuation of the system and precise filling with oil, which is only available in specialized workshops.
The cost of work on overhauling the compressor (replacing valves, bearings) is often comparable to the price of a new unit, and the reliability of such “repairs” is questionable. Therefore, the industry standard is to completely replace the compressor with a new one of similar power and performance.
⚠️ Attention: When replacing a compressor, it is necessary to replace the filter-drier and evacuate the system. A simple “re-soldering” of tubes without a vacuum will lead to rapid failure of the new compressor due to moisture in the system.
If your refrigerator is more than 10-12 years old, replacing the compressor may not be economically feasible, since the cost of work will be up to 70% of the price of a new refrigerator. In such cases, it is more rational to consider purchasing new equipment with a more modern and economical linear or inverter compressor.
Is it possible to supply a compressor of a different brand?
Technically, yes, if the overall dimensions, type of refrigerant and performance are the same. However, this requires recalculating the length of the capillary tube and reconfiguring the system, which only an experienced technician can do.
FAQ: Frequently asked questions
Why does a piston compressor get very hot?
Heating to 70-90 degrees is normal for a working compressor, since When gas is compressed, heat is released. However, if the case is hot to the point where you can’t touch it with your hand, or smells like burnt wiring, this is a sign of overload, a malfunction of the thermostat, or problems with ventilation of the condenser at the back of the refrigerator.
How many years does a piston compressor last?
The average life of high-quality piston compressors (for example, Secop, Danfoss, Atlant) is 10-15 years, subject to operating conditions. Chinese analogs of the budget segment may require replacement after 5-7 years of active operation.
Is it possible to replace a piston compressor with an inverter one?
Theoretically it is possible, but extremely difficult and expensive. This requires replacing the entire control system, installing an electronic module and re-soldering the circuit. It is easier and cheaper to install a new piston compressor of the same model.
What does the R600a marking on the compressor mean?
This is the type of refrigerant (isobutane) that the compressor is designed to work with. When replacing a unit, it is strictly prohibited to use a compressor designed for R134a freon for a system with R600a, and vice versa. Also, R600a is an explosive gas that requires special care during repairs.