Opening the old hermetic compressor is not just a way to extract valuable non-ferrous metal, but also an excellent opportunity for engineers, students and home craftsmen to study the principles of operation of piston systems. The inner world of this unit is hidden from view behind a durable steel shell, but this is where the main process of compressing the refrigerant takes place, which ensures the cold in your chamber. Understanding how the components are arranged inside helps diagnose malfunctions and assess the suitability of the part for secondary use.
When you dismantle the casing, you will be faced with a complex mechanical system operating in an oil bath. The basis is electric motor, which drives the crank mechanism. Despite the apparent simplicity of appearance, the internal layout requires precise balancing and clearance. Any part, be it a suspension spring or a copper tube, performs a strictly defined function in the overall cooling cycle.
In this article we will analyze in detail the anatomy of the device so that you can confidently determine the condition of the components. Knowledge of the design allows you to distinguish a working unit from a “dead” one even before connecting to the network. Let's consider each element separately, paying attention to the materials and the physical principles of their interaction.
The design of the external casing and the suspension system
The first thing that catches your eye when disassembling is a durable steel body, divided into two hemispheres. This sealed casing is necessary to create a closed circuit that prevents freon leakage and moisture from entering the system. The housing walls often have a double structure or special ribs, which not only increases strength, but also helps cool the oil and reduce the noise of the operating mechanism. There is high pressure inside the housing, so the welds are made with special care.
The engine itself and the compressor group are not rigidly attached to the walls. They are suspended on special springss that dampen vibrations. If the motor were tightly secured, the vibration would be transmitted to the body and then to the floor, creating an unbearable roar. Typically three or four springs are used, located around the perimeter of the inner frame. Their condition is critical: if the spring bursts or jumps off, the compressor will operate with a strong knock.
⚠️ Attention: When opening the casing with a grinder or hacksaw, be extremely careful. Residual pressure may remain inside, and metal shavings should not get into the precision cylinder assemblies.
There is also a system of tubes inside through which freon moves. Suction pipe usually it goes directly into the casing cavity, where the gas is cooled as it passes by the engine windings. The discharge pipe, on the other hand, often has a more complex trajectory as the gas is supplied at high pressure to the condenser. It is important to note that there is nothing superfluous inside the case - every millimeter of space is used for effective heat exchange.
Electric motor: rotor, stator and windings
The heart of the unit is asynchronous electric motor. It consists of a stationary stator and a rotating rotor. The stator is made of thin plates of electrical steel, which is necessary to reduce eddy current losses. There are two main windings wound on the stator: starting and working. The starting winding has a higher resistance and a smaller number of turns; it is turned on only at the time of startup.
The rotor, or “squirrel cage,” is a set of plates with aluminum or copper rods. It is this part that rotates, transmitting torque to the compressor shaft. The shaft is pressed into the rotor and comes out through a special seal. Quality winding insulation plays a decisive role: if the varnish overheats or is damaged, an interturn short circuit will occur and the engine will burn out. There is always a special oil inside the casing, which not only lubricates the rubbing parts, but also cools the windings.
- 🔌 Working winding - consumes the main power in normal operation.
- 🚀 Starting winding - creates the initial torque and is turned off by a centrifugal switch or relay.
- ⚙️ Squirrel-cage rotor has no brushes and commutator, which ensures high reliability.
Interestingly, the motor shaft passes through the entire unit, being the axis of rotation for the crank. The shaft seal is one of the most difficult parts of the design, as it must hold pressure and keep oil out while remaining sealed for decades. In older models, seals of a special design were often used, in new ones - more modern materials based on fluorine rubber.
Crank mechanism and piston group
The transformation of the rotational movement of the shaft into the translational movement of the piston is carried out by crank mechanism. A crank (or connecting rod assembly with shaft) is eccentrically fixed to the engine shaft. As the shaft rotates, the crank moves in a circle, pushing the connecting rod up and down. The connecting rod, in turn, is connected to a piston, which performs reciprocating movements inside the cylinder.
The cylinder itself is made with microscopic precision. The gap between piston and the cylinder wall is minimal to ensure compression, but the piston should not jam. Grooves for piston rings can often be seen on the side of the piston, although many modern hermetically sealed refrigerator compressors use pistons without rings, where tightness is ensured by precise lapping and an oil film. This simplifies the design and reduces friction.
The materials here are selected to withstand millions of load cycles. Connecting rods are often made of silumin or cast iron, and pistons are made of aluminum alloys. The most important element is the connecting rod pin, which connects it to the piston. Intense friction occurs in this unit, so the oil supply here is organized through special channels inside the shaft or connecting rod.
Why are pistons sometimes made without rings?
In low-power refrigeration compressors, the gap between the piston and the cylinder is made so small (several microns) that the oil film itself provides the necessary tightness. This reduces friction losses and simplifies the design.
Valve system and gas distribution
Located at the end of the cylinder valve plate (or plate valve). This is the thinnest steel part in which holes are cut for suction and injection of gas. Reed valves are installed above these holes. The principle of their operation is ingeniously simple: they open only in one direction under the influence of pressure differences. When the piston goes down, the pressure in the cylinder drops, and the suction valve (lobe) opens slightly, letting in freon vapor.
When the piston starts moving up, the pressure increases sharply. The suction valve closes and the discharge valve opens, releasing the compressed gas into the discharge tube. These petal valves work at a huge frequency (50 times per second at 50 Hz), so the material from which they are made (often special spring steel) should not tire. The slightest crack or deformation of the petal leads to a drop in performance or complete failure of the compressor.
Gasks are often installed between the valve plate and the cylinder head, which ensure tightness and set the volume of dead space. Dead space is the volume that remains in cylinder when the piston is at the top. The smaller it is, the higher the efficiency of the compressor, since less compressed gas remains inside and is not pushed out.
Oil system and lubrication of rubbing parts
Unlike car engines, there is no oil pump in the usual sense. Lubrication is carried out by splashing and under the influence of centrifugal forces. There is always refrigeration oilat the bottom of the casing. The oil level is strictly regulated: if there is little of it, the piston will jam; if there is too much, the oil will begin to be carried away into the system with freon, clogging the heat exchangers.
A spiral channel is often made inside the engine shaft. When the shaft rotates, the oil rises through this channel upward to the bearings and connecting rod pin. This ensures lubrication of the most loaded ones