Has your old refrigerator stopped freezing and are you ready to call a truck to dispose of it? Don't rush. Inside this bulky box hides a real technical diamond compressor that can serve for many years in the right hands. Many craftsmen underestimate the potential of this unit, sending tons of metal for melting, although it is the heart of many useful homemade products.
In fact, motor-compressor from a household refrigerator is a ready source of compressed air, capable of developing pressure up to 6-10 atmospheres, and sometimes higher, in depending on the model. Its compactness, relatively low noise level compared to industrial analogues and the ability to operate from a regular 220V network make it an ideal candidate for a home workshop. In this article we will look at how to turn unnecessary junk into a functional tool.
Before proceeding with dismantling, it is worth assessing the condition of the unit. If the refrigerator stops cooling due to a freon leak or a thermostat failure, the compressor itself most often remains fully operational. Resource such engines have tens of thousands of operating hours, so even after 10 years of service in the cabinet, it can work for the same amount of time in a new role.
The most popular and logical use of an old compressor is to create a complete one air compressor for a garage or workshop. Unlike bulky industrial units, the refrigeration unit is much quieter, which is critical for work in residential buildings or small spaces. The principle is simple: you assemble a system where a compressor pumps air into a receiver (tank), and from there the air is supplied to a pneumatic tool.
To create such an installation, you will need to find a suitable receiver. They can be an old gas cylinder, a fire extinguisher, or even the body of the same refrigerator, if you prepare it correctly. The main requirement is tightness and the ability to withstand pressure. A filter system, a moisture separator and a reducer are connected to the compressor, allowing you to adjust the output pressure for a specific task.
A self-assembled unit will allow you to use pneumatic tool: spray guns, impact wrenches, grinders and even sandblasters (with sufficient performance).
When assembling the compressor station, be sure to install check valve between the compressor and the receiver. This will prevent the reverse flow of air and oil from the tank back into the engine cylinder after stopping, which will save the mechanism from water hammer the next time it is started. Also do not forget about the pressure gauge for visual control of pressure.
⚠️ Attention: Never use containers for flammable liquids for the receiver without careful processing and checking for leaks. Air pressure in a closed volume is the potential energy of an explosion, so saving on the thickness of the tank walls is unacceptable.
Another important aspect is heat removal. When air is compressed, the temperature in the combustion chamber (relatively speaking) and at the outlet of the compressor increases significantly. Therefore, it is better to equip the outlet pipe with a copper tube rolled into a spiral (heat exchanger), or simply let it cool before entering the receiver, so as not to damage the rubber seals and hoses.
☑️ Assembling the compressor unit
If you do not need compressed air, but, on the contrary, require its absence, then the refrigerator engine easily turns into an efficient one vacuum pump. The design of the piston group allows not only to pump, but also to pump out air, creating a vacuum. This is an indispensable tool for vacuum packaging products, molding plastic products, or conducting experiments.
To implement this idea, you don’t even need a receiver. It is enough to tightly connect the hose to the inlet pipe (suction), and leave the outlet open or direct it into a container with oil to visualize the flow and lubrication. The pumping performance of such pumps is quite high for domestic needs, allowing you to achieve a deep vacuum in a matter of minutes.
However, there is a nuance: when operating for suction, moisture vapor and aggressive substances can pass through the compressor if you are pumping out more than just air. To protect the internal mechanisms, a trap (flask) is placed between the pump and the vacuum chamber, which retains liquid and vapor.
Vacuumators based on refrigeration compressors are often used to impregnate wood with protective compounds under pressure (or vacuum), which allows antiseptics to penetrate deeply into the wood structure. This is also an excellent option for those who repair office equipment or laser printers, where dust must be removed from components.
Do not forget about simpler, but no less useful applications. For example, from an old motor you can make a powerful one aerator for a large home aquarium or fish pond. Saturation of water with oxygen is critical for the life of aquatic organisms, and the performance of the refrigeration compressor is enough for a whole cascade of sprayers.
Another interesting idea is to create a pneumatic mailbox or a system for transferring small objects through pipes. Children will be delighted, and you will get a great way to practice engineering thinking. In this case, the compressor works in tandem with the valve system, creating air pulses.
The compressor can also be used for cleaning hard-to-reach places from dust. A directed jet of air will knock out dirt from keyboards, computer system units, car radiators and ventilation ducts more effectively than any can of compressed air, which, moreover, runs out quickly.
The secret of quiet operation
Why is the refrigerator compressor so quiet? Inside the casing (metal ball) there is not only the motor, but also the spring suspension of the compressor itself. The motor hangs on springs without touching the walls of the housing, which dampens vibrations. When remodeling, it is important to preserve this suspension and not tightly screw the unit to the frame without vibration supports.
For those who love extreme temperatures, the opportunity opens up to create cryogenic installation or simply a powerful cooler. The principle of operation of the refrigerator is based on the evaporation of the refrigerant, but if you remove the evaporator and direct the flow of cold air directly, you can create a local cooling zone. True, using old freon openly is now prohibited by environmental standards, but the principle of heat removal itself can be used to cool processors or other elements in experimental installations, replacing the circuit with a safe one.
A more realistic option is to use a compressor to create a plant for liquefying gases or deep freezing for scientific purposes, but this requires serious engineering training and knowledge in the field of thermodynamics. In everyday life, most often they simply make very powerful air conditioners for garages (“evaporative coolers”), using the throttling effect.
Before you start sawing and cooking, let's compare the capabilities of different types of compressors so that you understand what to expect from your homemade product. Below is a table showing approximate characteristics.
| Parameter | Refrigeration compressor | Automotive compressor | Industrial screw |
|---|---|---|---|
| Max. pressure | up to 10-15 atm | up to 7 atm | up to 15-30 atm |
| Performance | Low/Medium | Average | Very high |
| Noise level | Low (in casing) | High | Very high |
| Resource | High | Medium | Round the clock |
As can be seen from the table, refrigeration unit wins in terms of noise and the ability to create high pressure, but loses in productivity (volume of air pumped per minute). Therefore, to work with powerful pneumatic tools, such as impact wrenches or drills, one such motor may not be enough - it simply will not have time to replenish the air volume in the receiver.
However, for aerography, tire inflation, blowing and working with small volumes of air, its characteristics are more than enough. The main advantage is the ability to assemble the system “for yourself”, placing all the components compactly and conveniently specifically for your workplace.
The most difficult stage is dismantling and preparation. The compressor is mounted inside the refrigerator on a frame, often together with the condenser (grid at the back). You need to carefully cut through the copper tubes that fit the unit. Attention: there may be residual pressure inside the system, so cut the tubes carefully using side cutters or a metal file to prevent oil from splashing into your eyes.
After removing the motor, you need to determine where where is the entrance and where is the exit? Typically the tubes are located asymmetrically. The easiest way to check is to briefly plug in the compressor (observing safety precautions!) and place your finger at the ends of the tubes. Where the air blows is the exit, where it sucks in is the entrance.
Often there are plugs on the pipes. They need to be removed. If the compressor was left for a long time, oil could leak inside. This is normal for such units (the lubrication system there often splashes), but it is better to drain excess oil through the inlet, slightly tilting the housing. Also check the condition of the starting relay and capacitor - they are usually mounted on the side and covered with a plastic or metal casing.
The electrical connection diagram is simple, but requires care. Typically there are three wires coming from the motor that go into the start relay. Two of them are windings (starting and working), and the third is common. In modern models, the relay often has a terminal block into which a plug is simply stuck. If you cut the wires, it will help you multimeter for continuity.
Find the common wire (the resistance between it and the other two will be approximately the same, but less than between the starting and working windings). The working winding has more resistance, the starting winding has less. The connection diagram is standard: phase and zero go to the common and working contacts, and the starting one is connected through a capacitor (if it is in the relay circuit) or directly through the starting device.
If you are not confident in your electrical knowledge, it is better to invite a specialist or find a diagram for a specific compressor model on the Internet using the markings. Incorrect connection will lead to humming, overheating and failure of the windings. It is also strongly recommended to install protection in the power circuit, since compressors are sensitive to current overloads. thermal relay protection, since compressors are sensitive to current overloads.
⚠️ Attention: The operating pressure in the system can reach critical values. Be sure to install a safety valve (automatic pressure relief) that is set to the safe limit for your receiver. Ignoring this rule turns a homemade product into a time bomb.
During the operation of a homemade compressor, you will be faced with the need for maintenance. The main problem is condensation. When moist air is compressed, water is formed inside the receiver and tubes. If you do not remove it, it will get into the tool and ruin the paint or cause corrosion.
The solution is simple: at the lowest point of the receiver (tank) you need to weld or screw in a tap to drain the condensate. Periodically, after work, open this tap and drain the accumulated liquid. Also, do not forget to change or clean the air filter at the inlet to the compressor - dust accelerates the wear of the piston group.
The oil in such compressors is rarely changed, since the system is virtually sealed, but if you notice that the unit has begun to “spit” oil into the outlet pipe, the oil level in the crankcase may be too high or the piston rings have worn out. In the first case, excess oil must be pumped out through the inlet hole with a syringe.
Oil question
Many people ask what kind of oil to pour into the compressor? You cannot pour regular motor oil there - it foams and clogs the channels. You need special compressor oil. But often in household homemade products they make do with what is left inside from the factory, simply controlling its level and color.
There is a myth that a compressor from a refrigerator can replace a professional unit for a service station. This is wrong. Its productivity (usually 30-50 liters per minute) is too low for continuous operation of pneumatic tools. It is good for “jerk” work: pumping, pumping, blowing.
Also, do not forget about the environmental component. If you are removing a refrigerator for a compressor, make sure that the refrigerant (freon) has been professionally removed and not released into the atmosphere. The ozone layer will thank you, and you will avoid problems with the law, since freon emissions are strictly regulated in many countries.
Use the potential of old equipment wisely. The engine from a refrigerator is not just a piece of metal, but a ready-made module for creative technical solutions, which, with a competent approach, will serve you faithfully for many years, saving your budget and delighting with new opportunities.
How many atmospheres can a compressor from a refrigerator produce?
Standard household compressors (models like SK, KV and their analogues) are capable of creating a discharge pressure of up to 15-25 atmospheres in a closed system, however, the operating range is usually limited to 6-10 atmospheres due to the design of the valves and motor power. For domestic needs, this is more than enough.
Is it necessary to change the oil in the compressor during refurbishment?
If the compressor was taken from a working refrigerator, the oil inside is usually in good condition. It only needs to be changed if the unit has been sitting for a long time with the pipes open (it has picked up moisture) or if you notice that it is overheating greatly and is leaking oil. In this case, washing and replacing with fresh compressor oil will extend the life of the device.
Can such a compressor be used for airbrushing?
Yes, this is one of the best solutions for airbrushing. The compressor provides stable pressure without pulsation (if there is a receiver), which is critical for even paint application. The main thing is to install a high-quality moisture separator and a reducer with a pressure gauge for fine-tuning the pressure (usually 0.5-2 atm).
Why does the compressor hum but not pump?
Most often the reason is a break in the starting winding, a malfunction of the starting relay or a wedge of the piston group due to lack of oil or moisture. It is also possible that the tightness of the valves inside the compressor head is broken, and it simply moves air back and forth without creating pressure.