Creating a functional and productive compressor from an old refrigeration unit is a classic task for a home craftsman, allowing you to get a powerful tool with minimal financial investments. Motor-compressor, extracted from a failed refrigerator, has a unique feature: it is capable of pumping air under pressure of up to 6-10 atmospheres, while remaining almost silent. Unlike loud piston factory analogues, such devices are ideal for work in a garage or workshop, where acoustic comfort is important.
The main idea of the modification is to change the lubrication and cooling system, since normally freon compressors operate in a closed circuit with freon and oil, but when pumping atmospheric air they require other conditions. You will need not only yourself unit, but also a well-chosen container for the receiver, a filtration system and reliable automation. Correct assembly of all components guarantees a long service life and stable pressure in the pneumatic system.
In this article we will analyze in detail each stage of transforming an old household appliance into a professional tool. You will learn how to properly prepare receiver, install check valves and configure pressure switch. We will pay special attention to safety issues, since working with high air pressure requires strict adherence to technological standards and accuracy during installation.
Preparation of equipment and selection of components
The first step is to remove the compressor from the refrigerator and its primary diagnosis. Typically the unit is secured to the lower rear of the refrigerator compartment using four spring hangers or rigid bolts. Before disconnecting the pipes, make sure that the unit is de-energized and that the refrigerant (if any remains) is safely released in a well-ventilated area. To work, we need a working motor, which, when plugged into the network, emits a characteristic hum and creates a vacuum on the suction tube.
The key element of the future installation will be a receiver - a container for storing compressed air. Old propane gas cylinders, 50-liter fire extinguishers, or even casings from various fire extinguishing systems are often used as a base. Receiver performs two important functions: it stabilizes the pressure in the system, eliminating flow pulsations, and promotes air cooling, as a result of which some of the moisture condenses and settles at the bottom of the container.
It is also necessary to prepare components for piping in advance: copper or steel tubes, high-pressure hoses, clamps, pressure gauge and reducing valve. Don’t forget about the oil separator filter, which will protect the pneumatic tool from the oil emulsion that inevitably forms during operation of the piston group. All threaded connections must be sealed with fum tape or anaerobic sealant designed for high temperatures and pressure.
⚠️ Attention: It is strictly forbidden to use containers that previously contained flammable liquids (gasoline, diesel) as receivers, without thoroughly steaming and cleaning. Residual vapors can create an explosive mixture when air is compressed.
Modernization of the lubrication system and intake filtration
The standard design of a refrigeration compressor assumes that the oil is in the crankcase and is sprayed by the crankshaft, lubricating the rubbing vapors, and then condenses along with freon. When working with atmospheric air, oil will be carried into the receiver and then into the pneumatic line, which is unacceptable. Therefore, the first step is to organize an external oil catcher or switch to a system with an external oil supply, if the design allows, although for domestic needs they often simply install a powerful filter at the outlet.
An air filter must be installed on the inlet pipe (suction). It protects the insides of the mechanism from dust, which acts as an abrasive, quickly destroying the bearings and piston group. As a filter, you can use a car air filter or a homemade design with padding polyester, but it is better to use ready-made solutions from compressor equipment. The filter should be easily accessible for regular cleaning or replacement.
An important point is the oil level in the crankcase. If you do not change the design to an open one, then the oil level is controlled through a standard eye or dipstick (if provided by the model). During prolonged operation of air compression, the housing temperature may rise, so it is recommended to provide forced cooling or take breaks in operation in accordance with the technical regulations for a specific engine model.
Can compressor oil be used?
Yes, it is advisable to fill in specialized compressor oil, which foams less and has a higher flash point. However, many craftsmen successfully use high-quality motor oil, changing it more often than usual.
Manufacturing and preparing a receiver
Preparing an air container requires care and compliance with safety measures. If you are using a used gas cylinder, it must be emptied of any remaining gas, the valve turned off and rinsed several times with water. Then a hot alkali solution (for example, washing powder or caustic soda) is poured inside to remove the smell of the odorant (mercaptan), which is added to the gas to detect leaks.
After washing and drying, it is necessary to drill holes in the cylinder and weld threaded fittings (nipples). The minimum set of holes includes: air inlet from the compressor, air outlet to the consumer, a hole for a pressure gauge, a hole for a pressure switch and a hole at the lowest point for draining condensate. Welding work must be carried out by a qualified specialist, since the quality of the seams directly affects the safety of operation.
For visual control of the oil level (if the system is open) or simply for aesthetics, the cylinder is often painted with heat-resistant paint. Also at this stage, a pipe with a ball valve for draining condensate is welded to the bottom of the receiver. The presence of this tap is critically important, since water accumulating at the bottom causes corrosion of the metal and can lead to rupture of the container when it freezes in winter.
| Component | Function | Material |
|---|---|---|
| Receiver | Accumulation and stabilization of pressure | Steel (gas cylinder) |
| Pressure switch | Automatic on/off | Plastic/Metal |
| Reverse valve | Protection against reverse air flow | Brass/Bronze |
| Pressure gauge | System pressure control | Metal housing |
Assembling a pneumatic circuit and installing automation
Assembling the pneumatic part begins with installing a check valve between the compressor outlet and the receiver. This element prevents the backflow of compressed air from the cylinder into the engine after it has stopped, which facilitates restarting and protects the piston group from overload. Without a check valve, the engine may not start under pressure or even fail.
Next, pressure switch (pressostat) is installed. This device automatically opens the electrical circuit when the pressure in the receiver reaches the upper limit (usually 6–8 atm), and closes it when the pressure drops to the lower limit (about 4 atm). The connection is made into the break in the compressor power cable. On the relay body there are usually adjusting screws for adjusting the pressure delta.
The installation of the pressure gauge and reducer completes the assembly. The pressure gauge shows the current pressure in the system, and the reducer allows you to reduce the operating pressure to that required for a specific tool (for example, an airbrush needs 2-3 atm, and for a tire service - 4-6 atm). All connections are made through adapters and fittings, which must be securely tightened.
☑️ Checking the assembly of the pneumatic system
Electrical part and safety settings
The electrical circuit of a homemade compressor is relatively simple, but requires care. Power is supplied through a circuit breaker designed to handle the motor's starting current (which can be 3 to 5 times the operating current). Grounding is required since the housing is metal and operating conditions may be damp. Connection diagram: network -> automatic -> pressure switch -> engine.
Some compressor models have a starting winding and a starting capacitor. When remaking, it is important to preserve the standard electrical circuit of the motor, without mixing up the contacts of the starting and operating windings. If the engine hums but does not start, the starting capacitor may be faulty or the contacts in the relay are stuck (if it is internal, as opposed to an external pressure switch).
⚠️ Attention: Follow safety precautions when working with electricity. All connections must be insulated, and the cable must have a cross-section suitable for the current load of the motor. Use sockets with grounding.
The final stage of setup is to check the system under pressure. After turning on for the first time, listen to the system for leaks (characteristic whistle). A soap solution will help identify even microscopic holes in connections. Make sure that when the maximum pressure is reached, the relay clearly turns off the engine, and when bleeding air, turns it on again.
Maintenance and operation
A homemade compressor, like any mechanism, requires regular maintenance. The main enemy of the system is moisture in the air. After each work session or at least once a week, it is necessary to open the bottom tap of the receiver and completely drain the accumulated condensate. Ignoring this procedure will lead to rapid corrosion of the cylinder from the inside.
You should periodically check the oil level (if the design allows) and the condition of the air filter at the inlet. A clogged filter causes the engine to work overload, trying to suck air through the resistance. Also check the tension of the belts (if a belt drive is used) or the vibration mounts of the motor, which may lose elasticity over time.
When storing the compressor in an unheated room in the winter, make sure that there is no water left in the receiver and tubes, which can tear the metal when frozen. To extend the service life, it is recommended to change the oil in the crankcase (if possible) every 500–1000 operating hours, using only brands recommended by the manufacturer.
What pressure can a compressor develop from a refrigerator?
Standard refrigeration compressors are capable of creating pressure up to 10–15 atmospheres and higher, however, for safe and long-term operation of a home-made installation, it is recommended to limit the upper threshold of relay operation to 6–8 atmospheres. This reduces the load on the engine and reduces the risk of broken connections.
Is it necessary to change the oil in the compressor during modification?
If you do not open the crankcase and do not change the design to an open one, then the oil does not need to be changed and is not even possible, since access to it is closed. In closed refrigerator systems, oil is filled for the entire service life. Problems with lubrication can be solved by installing high-quality oil separator filters at the outlet.
Why does the compressor get very hot during operation?
Heating the housing to 60–90 degrees Celsius is normal for piston compressors, since the gas heats up during compression. However, if the heating is excessive, check the cleanliness of the cooling fins, the operation of the fan (if any) and the absence of leaks causing the motor to run continuously.