Converting an old refrigeration unit into a full-fledged vacuum compressor is a classic task for a home workshop, allowing you to get a powerful tool for vacuuming, airbrushing or pneumatics almost free of charge. The main advantage of such a homemade product lies in the durability of the piston group, which is designed for continuous operation for decades, and in the low noise level compared to factory counterparts. If you have a decommissioned refrigerator in your dacha or garage, it will become the heart of your new installation. Compressor However, simply pumping freon and creating a vacuum are processes with different physics of valve operation that require a careful approach to modernization. You will have to not only connect the hoses, but also completely rework the lubrication system, since the standard design is not designed to take air from the atmosphere. In this article, we will analyze in detail the process of transforming a household unit into a professional tool, paying special attention to the nuances that beginners often miss. compressor will become the heart of your new installation.
However, simply pumping freon and creating a vacuum are processes with different physics of valve operation that require a careful approach to modernization. You will have to not only connect the hoses, but also completely rework the lubrication system, since the standard design is not designed to take air from the atmosphere. In this article, we will analyze in detail the process of transforming a household unit into a professional tool, paying special attention to the nuances that beginners often miss.
Selection of equipment and diagnostics of an old unit
Before starting disassembly, you need to make sure that the donor is in good working order. The ideal candidate is considered hermetic compressor from Soviet-made refrigerators or modern models with linear motors, although the latter require more complex electronics. Visually inspect the housing for deep corrosion, especially in the lower part where condensation accumulates. Rust may indicate that moisture has already gotten inside, which will lead to rapid failure of the windings.
Check the electrical part by ringing the windings with a multimeter. The resistance between the starting and operating windings, as well as between each of them and the housing, must be within normal limits, without signs of a short circuit. If the unit hums but does not start, the piston group may be jammed or the start relay may be faulty. For a vacuum compressor, the absence of internal mechanical damage is critically important, since under vacuum even the slightest play of the valves will become noticeable.
It is also important to determine the type of refrigerant for which the system is designed, although this is secondary for working with air. The main thing is to make sure that the pipes are not broken and that metal shavings do not fall out of them when shaking. The presence of chips is a sure sign of destruction of the cylinder-piston group, and it is better to immediately send such a unit for scrap.
⚠️ Attention: Never try to open the sealed compressor casing with a grinder or a hacksaw. There are flammable oil vapors inside and a spark may cause an explosion. Disassembly is possible only after complete removal of the refrigerant in a well-ventilated area.
Necessary tools and consumables
For high-quality assembly, you will need not only the compressor itself, but also a number of additional components, without which the system will not function stably. The basis of the design will be receiver a container for compressed air, which is often used as old fire extinguishers, gas cylinders or receivers from trucks. The volume of the receiver directly affects the smoothness of the flow and the frequency at which the engine is turned on.
In addition to the container, you will need components for the pneumatic system: check valves, safety valve, pressure gauges, fittings and high-pressure hoses. Pay special attention to the material of the tubes: the standard copper tubes of the refrigerator are fragile and are not suitable for external wiring; it is better to replace them with flexible hoses or steel pipes. You will also need oil that is compatible with rubber seals and does not form carbon deposits.
- 🛠️ A drill or screwdriver with a set of metal drills for preparing holes in the receiver.
- 🔧 A set of wrenches and screwdrivers for installing fittings and electrical equipment.
- 📏 Tape measure and marker for accurately marking the mounting locations of the unit.
- 🔌 Starting relay (standard or universal) and a capacitor for starting.
Don't forget to prepare the materials to create the base. The compressor vibrates during operation, so it needs a sturdy frame. Often a sheet of plywood with a thickness of at least 20 mm or a welded structure from a corner is used. Between the metal of the compressor and the frame, it is necessary to lay vibration-isolating gaskets rubber or dense linoleum.
Dismantling and preparing the compressor
The process of removing the unit from the refrigerator begins with cutting copper tubes at a distance 10-15 cm from the body. This will allow you to save the length of the pipes for subsequent diagnostics and connection. Before turning off the power, make sure that the refrigerant is completely removed from the system by pumping it in a well-ventilated area or through a long hose outside.
The next step is to clean the body of dirt and old paint if you plan to paint it. Pay special attention to the area around the pipes. You need to determine which one is suction and which is pressure. To do this, briefly apply voltage to the unit (observing safety precautions) and bring your finger to the holes: where it blows is the exit, where it sucks in is the inlet.
It is important to note that in order to work as a vacuum pump, the standard lubrication system, which operates by spraying oil from the crankcase, may require modification. In normal mode, the oil is located at the bottom of the casing, and when working to suck in atmospheric air, it can begin to actively escape through the outlet pipe if proper drainage or return is not organized.
⚠️ Attention: When working with 220V electricity, strictly follow safety rules. All connections must be insulated and the compressor itself must be grounded. Do not touch the metal parts of the unit while it is operating.
Modernization of the lubrication system and valves
The most critical point in the remodeling is the organization of lubrication. A standard refrigerator operates in a closed circuit, and the oil circulates along with freon. When pumping out air, the oil will be carried away in the form of a mist, which will lead to a rapid drop in the level and scuffing of the piston. There are two main solutions: installing an oil separator at the outlet or switching to a system with forced lubrication. The simplest option is to install an oil trap (cyclone) immediately after the discharge pipe. This is a container with a tangential inlet, where the flow swirls and heavy drops of oil settle on the walls, flowing back. However, for long-term operation, it is better to consider the option of supplying oil directly to the friction zone through a dropper or wick, if the design allows access to the insides without violating the tightness of the casing. oil separator at the outlet or switching to a system with forced lubrication.
The simplest option is to install an oil trap (cyclone) immediately after the discharge pipe. This is a container with a tangential inlet, where the flow swirls and heavy drops of oil settle on the walls, flowing back. However, for long-term operation, it is better to consider the option of supplying oil directly to the friction zone through a dropper or wick, if the design allows access to the insides without violating the seal of the casing.
It is also worth checking the condition of the petal valves. To create a deep vacuum, the gaps must be minimal. Sometimes craftsmen carefully polish the valve seats on the glass with GOI paste, achieving a perfect fit. This increases the performance of the pump, but requires pinpoint precision.
If you plan to use the compressor specifically as a vacuum cleaner (for vacuuming bags, molding), it makes sense to think about replacing oil with synthetic one with low volatility, since mineral oil in a deep vacuum begins to actively evaporate, polluting the system and losing its properties.
Making a receiver and piping
The receiver functions as a buffer, smoothing out pressure pulsations and accumulating air volume. Before using any container (fire extinguisher, cylinder), it is necessary to pressure test it with water under pressure 1.5-2 times higher than the working pressure. This will eliminate the risk of explosion due to the accumulation of compressed air.
At the top of the receiver (if it is vertical) or at the end (if horizontal) holes for fittings are drilled. The minimum set includes: inlet from the compressor, outlet to the consumer, installation of a pressure gauge, safety valve and drain valve for condensate at the bottom. Welding work cannot be carried out on the tank; all connections are made with threaded fittings.
The compressor piping includes the installation of a check valve between the compressor and the receiver. It prevents the reverse flow of air from the receiver to the compressor after stopping the engine, which makes restarting easier and protects the piston group from water hammer.
Assembling the electrical circuit and starting device
Connecting electrical wiring requires an understanding of the operation of the start relay. Most refrigeration compressors use a PTC relay or an electromagnetic start relay. The connection diagram is usually printed on the terminal box cover or on the relay itself. An error in connecting the windings can lead to the engine burning out in a few seconds.
To automate the process, you can install a pressure switch (pressostat), which will turn off the motor when the set pressure in the receiver is reached and turn it on when it drops. This will significantly extend the life of the installation and make working with it comfortable. The pressure switch is connected to the phase break before the start relay.
Don't forget about protection: a circuit breaker corresponding to the compressor's current consumption (usually 6-10A) must be included in the power circuit. It is also recommended to install a thermal relay, if it is not built into the standard circuit, to protect against overheating of the windings during long-term operation.
☑️ Check before the first start
Testing and adjusting performance
It is better to perform the first start without connecting to the receiver, simply checking the operation on suction and blowing. Place your finger on the inlet pipe - it should fit tightly. At the outlet pipe, check for the presence of oil mist: if oil flies abundantly, the separation system is not working effectively enough.
After connecting to the receiver, note the time during which the compressor pumps up pressure from 0 to 6 atmospheres. This will allow you to evaluate the real performance of the system. For domestic needs, the normal time to fill a 50-liter receiver is 2-4 minutes. If the process takes too long, check the tightness of the connections.
During operation, monitor the temperature of the case. Hermetic compressors are cooled by freon, but when operating in air the cooling is worse. Heating up to 80-90 degrees is allowed, but if the casing becomes hotter, it is necessary to organize forced blowing with a fan or take breaks in operation.
| Parameter | Normal mode (Refrigerator) | Compressor mode (Air) | Recommendation |
|---|---|---|---|
| Working pressure | up to 15-20 atm (freon) | up to 8-10 atm (air) | Do not exceed 8 atm for safety |
| Lubricant | Circulating (freon + oil) | Splashing / Wick | Check the level every 5 hours |
| Temperature | 40-50 °C | 70-90 °C | Heating control required |
| Input humidity | Absent (dry circuit) | Atmospheric | Required filter drier |
⚠️ Attention: The operating conditions of a homemade compressor differ from the factory ones. Performance and life may vary depending on build quality and environmental conditions. Always have a fire extinguisher and personal protective equipment on hand.
Why does the compressor heat up more in air?
In the refrigerator, the refrigerant (freon), passing through the system, actively cools the motor-compressor. When operating in air, this cooling effect is absent, and air compression is a more energy-intensive process that generates more heat. Therefore, overheating is a normal phenomenon that requires control.
Frequently asked questions and troubleshooting
Why does the compressor hum but not pump?
Most likely, the problem is in the valve group (the valve plate has burst) or in the lack of tightness of the connections. It is also possible that the piston may jam due to lack of lubrication. Check if the inlet filter is clogged.
Which oil is best to fill?
Use special compressor oils (for example, KS-19 or analogues for refrigeration compressors). Automotive motor oils can foam and coke at high air compression temperatures.
Can this compressor be used for painting?
Yes, but only if a high-quality moisture-oil separator is installed. Oil mist from a refrigeration compressor will ruin the surface to be painted, so filtration at the outlet is required.
How often do you change the oil?
During intensive use (several hours daily), it is recommended to change the oil every 50-100 operating hours. With rare use - at least once a year, since the oil is hygroscopic and picks up moisture from the air.
Why does the machine knock out when starting?
The starting relay or capacitor may be faulty. Also, the cause may be low voltage in the network or too slow start due to residual pressure in the receiver (check the check valve).