Using decommissioned household appliances to create new useful devices is not just budget savings, but also a great way to get a tool with unique characteristics into the workshop. Refrigerator compressor is is an ideal candidate for such an upgrade because it is capable of generating high pressures, is relatively quiet and has a compact size. Unlike bulky piston analogues, such units are excellent for airbrushing, inflating tires, blowing electronics, or working with low-power pneumatic tools.
The main advantage of the conversion is the durability of the mechanism, which was originally designed for continuous operation in a closed circuit of the refrigeration cycle. However, in order to turn a household unit into a full-fledged one, it is necessary to correctly select additional components, such as a receiver and a control system. Incorrect assembly can not only lead to failure of the device, but also cause it, so the modernization process should be approached with a full understanding of the physical processes of gas compression. air blower, it is necessary to select the correct additional components, such as the receiver and control system. Incorrect assembly can not only lead to failure of the device, but also cause it, so the upgrade process should be approached with a full understanding of the physical processes of gas compression.
In this article we will analyze all the stages of transforming an old refrigeration unit into a powerful tool for the garage. You will learn how to calculate the required performance, choose a suitable tank for the receiver and correctly assemble a pneumatic circuit. A properly assembled unit will last for decades, providing a stable air flow for your needs.
Operating principle and advantages of a refrigeration compressor
Sealed units used in refrigerators are of the piston type, where the movement of the piston is carried out by a crank mechanism driven by an electric motor. The main feature of the design is the complete immersion of the motor and mechanical parts in oil, which provides excellent cooling and lubrication of rubbing parts. It is thanks to this that refrigeration compressor is able to work for hours without overheating, if the operating conditions are met.
When remodeling, it is important to understand that such devices are not designed for directly drawing in large volumes of atmospheric air, they are optimized for freon circulation. However, their design allows for efficient compression of air, although the efficiency may differ slightly from specialized air pumps. The key success factor is the correct organization of suction and discharge, as well as the removal of heat generated during compression.
- 🔧 Low noise level during operation, which allows the device to be used even in a residential area or a small workshop.
- 💰 High availability and low cost of the main unit, which can often be obtained for free when disposing of old equipment.
- ⚙️ The simplicity of the design of the electric motor, which does not require complex maintenance or frequent replacement of brushes.
It is worth noting that the performance of such units is usually lower than that of industrial analogues, but for everyday tasks it is more than enough. The outlet pressure can reach significant values, but the actual volume of pumped air is limited by the power of the motor. The maximum operating pressure of hermetic compressors often exceeds 10 atmospheres, but for the safe operation of home-made systems it is usually limited to 6-8 bar.
⚠️ Attention: The compressor housing is filled with oil, which, when working with air, can enter the pneumatic system. Be sure to install an oil separator if you plan to use the tool for painting or airbrushing, otherwise the oil suspension will ruin the coating.
The electric motor inside the casing is usually asynchronous and is started through a starting relay. When remaking, it is important to maintain the standard connection diagram or replace it with a more reliable one if the original relay fails. Understanding the electrical part is necessary to safely connect the device to a 220V network.
The necessary materials and tools for assembly
A motor alone is not enough to create a high-quality device. You will need to assemble a whole set of components, each of which performs a critical function in the overall system. Receiver (the air storage tank) is the heart of the system, smoothing out pressure pulsations and allowing the compressor to operate in normal mode.
Old gas cylinders, fire extinguishers or specially welded containers are most often used as a receiver. thick-walled pipes. It is important that the material of the tank can withstand pressure with a reserve, so the use of plastic canisters or thin-walled containers is strictly prohibited. You will also need a filtration system, pressure gauges and shut-off valves.
Below is a table of the main components required for assembly:
| Component | Purpose | Minimum requirements |
|---|---|---|
| Receiver | Air accumulation | Volume from 10 liters, pressure 15+ atm |
| Manometer | Pressure control | Scale up to 10-12 bar |
| Pressure switch | Automatic switching on | Setting 4-6 bar |
| Oil separator | Air purification | Fine filter |
As for tools, you will definitely need a set of wrenches, a drill or screwdriver, a hacksaw and, possibly, a welding machine if you decide to make a frame or modify the receiver. To seal the connections, prepare FUM tape or anaerobic sealant that is resistant to oil and air.
☑️ Shopping and search list
Preparation and dismantling of the compressor unit
The first stage of work is removing the compressor from the old refrigerator. To do this, you need to carefully saw off or bite off with pliers the copper tubes that fit the body, leaving their “tails” 5-10 cm long. These remains of the tubes will be needed later to connect hoses and determine the direction of flow.
After removal, the unit should be cleaned of dust, dirt and rust. Pay special attention to the electrical part: check the integrity of the wire insulation and the condition of the starting relay. If the relay has traces of carbon deposits or melting, it is better to replace it with a new one corresponding to the engine power in order to avoid problems with starting.
The most important point is to determine the input and output. Refrigeration compressor tubes have different diameters: the thinner tube is usually the suction tube, and the thicker tube or one that comes from the condenser is the discharge tube. To avoid mistakes, you can briefly plug in the device and blow your finger into each tube - the air will come out of the discharge tube with noticeable pressure.
⚠️ Attention: Never start the compressor with open tubes without preparing the work site. A jet of old oil can fly out of the pressure pipe under pressure and stain everything around it. Place a hose or plug on the outlet pipe in advance.
If the compressor has been sitting for a long time, the oil inside could oxidize or mix with moisture. In an ideal scenario, it is recommended to replace it with fresh compressor oil, although many technicians successfully operate units with old lubricant, simply changing the filters more often. To change the oil, the bottom of the casing is cut off, the old oil is drained, and new oil is poured up to the mark.
What kind of oil should be poured into the compressor?
For lubrication, it is best to use special synthetic or semi-synthetic compressor oils, for example, Fuchs Reniso or analogues. It is not recommended to use regular motor oil as it may foam and impair the performance of the device. The oil volume is usually 300-400 ml, but it is better to check the exact level using a sight glass or dipstick, if provided by the design.
Manufacture and preparation of the receiver
The receiver functions as a buffer, accumulating compressed air and allowing the compressor to turn off when the pressure has reached its maximum. Without this element, the engine would turn on and off too often, which would quickly damage it. The best material for a homemade receiver is steel, which can withstand high pressure without the risk of rupture.
The best option for a home handyman is to use fire extinguishers with a capacity of 10-50 liters. They already have the required wall thickness, are tested for strength and are often equipped with convenient fastenings. Before use, the fire extinguisher must be emptied of its contents, thoroughly rinsed inside with water and detergent and dried to prevent corrosion from residual powder or moisture.
In the upper part of the receiver, holes must be drilled and welded (or screwed onto the thread with sealant) fittings for connecting the compressor, air outlet to the consumer, pressure gauge and safety valve. The location of the holes should ensure ease of installation and maintenance. If you use a gas cylinder, make sure that it is completely emptied of gas and steamed to eliminate the risk of explosion during welding.
A drain valve for condensate must be installed at the lowest point of the receiver. In the process of air compression, moisture is released from the atmosphere, which accumulates in the tank. If it is not drained, water will enter the air tool and cause corrosion of the internal parts of the system. Regular drainage of condensate prolongs the life of the entire pneumatic network.
The volume of the receiver directly affects the frequency at which the compressor is turned on. For small tasks, such as inflating tires or working with an airbrush, a tank of 10-20 liters is sufficient. If you plan to use grinders or pneumatic impact wrenches, the volume should be increased to 50 liters or more, or two compressors should be used in parallel.
Assembling a pneumatic system and automation
Assembling a pneumatic circuit requires consistency and tightness. Air from the compressor must first pass through a pre-filter or oil separator before entering the receiver. This will protect the tank from oil contamination. At the outlet of the receiver, an air preparation system is installed: a filter-moisture separator, a reducer (for adjusting the pressure under the tool) and a lubricator (if the tool requires air lubrication).
The key element of automation is pressostat (pressure switch). This device monitors the pressure in the receiver and automatically turns on the compressor when it drops to the lower limit and turns off when it reaches the upper limit. The pressure switch is connected to the break in the electrical power supply circuit of the engine and to the pneumatic line of the receiver.
- 🔌 Connect the phase and zero from the network to the input terminals of the relay.
- ⚡ Connect the output terminals of the relay to the starting compressor device.
- 🔩 Be sure to ground the compressor housing and receiver for safety.
The pressure switch is adjusted using the adjusting screws under the cover. Typically the factory settings are 4 atmospheres for on and 6 atmospheres for off. It is not recommended to increase the upper threshold above 8-9 atmospheres for homemade systems, as this creates an excessive load on the components.
⚠️ Attention: Installation of a safety valve is mandatory! It should operate at a pressure exceeding the maximum allowable for the receiver (for example, at 10 atm, if the tank holds 12 atm). This is the only protection against a tank explosion in the event of a pressure switch failure.
To connect all elements, use copper tubes or special high-pressure hoses, securing them with clamps. Rubber hoses from drippers or irrigation are not suitable - they will burst under pressure. Seal all threaded connections with FUM tape or thread to avoid air whistling and loss of performance.
Testing and first start-up of the device
Before a full launch, it is necessary to conduct a visual inspection of all connections and electrical parts. Make sure that the drain valve on the receiver is open so that the compressor does not immediately pump air into a closed system, and also check the oil level. Plug in the device and listen to the operation: there should be no extraneous knocks, vibrations or sparking.
Close the drain valve and observe the pressure gauge readings. The compressor must build up pressure to the limit set on the relay and automatically turn off. In this case, the characteristic sound of the engine should stop. If the engine does not stall, but continues to hum, bleeding air through the valve, it means that the pressure switch is not adjusted or is faulty.
Check the system for leaks using a soap solution. Apply foam to all joints of pipes, fittings and joints. The appearance of bubbles will indicate a leak that must be eliminated by tightening the threads or replacing the seal. Even a small leak will eventually lead to the motor constantly turning on and overheating.
After a successful pressure test, let the device run in idle mode (without connecting a tool) for about 15-20 minutes. Check the temperature of the compressor housing: it may get hot, but should not be hot. If the temperature rises uncontrollably, the cooling system may be broken or the oil is low.
The finished compressor can be mounted on a frame with wheels for mobility or mounted on a wall in a workshop. Don’t forget to equip the structure with vibration mounts (rubber pads) to reduce noise and vibration during operation. Now your homemade unit is ready for useful work.
Is it possible to use a compressor without a receiver?
Theoretically, you can start the compressor directly, without a receiver, but doing this is highly not recommended. Without a buffer tank, the engine will turn on every time you open the air supply valve, which will lead to rapid wear of the starting equipment and overheating of the windings. In addition, the air flow will pulsate, which will make it impossible to work with a paint sprayer or other sensitive tool.
What is the maximum pressure that a refrigerator can develop?
Hermetic compressors from household refrigerators are structurally capable of developing pressure up to 15-25 atmospheres and even higher, but their actual productivity (liters per minute) at such pressure drops almost to zero. For safe and efficient work in conjunction with pneumatic tools, the range of 6-8 atmospheres is considered optimal.
Why does the compressor get very hot?
Heating of the housing to 60-80 degrees Celsius is normal for sealed units, since cooling occurs due to airflow and heat transfer through the walls. However, if the temperature exceeds 90-100 degrees, this may indicate a lack of oil, operation in constant pressure mode (leaks), a faulty start relay, or insufficient ventilation around the device.
How often should the oil be changed?
Unlike open compressors, in sealed refrigeration units the oil is rarely changed, usually only during major repairs or if it is significant lost its properties (turned black, became thick). Under normal operation and the use of an oil separator filter at the outlet, replacement may not be required for years. However, the oil level should be checked annually.