Converting an old household refrigerator into a source of compressed air is a classic project for a home workshop, allowing you to save significant money on the purchase of professional equipment. Many craftsmen underestimate the potential of old refrigeration units, believing that their destiny is recycling, but it is inside these units that hides a powerful and durable piston mechanism. With proper modification, such compressor is capable of providing pressure to pneumatic tools, airbrushes and equipment for inflating tires.
The main idea is to remove the electric motor with a sealed housing and adapt it to work in an open circuit, where air is pumped into a special tank. Unlike factory models, a homemade design requires careful selection of control and safety system components. You will receive a device that is quieter than industrial analogs and does not require complex maintenance if all assembly stages are completed correctly.
Before proceeding with dismantling, you must clearly understand that the standard refrigerator cooling system and the pneumatic compressor system operate on different principles of medium circulation. In the refrigerator, freon moves in a closed cycle, and in the compressor, air must come from the atmosphere and go under pressure into the receiver. That is why a simple replacement of tubes is impossible without installing filters and valves, which will be discussed later.
Selection and preparation of the motor from the refrigerator
The first step is to find a suitable donor. The best choice would be compressors from Soviet-made refrigerators or modern models with a piston engine, as they are highly reliable and maintainable. It is important to avoid inverter models or units with linear compressors, since their electronics and design are not designed to operate in the mode of pumping air at high pressure into a standard pneumatic network.
When visually inspecting, pay attention to the integrity of the housing and the presence of all three pipes: two copper pipes for freon and one steel for refilling. For the modification we will need copper terminals. Before starting, be sure to check the operation of the electric motor by briefly applying power through the starting relay, which is usually attached to the side of the casing. If the shaft rotates and there is an air flow from the tubes, the unit is suitable for modernization.
⚠️ Attention: It is strictly forbidden to start the motor without a starting relay or with an incorrect winding connection diagram, as this will lead to instantaneous burnout of the winding or jamming of the piston group.
To successfully implement the project, you will need to assemble the following set of basic elements:
- 🔧 The compressor unit itself is assembled with a starting relay.
- ⚙️ Receiver (gas cylinder, fire extinguisher or resor from a truck).
- 📏 Pressure gauge for monitoring the pressure in the system.
- 🔩 Fittings, hoses and clamps for connecting units.
Particular attention should be paid to the condition of the oil inside the crankcase. When working with freon, special compressor oil was used, which can be hygroscopic. When converting to air, it is advisable to replace it with modern synthetic oil for compressors to prevent oxidation of internal parts and the formation of carbon deposits on valves.
Required tools and materials for assembly
The quality of the final product directly depends on how correctly the tools and components are selected. You don't need sophisticated industrial equipment, but a basic set of plumbing tools is a must. The key point is the preparation receiver of a container that will accumulate compressed air and stabilize the pressure.
Old fire extinguishers with a volume of 10-50 liters are most often used as a receiver, since they are initially designed for high pressure and have a reliable design. Gas cylinders from propane or resors from trucks are also suitable, but their preparation requires compliance with strict safety measures when removing remnants of the previous contents.
☑️ Checking readiness for assembly
For installation and connection of units you will need:
- 🛠️ Drill or screwdriver with a set of drills for metal.
- 🔨 Hammer, chisel and set of files.
- 🔥 Blowtorch or gas torch for soldering copper pipes.
- 📏 Tape measure, marker and square for marking.
Don't forget to purchase consumables: solder, flux for soldering copper, sealant resistant to oil and gasoline, as well as high-pressure hoses. All threaded connections must be sealed with FUM tape or similar materials to eliminate leaks that will reduce the efficiency compressor to zero.
Modification of the suction and discharge system
Standard design of the refrigeration unit The compressor assumes that the refrigerant circulates in a closed circuit, so the inlet and outlet are located close and do not have filters for atmospheric air. Our task is to change this scheme so that air is taken from the room, cleaned and supplied under pressure to the receiver. To do this, it is necessary to determine which of the copper pipes is suction and which is discharge.
The easiest way to do this is experimentally: when turned on for a short time, air will be blown out of one pipe (discharge), and sucked into the other (suction). The third, steel pipe, is usually sealed and serves for initial charging with freon - it can be used as a drain to drain old oil or plugged. An air filter must be installed on the suction pipe, for example, from a car or motorcycle, so that dust does not get inside the cylinders.
Why is the inlet filter important?
Foreign particles entering the cylinder act as an abrasive, quickly wearing out the piston rings and cylinder walls. In addition, dust mixes with oil, turning into an abrasive mess that can jam the valve mechanism. Using a filter increases the service life of a homemade compressor by 3-5 times.
A check valve must be mounted on the outlet pipe that goes to the receiver. This element is critical: it prevents compressed air from the receiver from returning back to the compressor after it stops. Without a check valve, the next time the engine is started, it will try to overcome the pressure in the tank, which will lead to overload and burning of the windings.
The connection of the compressor copper tubes to the adapters is carried out using soldering. It is important not to overheat the copper so as not to damage the internal insulation of the motor windings. Use soft solder and flux to ensure the seam is sealed. After soldering, the joints should be checked for leaks using a soap solution.
Installation of automation and safety systems
Safety is the main priority when working with pressure vessels. The basic control system should include a pressure switch (pressostat), which automatically turns off the motor when a preset limit is reached and turns it on when the pressure drops. This eliminates the need for the operator to constantly monitor the pressure gauge and manually control the power.
In addition, a safety valve must be installed on the receiver. If the pressure switch fails and does not turn off the motor, the pressure in the tank may exceed a critical value, which threatens to rupture the tank. The safety valve mechanically releases excess air, preventing an explosion.
| Component | Function | Recommended parameter |
|---|---|---|
| Pressure switch | Automatic on/off | 8-10 atm (switching off), 6-8 atm (switching on) |
| Safety valve | Emergency pressure release | Triggering at 12-15 atm |
| Pressure gauge | Visual control | Scale up to 16 or 25 atm |
| Check valve | Protection against reverse air flow | Compressor flow capacity |
| Pressostat | Electrical circuit switching | Motor current (usually up to 16A) |
| Drain valve | Condensate removal | Brass ball valve 1/2 inch |
The electrical circuit for connecting the pressure switch may seem complicated, but it is standard for all such devices. The relay opens the phase going to the engine when the upper pressure threshold is reached. It is important to select the correct cross-section of the wires so that they can withstand the starting currents of the electric motor, which can be several times higher than the rated ones.
Assembling and testing the finished device
After preparing all the components, we proceed to the final assembly. It is best to mount the compressor and receiver on a common frame or wooden platform to reduce vibration and noise during operation. Use vibration-isolating rubber pads under the legs of the unit, this will extend the life of the connections and make operation more comfortable.
Connect all the elements according to the diagram: Compressor -> Check valve -> Receiver -> Pressure switch -> Outlet valve. Make sure all threaded connections are tight and sealed. Before the first full start, conduct a leak test by pumping the system to 2-3 atmospheres and generously lubricating all joints with soapy water. The appearance of bubbles will indicate leak locations.
⚠️ Attention: Carry out the first start only in a well-ventilated area and wear safety glasses. Keep a safe distance from the receiver during the first minutes of operation in case of unexpected depressurization of welds or connections.
During the testing process, pay attention to the temperature of the compressor housing. When working with air compression, the heating will be stronger than when working with freon, but it should not be critical. If the body heats up to the point where it is impossible to touch it with your hand, it means that heat transfer is disrupted or the wrong oil has been selected.
Check the operation of the automation: bleed the air from the receiver through the outlet valve and wait until the motor turns on. Then close the outlet and watch the pressure gauge - when the set limit is reached, the engine should turn off. If everything works correctly, the assembly can be considered complete.
Operation and maintenance of a homemade compressor
A homemade compressor from refrigeration motor requires regular maintenance, especially in terms of changing the oil and removing condensate. During the process of compressing air from the atmosphere, moisture inevitably forms in the receiver, which mixes with oil and can cause corrosion of the internal walls of the tank. Therefore, after each use, it is necessary to open the lower drain valve and remove the accumulated liquid.
The oil in the compressor crankcase should be changed regularly, focusing on engine hours or degree of blackening. The use of high-quality synthetic oil significantly reduces operating noise and heating temperature. Also periodically check the condition of the air inlet filter: a clogged filter causes the motor to work with overload, reducing performance.
Do not forget that refrigeration compressors are not designed for continuous operation 24/7. They are designed for cyclic mode (works for 10 minutes, rests for 20). During intensive use with an airbrush or sandblaster, take breaks to allow the unit to cool, otherwise the thermal relay may cut off the power, or worse, an insulation breakdown will occur.
During storage compressor in an unheated garage in winter, make sure that no water remains inside the system. Freezing moisture can damage the valves or even burst the housing. It is best to store the unit in a dry room at above-zero temperatures.
What is the maximum pressure that can be obtained from such a compressor?
Refrigeration compressors are usually capable of creating pressure up to 10-15 atmospheres. However, the actual operating pressure is limited by the performance of the motor and the volume of the receiver. For most household tasks (painting, tire inflation), 6-8 atmospheres are sufficient. Exceeding the pressure requires a more powerful engine and a reinforced receiver.
Is it necessary to change the oil in the compressor during refurbishment?
Yes, it is advisable. Standard freon oil may be incompatible with atmospheric moisture and oxygen, which will lead to oxidation. It is better to drain the old one through a sealed fitting, flush the system with a special compound and fill with modern compressor oil with the viscosity recommended by the manufacturer of piston compressors.
Why does the compressor get very hot?
Heating is a natural process during gas compression. However, excessive heat may be caused by lack of cooling (fins on the housing), incorrect oil, clogged filter, or continuous operation. Make sure that there is air circulation around the motor and that it is not covered with casings during operation.
Can this compressor be used for pneumatic tools?
For powerful tools like impact wrenches or grinders, the performance of one refrigeration motor will not be enough. They consume hundreds of liters of air per minute, and the refrigerator produces about 40-60 liters. For an airbrush, inflating tires or blowing out, this is an excellent option.