Converting an old refrigerator into a source of compressed air is a classic project for the home workshop, allowing you to get a powerful and, importantly, silent tool. Compressor from a refrigerator motor ideal for airbrushing, inflating tires and working with pneumatic tools that do not require huge air consumption. Unlike bulky industrial analogues, such a unit takes up minimal space and consumes significantly less electricity.
The main value of the modification lies in the durability and reliability of refrigeration units, which were originally designed for round-the-clock operation in a closed circuit. However, in order to turn a sealed unit into an effective air blower, it is necessary to select the right attachments and follow the installation technology. In this article we will analyze in detail the process of creating a homemade compressor, avoiding common mistakes of beginners.
Selection and diagnosis of the original motor
The first step will be to find a suitable donor. For our purposes, motors from Soviet-made domestic refrigerators, such as ZiL or Saratovare best suited, since they are often equipped with copper tubes, which are easier to solder than modern aluminum. However, modern units running on R134a or R600a freon are quite suitable if they are in good working order. The main requirement is that the motor must start, run smoothly and have no mechanical damage to the housing.
The performance test is carried out by briefly plugging it into the network. Hermetic compressor when starting, it emits a characteristic hum, and an air flow begins to flow from the outlet tube. It is important to make sure that the motor does not blow out automatic fuses and does not overheat after 10-15 minutes of operation. If the unit hums but does not start, the start relay may be faulty, which can also be used in a new design.
⚠️ Attention: Never leave a running motor unattended during the early stages of testing. If there is depressurization or a short circuit, the oil or electrical wiring may ignite.
When choosing, pay attention to the type of refrigerant for which the unit is designed. Although we will be pumping air, the valve design may vary. Motors that worked on Freone-12often have higher performance, but finding them is now difficult. For garage needs, a standard single-piston unit with a power of 100–200 W is quite sufficient.
Necessary materials and tools
Assembling a high-quality compressor requires careful preparation. You will need not only the motor itself, but also a container for storing compressed air, called a receiver. Old fire extinguishers with a volume of 10–20 liters, freon gas cylinders, or even reinforced battery housings are often used as a receiver. The key element is control system, which includes a pressure switch and a pressure gauge for monitoring parameters.
To connect all components, you will need a set of fittings, hoses and adapters. It is better to replace the tubes coming out of the motor with copper or brass ones, since the standard ones may be too thin or fragile after dismantling. It is also necessary to purchase compressor oil if you plan to change it during the conversion process, although many models operate on what is poured inside.
Below is a table of the main components required for assembly:
| Component | Purpose | Approximate cost |
|---|---|---|
| Pressure switch | Automatic on/off | Average |
| Pressure gauge | System pressure control | Low |
| Receiver | Air accumulation and stabilization | Depends on the capacity |
| Check valve | Protecting the motor from backflow | Low |
Don't forget about tools: you will need wrenches, a drill, a set of drills, a soldering iron or a gas torch for working with tubes, as well as sealant or FUM tape for sealing threaded connections. High-quality preparation of the tools will speed up the process and ensure the tightness of the system.
Dismantling and preparing the compressor
The process of removing the motor begins with carefully sawing off the copper tubes. It is important to be carefulto prevent sawdust or metal shavings from getting inside the housing, which can instantly kill the valve mechanism. It is recommended to use a pipe cutter or carefully work with a hacksaw, after bending the tubes to the sides. After disconnecting the tubes, the motor is removed from the frame of the refrigerator along with the start relay.
The next step is to determine the input and output. There are usually three terminals on the compressor housing: two for connecting to the network and one for grounding. There are also several tubes: one suction (input) and one or two discharge (output). To avoid confusion, just briefly turn on the motor and place your finger at the ends of the tubes - where it blows, there is an exit; where it sucks, there is an inlet.
After determining the sides, you need to clean the body from dirt and rust. If the engine has been sitting in a damp garage for a long time, it should be dried. Some masters recommend rinsing the insides with a special solvent through the inlet tube to remove decay products of old oil, but this requires subsequent thorough drying.
⚠️ Attention: It is strictly forbidden to open the sealed motor casing with a grinder or a hacksaw. This will disrupt the alignment of the parts and make the unit unsuitable for further use.
Manufacture and preparation of the receiver
The receiver is the heart of your pneumatic system, responsible for storing air and dampening flow pulsations. The most affordable and safest option is to use a metal fire extinguisher. Before use, make sure that the cylinder is free of corrosion and mechanical damage. The bottom and neck are the most vulnerable places that require careful inspection.
The preparation process includes inserting fittings. A tee or manifold is installed in the upper part of the cylinder (where the neck of the fire extinguisher was) into which a pressure gauge, pressure switch and outlet valve fit. To insert into the wall of the cylinder (if required), it is necessary to use metal drills and taps for cutting threads. All connections must be made using heat-resistant sealant.
Condensation may form inside the receiver, so a drain valve must be provided at the bottom point of the cylinder. This will allow you to regularly remove accumulated water, preventing corrosion of the metal from the inside. Draining condensate - a procedure that cannot be ignored, otherwise rust will quickly disable the container.
Why can’t you use plastic cans?
Plastic under pressure it can burst with flying fragments. In addition, many plastics cannot withstand the temperature of compressed air and oil, which leads to deformation and destruction of the container.
Assembling a pneumatic system
Assembling the system begins with installing a check valve between the compressor and the receiver. This element prevents the reverse flow of air from the cylinder into the motor after it is stopped, which protects the piston group from overload the next time it is started. Without a check valve, the pressure switch may not work correctly, or air will flow back through the inlet tube.
Next, a pressure switch (pressostat) is installed. It connects to the receiver and the electrical circuit of the motor. The relay's task is to open the circuit when a predetermined maximum pressure is reached and close it when it drops to the minimum threshold. These thresholds are adjusted using the adjusting screws under the relay cover. Standard values for homemade systems: on at 2 atm, off at 6–8 atm.
To connect all elements, use copper tubes or special high-pressure hoses. Rubber hoses from water systems will not work - they may not withstand the pressure and burst. All threaded connections are sealed with FUM tape or thread. After assembling the entire “air” part, but before connecting the electrics, it is recommended to carry out an initial purge.
☑️ Checking the assembly
Pay special attention to vibration isolation. The motor vibrates during operation, and if it is rigidly mounted on the receiver, the vibration will be transmitted to the cylinder, creating additional noise and the risk of damage to the connections. Use rubber gaskets or short pieces of oil-resistant hose between the motor output and the receiver pipes.
Electrical circuit and starting
Connecting the electrical part requires basic knowledge in electrical engineering. The refrigerator motor is usually connected through a start relay, which is already installed on its body. The circuit is simple: phase and zero go to the relay input, and from it to the motor windings. The pressure switch is connected to the phase wire break, providing automatic control.
For system safety, be sure to install a circuit breaker at the power input. It will protect the wiring from short circuits and overloads. The cross-section of the wire must correspond to the power of the motor; For most refrigeration units, a wire with a cross-section of 1.5 mm² is sufficient. Do not forget about grounding: the motor housing and the receiver must be grounded.
Connection diagram:
220V network -> Automatic -> Pressure switch -> Motor start relay -> Motor
Perform the first start in a well-ventilated area. Turn on the machine and observe the pressure gauge readings. The motor must build up pressure to the set threshold and turn off. If it does not turn off, check the settings of the pressure switch or the tightness of the system (there may be a leak and the compressor cannot pump up the required pressure).
Maintenance and safety measures
A homemade compressor, like any technical device, requires regular maintenance. The main enemy of the system is moisture, which condenses when air is compressed. Open the drain valve at the bottom of the receiver regularly, especially after intensive work. Ignoring this rule will lead to corrosion of the cylinder from the inside.
Monitor the level and condition of the oil. Although refrigeration compressors are considered maintenance-free, when used intensively as an air blower, the oil can burn or oxidize. If you notice a decrease in performance or the appearance of oil mist in the exhaust air, you may need to change the oil through a carefully drilled and then welded hole (which is done by experienced craftsmen) or replace the entire unit.
⚠️ Attention: The pressure in the system should not exceed the permissible standards for your receiver. Using an overly powerful motor with a small cylinder without the correct pressure switch can lead to an explosion.
When storing the compressor, bleed off any residual pressure in the receiver. Long-term storage under pressure weakens the metal and deforms the seals. It is also recommended to periodically check the tightness of all bolted connections, as vibration can weaken them.
Frequently asked questions (FAQ)
Is it possible to use a compressor from a refrigerator for a spray gun?
Yes, you can, but with restrictions. The spray gun needs a stable air flow. The refrigeration motor has a low capacity (liters per minute), so it will only work with small volume spray guns (HVLP low consumption) and as long as you pause to build up pressure. Its power is not enough for professional car painting.
What oil is best to fill in such a compressor?
A special refrigeration oil is already filled inside. If replacement is required, use synthetic oils compatible with freon (for example, polyester) or special compressor oils. Regular motor oil can coke and damage the valves.
Why does the compressor get very hot?
Heating to 60–80 degrees Celsius is the norm for such engines. They are designed to work with hot gas. However, if the temperature exceeds 90–100 degrees or a burning smell appears, check the ventilation, oil level and the absence of air leaks causing the motor to work without interruption.
Is it necessary to change the oil in a new compressor?
In a new or serviceable used motor, there is no need to change the oil unnecessarily. The sealed system is designed to last a lifetime. Opening to change the oil often leads to moisture and dirt getting in, which is more harmful than old oil.