Creating compressor from an old refrigerator is a classic project for the home workshop, which allows you to get a powerful and, importantly, quiet tool for painting, inflating tires or blowing out air tools. Unlike loud industrial counterparts, units based on refrigeration motors operate almost silently, which makes them ideal for working in a garage or even an apartment. However, simply replacing the tubes will not turn a household appliance into a full-fledged air blower.
The main difficulty lies in the correct preparation receiver and adaptation of the lubrication system. A standard refrigerator operates in a closed circuit with freon, and the compressor must pump atmospheric air, which contains moisture and dust. If you ignore the nuances of the alteration, the device will quickly fail or, in the worst case, become hazardous to health.
In this article we will analyze the step-by-step process of transforming a refrigeration unit into a reliable source of compressed air. You will learn how to choose a safe cylinder, correctly calculate the volume of the receiver and avoid common mistakes during assembly. Willingness to work with metal and compliance with safety precautions are prerequisites for the successful completion of the project.
Operation principle and selection of components
The heart of the future installation is piston compressor from the refrigerator. It is a sealed unit, inside of which there is an electric motor and a crank mechanism immersed in oil. The principle of operation is based on the reciprocating movement of a piston, which sucks in air through one valve and pushes it out under pressure through the other. Unlike open compressors, there is no direct access to the internals, which requires a special approach to maintenance.
To create an effective system, a container for accumulating compressed air is critically important. receiver . It is this that equalizes the pressure pulsations created by the piston and ensures a stable flow for the tool. Old propane or freon gas cylinders are most often used as a receiver. Their wall thickness and shape are ideal for working under pressure up to 10 atmospheres.
- 🔍 Power motor: Standard household units consume from 100 to 200 W, which is enough to create a pressure of 6-8 atmospheres.
- 🛢️ Refrigerant type: Preference should be given to models running on R12 or R134a freon, as they have a more reliable valve design.
- 🔇 Noise level: The sealed housing perfectly dampens vibrations, making the operation of the device comfortable for hearing.
When choosing a donor, pay attention to the condition of the case. There should be no through corrosion or dents on it, especially in the lower part where the oil intake system is located. It is also important to check the integrity of the starting relay and capacitor, since replacing them in sealed units requires opening the casing.
⚠️ Attention: It is strictly forbidden to use oxygen or acetylene cylinders for the receiver without special professional training and cleaning. Remaining gas or oils can cause an explosion upon contact with a spark or heating.
Preparation of a gas cylinder for the receiver
The most critical stage is preparing the container. Using a gas cylinder requires careful cleaning to remove condensation and odor. Even if the cylinder seems empty, heavy gas fractions always remain inside, which can ignite during welding or drilling. Therefore, the first step is always complete degassing.
The cleaning process begins with the removal of residual pressure. After opening the valve, the cylinder must be completely filled with water, displacing all the gas. Only after this can you begin machining. Water is drained only before welding so that the vapors do not form an explosive mixture with the air inside.
For ease of operation, additional elements must be welded to the cylinder. Typically, a tap for draining condensate is welded into the lower part, and pipes for connecting inlet and outlet air, as well as a pressure gauge and pressure switch, are welded into the upper part. All welding work is carried out in compliance with fire safety measures.
It is important to correctly calculate the thickness of the metal. For household compressors operating up to 10 atmospheres, a wall thickness of 3-4 mm is sufficient. If the metal is thinner, such a cylinder cannot be used - it may not withstand cyclic loads and burst.
Dismantling and preparing the compressor unit
Removing the compressor from the refrigerator requires care. The tubes leading to the block must not be cut with wire cutters, as metal shavings will certainly get inside the mechanism and jam the piston. They need to be sawed with a hacksaw or cut with special side cutters, leaving a margin of length for subsequent connection.
One of the main tasks is to determine the direction of the flows. Refrigeration compressors usually have three tubes: two on the housing and one sealed on the back side. Air is sucked in through one of the tubes on the body, and pumped through another (often thinner) one. The third, sealed, is used for refilling with freon and will not be used in our design.
To determine the inputs and outputs, you can apply a short-term current pulse. The tube from which air will be drawn when working for suction will be the entrance. However, there is a safer method: simply blow into the tubes with your mouth. The air will pass through the inlet air freely, but through the discharge air - with resistance or will not pass at all.
- ✂️ Cutting pipes: Leave a margin of 5-7 cm for convenient connection of hoses and installation of filters.
- 🧹 Cleaning: Before installation, blow the block with compressed air to remove any possible dust.
- 🔌 Electrical: Keep the starting relay and capacitor in the form in which they were connected, observing the orientation (top-bottom).
Pay special attention to the condition of the oil inside the unit. When working with freon, special synthetic or mineral oil is used, which is not hygroscopic. When working with air, it quickly oxidizes and loses its properties. Therefore replacing the oil with a regular motor oil (for example, 10W-40) is a mandatory procedure for the durability of a homemade compressor.
Connection diagram and system assembly
Assembling a pneumatic circuit requires compliance with the sequence of elements. Air from the atmosphere should not enter directly into the compressor without cleaning. An air filter must be installed on the inlet pipe to prevent abrasive dust from entering the cylinders. As a filter, you can use a zero-resistance car filter or a homemade cartridge.
The connection diagram is as follows: Atmosphere → Filter → Compressor → Check valve → Receiver → Pressure switch → Outlet tap. The check valve is critically important: it prevents compressed air from the receiver from going back into the compressor after it stops, preventing the shaft from turning in the opposite direction and discharging the tank.
☑️ Pneumatic system assembly checklist
To control the operation of the motor, it is used pressure switch (pressostat). It automatically turns on the compressor when the pressure in the receiver drops below the set minimum, and turns off when the maximum is reached. The electrical connection is carried out strictly according to the diagram supplied with the relay, with mandatory grounding of the housing.
All threaded connections must be sealed. For pneumatic systems, it is best to use an anaerobic sealant or FUM tape designed for high pressures. Ordinary tow can swell from condensation and break the seal.
Oil change and maintenance
As mentioned earlier, standard refrigeration oil is not suitable for working with air. It does not have sufficient antioxidant properties and quickly turns into a varnish substance that jams the mechanism. Replacement is made through a drilled and then plugged hole or through standard tubes until they are finally sealed.
The replacement process looks like this: old refrigerant and oil are removed by vacuuming or squeezing out. Then new oil is poured into the block (usually 250-350 ml, the exact volume depends on the model, see table below). The oil level should be strictly according to the mark on the inspection eye or be approximately 1/3 of the crankcase volume.
| Compressor model | Type of standard oil | Recommended oil | Volume (ml) |
|---|---|---|---|
| Atlant CK-10 | Mineral (Alkylbenzene) | Motor 10W-40 | 280-300 |
| Danfoss BD35F | Synthetic (POE) | Synthetics 5W-40 | 250-270 |
| LG MT | Mineral | Semi-synthetic 10W-30 | 300-320 |
| Embraco | Synthetic/Mineral | Motor 15W-40 | 290-310 |
The oil level should be checked regularly. If the compressor begins to “spit” oil into the pneumatic line, it means that the level is exceeded or the piston rings are worn out. In this case, it is recommended to install an oil separator at the outlet of the compressor, in front of the receiver.
Security setup and testing
The first launch is the most exciting moment. Before applying voltage, make sure that the outlet valve of the receiver is open so that the compressor does not pump into a closed volume immediately. Check that all elements are securely fastened to the frame. Vibration during operation can be significant, so the motor and cylinder must be rigidly secured through vibration supports.
A safety valve must be installed in the system. It will work if the pressure switch fails and does not turn off the motor when critical pressure is reached. Without this element, using a homemade compressor turns into a game with an explosion.
⚠️ Attention: Never leave a working homemade compressor unattended. Unlike factory models, there is no multi-stage protection system, and overheating or depressurization can occur suddenly.
After assembly, perform a leak test. Pump the receiver to 4-5 atmospheres and generously lubricate all joints, seams and joints with soapy water. The appearance of bubbles will indicate a leak that must be eliminated before commissioning.
What to do if the compressor gets hot?
Strong heating of the housing (up to 80-90 degrees) is normal for refrigeration compressors. However, if the temperature rises above 100 degrees or a burning smell appears, check the oil level and the operation of the cooling fan (if provided by the design). Also make sure that the break between operating cycles is sufficient for cooling.
Frequent problems and their solutions
During operation, typical malfunctions may occur. Most often, users experience a drop in performance or an inability to gain the required pressure. This may be caused by a dirty inlet filter or worn piston rings. Cleaning the filter solves the problem in 90% of cases.
Another common problem is frequent switching on and off (clocking). This indicates a large leak in the system or an incorrect delta setting of the pressure switch. If there are no leaks, the air flow may be too high relative to the volume of the receiver.
- 📉 Low pressure: Check the tightness of the valves (petals) inside the compressor head.
- 💧 Water in the air: Install an additional moisture separator or use a longer hose to cool the air in front of the tool.
- 🔊 Knock: The appearance of a knock indicates dilution of the oil or a foreign object entering the cylinder.
Regular maintenance, including draining condensate from the receiver (every 2-3 days of active operation), will prolong the life of your design for years. Rust inside the cylinder is the main enemy, so do not leave air in the receiver after work.
FAQ: Frequently asked questions
What is the maximum pressure that can be obtained from a refrigeration compressor?
Most household refrigeration compressors are designed for a condensation pressure of about 8-10 atmospheres. An attempt to increase the pressure above 12-15 atmospheres can lead to destruction of seals, gaskets or the housing itself. For most tasks (painting, tires) 6-8 atmospheres is quite enough.
Is it necessary to change the oil if the compressor runs rarely?
Yes, it is necessary. The chemical composition of refrigeration oil is not suitable for contact with air oxygen. Even with rare operation, it will oxidize, forming acid and carbon deposits, which will lead to corrosion of internal parts and jamming.
Can this compressor be used for airbrushing?
Only if a high-quality moisture-oil separator and pressure regulator are installed. Refrigeration compressors tend to drive oil into the pneumatic line, which is unacceptable for delicate work. Without thorough cleaning of the air at the outlet, the airbrush will “spit.”
Why does the compressor hum, but does not start?
Most likely, the thermal protection has tripped or the starting relay is faulty. The cause may also be piston jamming due to thickened oil or lack of lubrication. Let the motor cool and check the free rotation of the shaft (with the power off!).