An old refrigerator that has served its purpose often becomes bulky trash, which is a pity to throw away, but there is no place to store it. However, inside this household appliance hides a real technical gem compressor capable of creating pressure up to 10 atmospheres. Many DIYers have successfully converted this unit into a high-performance air compressor or vacuum pump for garage use. Such equipment is ideal for painting cars, inflating tires, working with pneumatic tools, or even for aerating large-volume aquariums.
Creating such a unit at home does not require deep engineering knowledge, but does require strict adherence to safety precautions and careful assembly. Hermetic compressors from Atlant-type refrigerators or Indesit have a unique feature: they are not afraid of moisture and are able to work in any conditions, unlike piston analogues. In this article we will analyze all the stages of turning an old motor into a useful tool that will last for many years.
The main advantage of this solution lies in the availability of components and their low cost if you use used equipment. You get a device that is quieter than industrial analogues and does not require complex maintenance. Oil system Inside the compressor, it provides lubrication of rubbing parts throughout its entire service life, which makes the design virtually maintenance-free in domestic conditions.
Before proceeding with dismantling, you need to make sure that it is in good working order the very heart of the future pump. If the refrigerator stops cooling due to a freon leak, the compressor is most likely working. However, if the problem was electrical or jamming of the piston group, then such a unit will not work. The check will take a little time, but will save you from useless work with non-working material.
Preparing tools and choosing a compressor
The first step is finding a suitable donor. The best candidates are considered to be compressors from Soviet-made refrigerators or modern models with cylindrical case. They are usually more powerful and repairable. It is important that there is no through corrosion on the case, and that the electrical part does not have signs of overheating or short circuit.
To successfully implement the project, you will need to collect a certain set of tools and materials. Without quality tools, the process can be delayed or lead to injury. Pay special attention to preparing the workplace, since the work will involve metal and electricity.
- 🛠️ A set of wrenches and screwdrivers for dismantling fasteners and connecting fittings.
- 🔌 Multimeter for testing the motor windings and checking the integrity of the circuit.
- 🧰 Copper tubes or high-pressure hoses for creating lines.
- 🔩 Fastening elements (bolts, nuts, washers) for fixing the unit to the frame.
Dismantling the compressor should be done carefully so as not to damage the copper pipes if you plan to use them. Bite off the tubes at a distance of 5-10 cm from the body, leaving the “tails” for later connection. If the pipes are rusted or broken off, they will have to be drilled out or replaced with new ones, which will require additional soldering skills.
⚠️ Attention: Before starting any work, be sure to disconnect the refrigerator from the power supply! Even when turned off, capacitors can retain a charge, and careless handling of wiring can be life-threatening.
It is also worth thinking in advance about the capacity for the receiver. This could be an old fire extinguisher, a gas cylinder, or a specially purchased receiver. The volume of the receiver directly affects the stability of pressure and the frequency of engine startup. The larger the volume, the less often the compressor will start, which will extend its life.
Checking performance and searching for pipes
After removing the compressor, you need to determine which of the three protruding copper tubes is the input and which is the output. Usually there is a marking on the case, but over the years of operation it can be erased or painted over. Identification of pipes This is a critical stage on which the correct assembly of the entire system depends.
The easiest way to determine the purpose of the tubes is to briefly apply voltage to the windings. When turned on, air will begin to come out of one pipe (output), and you can put your finger to the other and feel the suction (input). The third pipe is often sealed or used to charge the system with refrigerant; in our case, it is usually plugged or used as drainage.
| Pipe type | Function | Action during operation | Diameter (approximate) |
|---|---|---|---|
| Input | Air intake | Sucks in air | 6-8 mm |
| Output | Discharge | Blows out air under pressure | 6-8 mm |
| Filling | Service | Usually plugged | 3-5 mm |
Checking the electrical part is carried out with a multimeter in resistance measurement mode. It is necessary to ring the contacts between the starting relay and the motor windings. Lack of resistance (open) or zero resistance (short circuit) indicates a motor malfunction. Normally, the resistance of the starting winding is higher than the working winding.
If the compressor is equipped starting relay, it also needs to be inspected. Often it is this small plastic block that fails. There should be no cracks on it, and no melted contacts inside. The relay provides an initial jerk of the rotor, after which it turns off, so its serviceability is required for starting.
What to do if the compressor hums, but does not start?
If you hear a hum, but the shaft does not spin, the piston group may be jammed or faulty start relay. Try gently tapping the body with a wooden handle (not the copper pipes!). Sometimes this helps to move the pistons out of place. If it doesn’t help, check the relay or try to start the engine directly, bypassing the relay, by briefly applying current to the working winding.
Be careful: direct starting without a relay is only possible for a short time (2-3 seconds), otherwise the engine will burn out. If this does not help, the compressor is most likely mechanically faulty.
In some cases, adding special oil for compressors through the filling pipe helps if the old oil has thickened or evaporated.
Assembling the receiver and filtration system
The receiver acts as a buffer that accumulates compressed air and equalizing pressure pulsations, which are inevitable when operating a piston compressor. Without a receiver, the air flow will be jerky, which will make it impossible, for example, to perform high-quality painting or work with pneumatic tools. OU fire extinguishers or gas cylinders with a volume of 10-50 liters are ideal as a receiver.
Preparation of the cylinder requires thorough cleaning of the internal surface from rust and remnants of old contents. If moisture remains inside, it will enter the compressor and cause corrosion or emulsification of the oil. The cylinder must be washed with water with the addition of corrosion-resistant agents, then thoroughly dried and coated on the inside with an anti-corrosion compound, if possible.
- 💧 Moisture separator — mandatory for removing condensate from compressed air.
- 🛢️ Oil catcher —prevents oil mist from entering the pneumatic tools.
- 🌡️ Pressure gauge —for visual monitoring of the pressure in the system.
- ⚙️ Relay pressure —automates turning the compressor on and off.
It is important to equip the receiver with a safety valve. This element will relieve excess pressure if the pressure switch fails and does not turn off the motor. The valve response pressure should be slightly higher than the operating pressure of the system, but below the tensile strength of the cylinder. This is a critical safety elementthe presence of which protects against the explosion of the container.
The compressor is connected to the receiver through copper tubes or special hoses for high temperatures. It is advisable to install a check valve at the inlet to the receiver, which will prevent air from escaping back into the compressor after it stops. This will make it easier to restart the engine and protect it from overload.
Installation of electrical circuits and automation
The most difficult part of the project is connecting the electrics. The standard scheme includes connecting the engine to a 220V network via a starting relay and a pressure switch. The pressure switch (pressostat) opens the circuit when the specified upper limit of pressure is reached and closes it when it drops to the lower limit.
To connect, you will need to understand the markings of the contacts on the pressure switch. They are usually designated as (power line), (load, that is, compressor) and (ground). Inside the pressure switch there is a mechanical switch that is activated by air pressure from the receiver. Line (power line), Load (load, i.e. compressor) and Ground (grounding). Inside the pressure switch there is a mechanical switch that is activated by air pressure from the receiver.
Connection diagram:220V network --> Pressure switch (input)
Pressure switch (output) --> Compressor start relay
Start relay --> Motor windings
Don't forget about grounding! The compressor and receiver housing must be reliably grounded. Static electricity accumulated by air movement or breakdown of insulation can lead to electric shock. Use a copper wire with a cross-section of at least 1.5 mm² for grounding.
If you plan to use the compressor for delicate work, it makes sense to add a pressure regulator at the outlet of the receiver. This will allow you to reduce pressure for specific tasks without turning off the main unit. The regulator is installed after the air bleed valve and in front of the consumer hose.
⚠️ Attention: Carry out all work with electricity only with the power completely turned off! Errors in installing the pressure switch can lead to a short circuit or fire. If you are not confident in your skills as an electrician, contact a specialist.
☑️ Checking the electrics before the first start
First start-up and testing of the system
Before the first turn-on, check all connections again for leaks. You can use a soap solution: apply it to the pipe joints and threaded connections, then apply pressure. The appearance of bubbles will indicate a leak. Eliminate all defects by tightening the nuts or repacking the threads.
Start up in a well-ventilated area. The compressor may emit a specific smell of heating oil and paint in the first minutes of operation - this is normal. However, smoke or sparks are not permitted. Monitor the temperature of the case: it will heat up, but should not become red hot.
Check the operation of the automation. Pump the reservoir to maximum pressure and make sure the engine is turned off. Open the consumption tap, bleeding the air, and check whether the motor starts again when the pressure drops. The difference between the on and off pressure (hysteresis) is usually 2 atmospheres.
If the system is operating stably, you can proceed to testing with the tool. Connect the spray gun or blow-gun (blow gun) and evaluate the performance. If the pressure drops too quickly, the receiver may be too small or the compressor performance is insufficient for this tool.
Maintenance and typical problems
Although refrigeration compressors are considered maintenance-free, they require attention in constant operation. The main enemy is moisture that condenses in the receiver. Regularly (once a week with active use) open the drain valve at the bottom of the receiver to remove accumulated water.
Monitor the oil level if the design of your compressor allows you to check it (usually through an inspection window or dipstick, if one was provided). In hermetic compressors, the oil is rarely changed, but over long periods of operation (thousands of hours) it can lose its properties. Use only synthetic oils for refrigeration compressors, for example PAG or POE.
Typical problems that you may encounter:
- 📉 Falling performance - often caused by worn piston rings or clogged air inlet filter.
- 🔊 Increased noise —may indicate loosening of the mounting bolts or wear of the engine bearings.
- 🔥 Overheating —occurs when turned on too often (small receiver) or poor ventilation.
If the compressor starts spitting oil, check the oil level and the serviceability of the oil separator. Excess oil in the system is just as harmful as its lack, since it can clog a pneumatic tool.
Is it possible to use a compressor without a receiver?
Technically, you can start the compressor directly, without a receiver. However, the air flow will pulsate, making it impossible to use most air tools. In addition, the engine will turn on and off each time the trigger of the gun is pulled, which will quickly disable the start relay and the motor itself. A receiver is required for stable operation.
What is the maximum pressure such a pump can develop?
Standard household refrigeration compressors are designed for an operating pressure of about 6-10 atmospheres (bar). Some powerful models can briefly produce up to 15-20 atmospheres, but operation at the limit sharply reduces the resource. For most garage tasks (painting, inflating tires up to 3 atm, blowing), 6-8 atmospheres is quite enough.
Is it necessary to change the oil in the compressor?
In hermetic compressors, the oil is filled for the entire service life and does not require replacement under normal conditions. However, if you are rebuilding an old unit that has been running for 10-15 years, the oil may have oxidized or accumulated moisture. If it is possible to carefully drain the old and fill in the new (through a drilled and then welded hole or through pipes), this will extend the life of the pump. Use only specialized synthetic oils.
Why does the compressor get very hot?
Heating the housing to 60-80 degrees Celsius is normal for piston compressors. Heat is released when gas is compressed. However, if the housing becomes so hot that the wires burn or the paint melts on it, this is a sign of a malfunction: jamming, lack of lubrication, or improper operation of the valves. In this case, the unit must be turned off immediately.