Using a compressor from a household refrigerator is a popular solution for home workshops, garages and small industrial needs. This unit is capable of creating excess pressure sufficient to operate pneumatic tools, paint guns, airbrushes, and even to inflate tires. However, unlike factory compressors, a refrigeration engine requires proper preparation and adherence to strict safety rules before the first start.
The main feature of such devices is that they were originally created to operate in a closed circuit of the refrigeration system, and not to pump air into the atmosphere. Therefore, simply applying voltage to the contacts does not guarantee successful operation and may result in damage or injury. In this article we will analyze in detail the technical nuances necessary for safe and efficient work with this equipment.
Before starting assembly, you need to make sure that the engine itself is in good working order. Quite working units that are simply disconnected from the system often end up in landfills or collection points. The inspection begins with a visual inspection of the housing to ensure there are no dents, signs of rust and, critically, the integrity of the copper tubes. If the tubes are pinched or cut, air and moisture could get inside, which will require a complex evacuation procedure.
Preparing equipment and checking serviceability
The first step is to determine the type of compressor and its current condition. Most household models are sealed piston units, inside of which there is oil to lubricate the rubbing parts. Sealed case does not allow you to just look inside, so primary diagnostics are carried out by external methods. You need to find three terminals on the case where the start relay was connected.
To check the functionality, you will need a power source, wires and, preferably, a multimeter. Do not connect the unit directly to the outlet without first checking the circuit, as incorrect switching of the windings can lead to a short circuit or hum without starting the rotor. Carefully inspect the contact group: it should be clean, without traces of carbon deposits or oxidation.
⚠️ Attention: Never run the compressor with open pipes in a closed room without ventilation. The exhaust air contains oil mist and freon vapor (if it remains inside), which is harmful to health. Work only in a well-ventilated garage or outside.
If the device visually looks intact, you can conduct a test run. To do this, you need to temporarily connect the starting relay, since it is this that provides the necessary phase shift to start the engine. Without this element, the motor will only hum, trying to move the piston from a dead point, which will quickly lead to burnout of the windings.
Connection diagram and operation of the starting relay
The key element in the starting circuit is start relay. This device automatically supplies current to the starting winding only at the moment of start, and then turns it off, leaving only the main winding to work. The relay housing usually has arrows indicating up and down, which is critical for proper installation, since there may be a moving core inside that is dependent on gravity.
Connection is made to three contacts on the compressor housing. They are usually arranged in a triangle. In order not to get confused where the phase, zero and starting winding are, you should use a multimeter in resistance measurement mode. The resistance between the main and starting windings will be the sum of their individual resistances. The connection diagram is standard for most models Atlant, Don or Indesit.
The connection process is as follows:
- 🔌 Determine the contacts: find the pair with the highest resistance - these are the ends of the starting and working windings, the third contact will be common.
- 🔌 Install the relay: put the starting relay on the contacts strictly in accordance with the markings (often marked with the letters S, R, C or numbers).
- 🔌 Connect the power: to the common contact and the working contact windings, connect the wires from the plug with mandatory grounding.
After assembling the circuit, plug the device into the network. If you hear a confident hum and feel a flow of air from the outlet pipe, the launch was successful. If there is a humming sound but no rotation, turn off the power immediately. This may indicate a jammed mechanism or a faulty relay. In some cases, replacing the relay with a similar one from the same refrigerator helps.
What to do if the relay clicks, but there is no start?
If the relay constantly clicks, trying to start the engine, but the shaft does not rotate, the piston may be stuck or the oil has dried out. In rare cases, gently tapping the body with a wooden mallet in a horizontal position helps, but this is a temporary measure. Often disassembly and troubleshooting is required, which is difficult at home. Also, the cause may be a break in the starting winding.
Modernization: creating a receiver and filtration
Using a compressor simply with a tube sticking out is ineffective and dangerous. The air flow pulsates, which makes it impossible to work with a spray gun or thin pneumatics. To smooth out pulsations and create a supply of compressed air, it is necessary receiver. Old gas cylinders, fire extinguishers or specially prepared containers are often used as a reservoir.
The most important stage of modernization is the filtration system. At the outlet of a refrigeration compressor, the air always contains oil particles that are thrown out along with the flow from the crankcase. If this air is fed into the spray gun, the paint will be damaged. Therefore, an oil separator must be installed at the outlet, which can be made independently from a transparent flask with filler.
The piping diagram of the compressor group should include:
- 🛡️ Inlet filter: installed on the suction pipe to clean the incoming air from dust, preventing abrasive wear of the cylinders.
- 🛡️ Check valve: prevents air from leaving the receiver back into the compressor after it stops, protecting the mechanism from water hammer.
- 🛡️ Pressure switch (pressostat): automatically turns off the engine when the set pressure in the receiver is reached and turns it on when fall.
☑️ Assembling the compressor unit
Technical characteristics and limitations
Refrigeration compressors are not designed to create high pressure, like professional piston models. Their working area is usually in the range of 6-8 atmospheres, although for a short time they can produce more. However, prolonged operation at extreme conditions leads to overheating and destruction of the seals. The maximum safe pressure for most household refrigeration compressors is 10-12 atmospheres; exceeding this threshold is strictly not recommended.
The performance of such units is also limited. They are designed to work in a cyclic mode: 15 minutes of work, 45 minutes of rest (or a similar cycle, depending on the model). Constant work 24/7 without breaks will lead to rapid wear and tear. The table below shows approximate characteristics of popular types of compressors.
| Compressor type | Power (W) | Performance (l/min) | Max. pressure (atm) |
|---|---|---|---|
| Low temperature (R12, R134a) | 100-150 | 30-50 | 8-10 |
| Medium temperature (R404a) | 150-250 | 50-80 | 10-12 |
| Inverter (modern) | 80-120 | 40-60 | Depends on frequencies |
Please note that inverter models require complex electronics to control the rotation speed and cannot operate from a regular 220V network without a special converter. For homemade compressors, good old linear units with a starting relay are better suited.
Safety measures during operation
Working with high pressure and electricity requires extreme caution. The receiver, being a pressure vessel, is potentially dangerous. If you are using an old fire extinguisher or gas cylinder, make sure it has been leak tested and is not corroded on the inside. Internal rust can cause a spark or cause the container to rupture.
The electrical part also requires attention. Compressors are often installed in damp garages or basements. Grounding enclosures are a requirement. The use of sockets without a grounding circuit is unacceptable, since if the insulation breaks down, a dangerous potential of 220V will appear on the housing.
⚠️ Attention: The temperature of the housing of a working compressor can reach 90°C and higher. Do not touch metal parts during operation and immediately after switching off. Make sure that the device is installed on a non-flammable surface and there is space around it for cooling.
Also, pay attention to the noise level. Refrigeration compressors are considered quiet only in the context of operating a kitchen refrigerator. In a small workshop, their humming can be tiresome, so consider making a noise-absorbing box with ventilation.
Typical faults and their elimination
During the operation of a home-made installation, various problems may arise. Most often, users are faced with the fact that the compressor hums, but does not pump, or often turns on and off. The first situation often indicates a loss of performance of the piston group or air leakage through the valves.
If the engine constantly overheats and is turned off by the thermal relay, check the voltage in the network. A voltage drop below 190V leads to the fact that the engine does not develop the required power, the current increases, and the thermal protection breaks the circuit. Also, the cause may be contamination of the condenser (black grille at the back), which is often absent in air compressors or replaced with passive cooling.
Frequent activation of the pressure switch may indicate:
- 🔧 Leakage air: check all connections with a soapy solution, bubbles will indicate where the gas is escaping.
- 🔧 Check valve malfunctions: air goes back to the compressor head.
- 🔧 Small volume of the receiver: for high air consumption, the capacity is not enough, and the pressure drops too quickly.
Frequently asked questions (FAQ)
Is it possible to use automobile oil to lubricate a refrigeration compressor?
No, you cannot. Refrigeration compressors use a special synthetic oil (mineral or polyester) that is mixed with the refrigerant and circulated through the system. Conventional motor oil can foam, coke upon contact with freon residues, or fail to provide the required viscosity, which will lead to scuffing of the piston group.
What volume of the receiver is optimal for painting?
For high-quality painting without ripples and pulsation, a receiver with a volume of at least 50 is recommended liters Smaller volumes (10-20 liters) are suitable only for inflating tires or blowing parts, but they will not be enough for a spray gun, even taking into account the low performance of the refrigeration compressor.
Why does the compressor get very hot?
Heating to 70-90 degrees is the normal operating mode for many piston units. However, if the temperature exceeds 100 degrees, the device goes into protection. Reasons: poor ventilation, too high frequency of switching on, low voltage in the network or wear of parts that creates increased friction.
Is it necessary to change the oil in a compressor from a refrigerator?
In sealed factory versions, the oil is designed for its entire service life and does not require replacement. However, in homemade installations where the compressor operates under more severe conditions (air intake from the atmosphere, presence of moisture), the oil can oxidize. If it is possible to drain the old oil and fill in new oil (through a drilled and then welded hole or through pipes before assembly), this will extend the service life.
Is it possible to connect the compressor directly without a relay?
Theoretically, you can start it by forcibly closing the contacts of the starting winding manually for 1-2 seconds, but operate it like this is strictly prohibited. Without automatic shutdown of the starting winding, it will burn out in a matter of minutes. A relay is a mandatory design element.