Using an old refrigeration unit as a source of compressed air is a popular solution among home craftsmen, allowing them to save significant money on the purchase of new equipment. Many people wonder how to connect a compressor from a refrigerator in order to assemble a reliable compressor for a garage, workshop, or for airbrushing. Video instructions often show only the superficial part of the process, omitting important technical nuances that can lead to damage to the device or even injury if assembled incorrectly.
Unlike specialized air compressors, refrigeration units are initially designed to work with freon, not atmospheric air, which dictates its own pressure and resource limitations. However, with a competent approach and compliance with connection technology, such compressor can serve as a source of pressure for pneumatic tools, inflating tires or blowing out mechanisms for many years. It is important to understand that the process requires not only the mechanical connection of the tubes, but also the correct electrical switching of the starting device.
In this article we will analyze in detail all stages of the rework, from dismantling to the first start-up, paying special attention to safety and the selection of related materials. You will learn what types of oils cannot be mixed, how to correctly determine the purpose of the contacts and why it is prohibited to use R12 compressors with an open receiver for medical purposes due to the possible content of toxic decay products of old refrigerant.
Preparation of the workplace and necessary tools
Before starting assembly, it is necessary to prepare the space, since working with oil and metal elements can lead to contamination of the room. You'll need a workbench or stable table, good lighting, and access to a grounded electrical outlet for test runs. Do not forget that even when the unit is disconnected from the network, it may contain residual pressure, so the initial inspection should be carried out with caution.
To successfully complete the task of assembling a homemade installation, you will need a set of basic tools that are usually in the arsenal of any master. The lack of specialized equipment is not an obstacle, but the quality of the connections directly depends on the tools used.
- 🔧 Pliers and a set of wrenches for dismantling fasteners and tubes.
- ✂️ Nippers or side cutters for neat cutting of copper tubes.
- 🔌 Multimeter or tester for checking the motor windings and start relay.
- 🧤 Protective gloves and glasses to protect against splashes of oil and metal shavings.
Special attention should be paid to choosing a container for the receiver if you plan to create a full-fledged station rather than use the unit in the open. Old fire extinguishers or gas cylinders are often used as a receiver, but their preparation requires thorough cleaning of rust and testing for leaks under pressure exceeding the operating pressure. Tightness systems are a key parameter affecting the efficiency of the entire installation.
Removing the compressor and determining contacts
The first step is to carefully remove the compressor from the refrigerator. It is usually located at the lower rear of the unit and is mounted on four shock absorbing bushings. When sawing off copper tubes going to the condenser and evaporator, it is necessary to leave a length margin of at least 10 centimeters in order to be able to conveniently work with them on the table.
The most crucial moment is identifying the contacts on the starting relay, since an error in the connection can lead to burning of the windings or jamming of the piston group. There is often a diagram on the relay body, but if it is erased or missing, you will have to use a multimeter to check. At the outlet of the motor-compressor housing there are usually three contacts forming a triangle.
⚠️ Attention: Before carrying out any work on the electrical part, make sure that the power cord is disconnected from the outlet. Residual charge in capacitors (if they are present in the circuit) can be dangerous.
To determine the purpose of the contacts, measure the resistance between each pair of three terminals. The greatest resistance will be between the starting and working windings, the least - between the working winding and the common wire, and the average - between the starting winding and the common wire. The common wire (Common) is the reference point for connecting the phase.
Table of winding resistance
Usually the resistance of the working winding is 10-30 Ohms, and the starting winding is 30-60 Ohms, but the values may vary depending on the power of the motor and the manufacturer.
Connection diagram of the starting relay and capacitor
After identifying the contacts, it is necessary to correctly connect the starting relay, which can be inductive or posistor. Induction relays have a copper coil and a movable core; they are installed strictly in a certain position, indicated by an arrow on the body. PTC models are more modern and do not have moving mechanical parts inside, which makes them less sensitive to orientation in space, but more sensitive to overheating.
The connection is made according to the color marking of the wires or the terminals on the relay itself, where the letters C (or Com) indicate the common wire, R (or Run) is the working winding, and S (or Start) is the starting winding. If you are using a capacitor motor, the circuit may differ in the presence of an additional capacitor, which is constantly connected to the circuit or only at the time of startup.
It is important to ensure reliable contact at the junctions of the wires, using terminal blocks or high-quality soldering followed by heat shrink insulation. Poor contact will lead to heating, sparking and possible fire, since the currents when starting the engine can be significant.
☑️ Check before the first start
Organization of the lubrication and filtration system
Refrigeration compressors operate in a closed circuit where oil circulates together with refrigerant, therefore, when working in air, the lubrication system must be organized separately. There are two main approaches: maintaining internal lubrication (crankcase) or organizing external lubrication through a lubricator. The first option is simpler, but requires monitoring the oil level through an inspection window or dipstick, if provided by the design.
The inlet through which the compressor sucks in air must be equipped with an air filter. In the factory version, this function was often served by a muffler, but during conversion it is better to install a car fuel filter or a special air filter for compressors. This will prevent dust and abrasive particles from getting inside the cylinders, which is critical for maintaining the As for the type of oil, you can’t act at random. Old refrigerators used mineral oils, while new ones used synthetic oils (polyester device resource.
As for the type of oil, you can't act at random. Old refrigerators used mineral oils, new ones used synthetic (polyester) oils. POE or polyvinyl chloride PVE). It is strictly forbidden to mix them, as this will lead to the formation of an emulsion, sedimentation and rapid wear of the rubbing pairs. If you do not know what kind of oil is inside, it is better to drain the old one and fill in a new one that matches the type of seals.
Comparison of types of compressors for various tasks
The choice of a specific unit depends on the purposes for which you plan to use it. Not all compressors are the same: some models, especially inverter ones, are extremely difficult to start without a native control unit, while classic linear units are started by a simple relay. Understanding the differences will help you avoid wasting extra time.
Below is a table comparing the main characteristics of different types of compressors, which are most often found by craftsmen after recycling household appliances.
| Compressor type | Maximum pressure | Performance | Noise level | Starting difficulty |
|---|---|---|---|---|
| Linear (classic) | High (up to 25 atm) | Medium | High | Low (relay) |
| Inverter | Average | High | Low | High (requires block) |
| Piston open | Very high | High | Very high | Medium |
| Rotary (small) | Low | Low | Average | Average |
For airbrushing and small jobs, quiet models with low vibration levels are better suited, perhaps even with an additional soundproofing box. For garage needs, such as working with pneumatic tools, performance and the ability to quickly restore pressure in the receiver are more important, so here priority is given to classic piston units.
⚠️ Attention: Technical characteristics of compressors may vary depending on the manufacturer and year of manufacture. Always check the nameplate on a specific device before calculating loads.
Pressure settings and operational safety
After assembling the mechanical and electrical parts, it is necessary to test the system under load. The initial start-up should be carried out without connecting to the receiver in order to check the direction of rotation of the shaft (if this is important for a particular model) and the absence of extraneous knocks. A smooth hum of a running engine without rhythmic knocks or creaks is considered normal.
A mandatory safety element is the installation of a check valve between the compressor and the receiver. This element prevents the reverse flow of compressed air from the cylinder into the compressor after it stops, which protects the piston group from overload at the next start and prevents the receiver from discharging through the inlet filter.
It is also necessary to provide an emergency pressure relief system, for example, a safety valve set to a pressure exceeding the operating pressure by 10-15%. This will protect the structure from rupture in the event of a failure of the pressure switch or clogging of the system. Safety above all, since compressed air carries enormous energy.
Frequent errors and ways to eliminate them
In the process of self-assembly, craftsmen often encounter typical problems that can be avoided by knowing about them in advance. One of the most common mistakes is ignoring the heating of the case. Air-cooled compressors (and when operating in air they cool worse than in freon steam) can get very hot, requiring either forced airflow or interruptions in operation.
Another common problem is oil getting into the output air flow. This occurs if the oil level in the crankcase is too high or if the compressor operates in a mode not intended by design (for example, the frequency of switching cycles is too high). The solution is to install an oil separator at the outlet or adjust the oil level.
- ⚡ The compressor hums, but does not start - the start relay is faulty or the piston group is jammed.
- 🌡️ Strong heating of the housing - insufficient cooling or low oil level.
- 💨 Weak air pressure - wear of the piston rings or leaky connections.
- 🔊 Increased vibration - destruction of the rubber shock absorbers of the mount.
If you notice that the device consumes current significantly higher than the nominal current indicated on the tag, stop it immediately. This may indicate an interturn short circuit in the windings or mechanical jamming, which requires professional diagnostics or replacement of the unit.
Is it possible to use a compressor from an old refrigerator for airbrushing?
Yes, you can, but you will need to install an additional receiver to stabilize the air flow and a moisture separator, as pressure and steam pulsations oils can ruin the design. It is also advisable to install a reducer to accurately regulate the outlet pressure.
What kind of oil is best to pour into a homemade compressor?
It is best to use specialized compressor oils, but if this is not possible, you can use high-quality motor oil of the same viscosity that was drained from the unit. The main rule is not to mix mineral and synthetic oils.
Why does a compressor get very hot during operation?
Heating is a natural process of gas compression, but an excessive increase in temperature can be caused by a lack of lubrication, operation in a closed space without ventilation, or faulty valves causing air distillation.
Is it necessary to change the starting relay when making alterations?
If the original relay is working properly and matches the voltage of your network, there is no need to change it. However, if you plan to turn it on/off frequently (airbrush mode), it is better to replace it with a more reliable industrial relay or solid state.