Using an old compressor from a failed refrigerator is a great way to get a powerful and relatively quiet source of compressed air for garage needs. Units from household appliances often have excess a resource that allows them to work for years as the basis for a homemade compressor. Unlike bulky and noisy industrial-type piston models, refrigeration motors operate much quieter and take up minimal space.
However, before you begin assembly, you need to make sure that the engine itself is in good working order and understand the principle of its operation. Sealed housing hides inside not only an electric motor, but also and a lubrication system, which is critical to the longevity of the device. Incorrect connection or violation of operating conditions can lead to rapid failure of even a seemingly serviceable unit, so theoretical preparation here is no less important than the availability of tools.
In this article we will analyze in detail the process of resuscitating old equipment, wiring diagrams for the electrical part and the nuances of installing a pneumatic system. It is important to know that refrigeration compressors are not designed for long-term idle operation without load, which requires the mandatory installation of a check valve and a receiver. A competent approach will allow you to create a reliable tool for painting, inflating tires or working with pneumatic tools.
Diagnostics and preparation of the compressor for work
The first step should always be a thorough visual and electrical diagnosis. Externally, the housing should not have through damage, dents or signs of severe corrosion, especially in the area of the lower bottom where oil accumulates. If you see rust, this is not a death sentence, but requires a more careful check of tightness after the first start.
To check the electrical part, you will need a multimeter. It is necessary to ring the motor windings through the contacts on the starting relay. Winding resistance must be within certain limits: usually the starting winding has a higher resistance than the working one. If the device shows an open circuit (infinity) or a short circuit (close to zero), then such a motor cannot be used - it will burn out when trying to start.
It is also important to check whether the motor shaft is jammed. When turned on, a working unit emits a characteristic hum and after a few seconds begins to pump air. If you only hear a humming sound, but there is no rotation, you may need to intervene in the mechanical part or replace the start relay. Start relay This is the weak link of the system, which is often the first to fail during prolonged downtime of the equipment.
⚠️ Attention: Before any manipulations with the electrical system, make sure that that the power cord is unplugged. Residual voltage in capacitors or improper wiring may result in serious electric shock.
Be sure to clean the external surface of dust and dirt. Dirt entering through the ventilation system (if provided for by the design of a particular motor) or settling on hot surfaces can cause overheating. A clean unit is easier to diagnose for oil leaks, which are a sure sign of depressurization.
Necessary tools and materials for assembly
To create a full-fledged compressor installation, one motor is not enough. You will need to assemble a whole set of components, each of which performs its own function. The basis of the design will be itself compressor unit, a receiver (a container for storing compressed air) and a control system.
Old gas cylinders from fire extinguishers or freon are often used as a receiver. They have the necessary strength and are already equipped with threaded holes. However, before use, such containers require careful preparation: removal of residual contents, sandblasting and painting to protect against corrosion.
To connect all the elements you will need copper tubes, high-pressure hoses, clamps and fittings. The electrical part will require a circuit breaker, wires with a cross-section corresponding to the motor power, and, possibly, a capacitor to facilitate starting. Copper tubes preferably plastic ones, as they better withstand heat and vibration.
List of necessary tools and materials:
- 🔧 Set of wrenches and screwdrivers for installing fittings.
- 🔌 Multimeter for checking the integrity of electrical circuits.
- 🛢️ Container for draining and changing oil (if the design allows).
- 🧶 Sealing tape (FUM tape) or thread for threaded connections.
- 🧰 Drill or screwdriver for attaching elements to the frame.
Electrical connection diagram
The electrical diagram for connecting the compressor from the refrigerator is relatively simple, but requires care. The main attention should be paid to the starting relay, which provides a short-term voltage supply to the starting winding. Without this element, the engine will only hum, but will not start.
The relay body usually has a connection diagram or contact markings (S, R, C or L, N). The contact Common (C) is a common wire, Run (R) goes to the working winding, and Start (S) to the starting winding. Errors in connecting these contacts can lead to burnout of the windings or breakage of the relay.
Nuances of the operation of the starting relay
Inside the starting relay there is a coil and a moving contact. When voltage is applied, current passes through the operating winding and the relay coil. The magnetic field of the coil closes the contact, supplying power to the starting winding. As soon as the motor picks up speed, the current drops, the magnetic field weakens, and the contact opens. Some modern relays use a posistor (thermistor) instead of a mechanical contact, which heats up and loses conductivity, breaking the starting winding circuit.>
For ease of control and system safety, it is recommended to install a thermal relay or thermal protection relay. It will turn off the power if the motor overheats, which often happens during intensive use of homemade installations. Also, a circuit breaker with an emergency stop button would not be amiss.
⚠️ Attention: A capacitor, if used in a circuit, can retain a charge even after being turned off. Before touching the contacts, be sure to discharge it through a resistor or a screwdriver with an insulated handle.
All electrical connections must be securely insulated. Vibration, which is inevitable when the compressor is operating, can loosen the twists or loosen the contacts in the terminal block. Use high-quality insulating materials and, if possible, secure the wires with clamps.
Installation of the pneumatic system and receiver
The pneumatic system is the “circulatory system” of your compressor. It starts from the compressor outlet and ends with the air consumer. The key element here is the check valve, which prevents air from returning back into the compressor after it stops.
If the check valve is not installed, the compressed air from the receiver will tend to escape through the compressor, spinning its shaft in the opposite direction. This creates a huge load on the engine the next time it is started and can lead to its breakdown. Check valve must be installed immediately after the compressor outlet.
The receiver functions as a buffer: it accumulates air, equalizes pressure and cools the compressed gas, promoting moisture condensation. The volume of the receiver is selected based on your needs: 10-20 liters are enough for inflating tires; for sandblasting or painting, preferably 50 liters or more.
The following must be installed on the receiver:
- 📊 Pressure gauge for visual monitoring of pressure in the system.
- 🚿 Safety valve that bleeds air when the permissible pressure is exceeded.
- 💧 Drain valve at the bottom point to remove condensate.
- 🔌 Outlet fitting for connecting a hose with a tap.
Connection of all elements The pneumatic system must be sealed. Use flax tow with paste or FUM tape to seal threaded connections. After assembly, test the system for leaks by pumping air and treating the joints with a soap solution.
Pressure setting and security system
Refrigeration compressors are capable of creating fairly high pressure, but their performance (the volume of air pumped) is limited. The standard operating pressure in the system is usually 6-8 atmospheres, although some models can pump up to 10-15 atmospheres. Exceeding the operating pressure is dangerous for the structure.
A pressure switch (pressure switch) is used to automate the work. This device turns on the compressor when the pressure in the receiver drops below the set minimum, and turns it off when the maximum is reached. Pressostat significantly prolongs the life of the engine, eliminating its idle operation and preventing overloads.
If you do not use automatic pressure switch, pressure control will have to be done manually, monitoring the pressure gauge. In this case, the safety valve takes on the role of the main defender. It must be adjusted or selected so that it opens at a pressure that is safe for the receiver, but exceeds the working one.
| Parameter | Description | Recommended value |
|---|---|---|
| Working pressure | Pressure at which the tool operates | 4 - 6 atm |
| Start-up pressure | Minimum compressor start threshold | 3 - 4 atm |
| Switch-off pressure | Maximum compressor stop threshold | 8 - 10 atm |
| Reset pressure | Emergency valve response limit | 12 - 15 atm |
Do not forget that air compression is accompanied by heating. The pipes and the compressor itself can become very hot. Ensure good ventilation at the installation site of the equipment and, if possible, organize forced cooling or natural convection.
Start-up, running-in and possible malfunctions
The first start-up of the assembled system is a crucial moment. Turn on the compressor without connecting to the receiver (if the design allows) or with the outlet valve open to check the direction of rotation and the presence of pressure. Make sure that there are no strong vibrations or extraneous knocks.
During operation, the compressor may make various sounds. A steady hum is normal. A knocking, grinding or sharp whistle indicates a malfunction. A common problem is wear of the valves in the cylinder head, which reduces performance. Wear of valves Often accompanied by overheating of the head and a drop in pressure.
During operation, monitor the level and condition of the oil. Although many refrigeration compressors are considered “maintenance-free” and do not have an oil dipstick, changing the oil in them is possible and sometimes necessary if the unit was overheated or moisture got into the system.
⚠️ Attention: If you notice that the compressor stops turning off when reaching maximum pressure, stop it immediately. A malfunction of the pressure switch or valve can lead to rupture of the receiver.
Typical malfunctions and methods for their elimination:
- 🔥 Overheating: Check ventilation, oil level and load on the system.
- 💨 Low pressure: Look for leaks, check the valves and condition of the piston rings.
- ⚡ Not starts: Check the voltage in the network, the integrity of the wires and the operation of the starting relay.
- 🔊 Noise and vibration: Tighten the mounting bolts, check the shock absorbers and bearings.
Is it possible to use the compressor without a receiver?
Theoretically, start the compressor without a receiver it is possible, but using it to work with a tool is extremely undesirable. Without a buffer tank, the air flow will pulsate, which will ruin the quality of the paint or the performance of the pneumatics. In addition, the compressor will turn on and off too often, which will quickly lead to wear of the starting relay and motor windings.
What kind of oil should be poured into the compressor from the refrigerator?
Hermetically sealed compressors are usually filled with special synthetic or mineral oil (for example, freon). When replacing, it is better to use the same that was drained, or specialized compressor oils (for example, KS-19 or analogues). The use of motor oil is allowed in extreme cases, but it can coke faster at high temperatures.
Why does the compressor get very hot during operation?
Heating to 70-90 degrees Celsius is normal for piston compressors. However, if the temperature exceeds 100-110 degrees, this is a signal of a problem. The reasons may be clogged air filters, faulty valves, low oil level or too high frequency of switching on due to leaks in the system.