How to connect a compressor from a refrigerator: diagrams and instructions

Using an old refrigeration compressor is a great way to get a source of compressed air for household needs without purchasing expensive factory equipment. Many craftsmen and home craftsmen successfully assemble spray guns, tire inflators, and even aeration systems for aquariums using such units. However, this process requires not only technical skills, but also a clear understanding of the principles of operation of electromechanics.

Before starting assembly, you need to make sure that the device itself is in working order. compressor. Not every component removed from a non-working refrigerator is suitable for reuse as a supercharger. It is important to check the motor windings, the condition of the starter and the tightness of the housing, since not only the performance of the future installation, but also your personal safety depends on this.

In this article we will analyze in detail all stages of preparation and connection, paying special attention to the electrical circuit and mechanical connection of the nodes. You will learn how to correctly calculate power, select a receiver and configure a protection system. A competent approach will allow you to create a reliable tool that will last for many years.

Diagnostics and preparation of the compressor unit

The first step in the modernization process is a thorough check of the unit being removed. You need to visually inspect the housing for deep dents, signs of corrosion or oil leaks, which may indicate a leak. If traces of rust are visible on the case case, especially in the lower part, using such a unit can be risky, since moisture could remain inside, causing corrosion of the piston group.

Electrical diagnostics are carried out using a multimeter. It is necessary to ring the three terminals coming out of the motor to determine the resistance of the windings. A normal state is considered when the resistance between the starting and operating windings, as well as between them and the housing, is within reasonable values ​​(usually from 10 to 60 Ohms, depending on the model).

⚠️ Attention: If the multimeter shows a short circuit to the housing (resistance is close to zero or infinity where the circuit should be), operating such a motor is strictly prohibited. This may result in electric shock or fire in the wiring.

It is also important to determine the type of starter. In older models, a starting relay with a posistor or a mechanical relay with a coil is often found. For operation outside the refrigeration cabinet, the standard relay may not work correctly due to changes in temperature conditions, so sometimes it is necessary to replace it with a more universal analog or forced start through a capacitor circuit.

Necessary tools and materials for assembly

For high-quality assembly of the compressor unit, you will need not only the unit itself, but also a number of additional components. The main element of the system will be receiver a container for accumulating compressed air, the role of which is often played by an old gas cylinder or fire extinguisher. The volume of the receiver directly affects the stability of pressure and the frequency of engine start-up.

In addition to the container, stock up on high-quality high-pressure hoses, fittings, a pressure gauge and a check valve. The check valve is a critical element that prevents air from returning from the receiver to the compressor after stopping the engine, preventing the shaft from spinning in the opposite direction and oil from entering the system.

Electrical diagram for connecting the motor

Connecting the electrical part is the most critical stage that requires care. A standard refrigerator compressor has three terminals: common, starting and working. To start the engine outside the standard refrigerator circuit, a circuit with a starting capacitor is often used, which briefly supplies an impulse to the starting winding.

It is necessary to clearly identify the contacts. Usually the common wire has the greatest resistance relative to the others, but it is better to look for exact data in the technical documentation for the specific model motor. Incorrect connection can lead to winding burning or humming without shaft rotation.

A thermal protection relay must be included in the circuit. It monitors current consumption and turns off power when the shaft is overloaded or jammed. Without this element, the risk of failure of an expensive unit or a fire increases significantly.

⚠️ Attention: Carry out all electrical connection work only with the power supply from the 220V network completely disconnected. Residual voltage in capacitors can be dangerous.

Mechanical assembly and installation of the receiver

The mechanical part of the assembly consists of securely fastening all components to a common frame and sealing the pipelines. The compressor and receiver must be firmly fixed so that vibrations during operation do not loosen the connections. To reduce noise and vibration, rubber gaskets are often used under the engine feet.

The compressor is connected to the receiver through a check valve and a shut-off valve. This allows the drive to be disconnected during maintenance. It is better to make pipelines from copper tubes or reinforced hoses, securing them with clamps.

It is important to provide for condensate drainage. A tap or automatic condensate drain is installed at the lowest point of the receiver. Moisture contained in the compressed air will settle at the bottom of the tank, and if not removed, it can get into the tool or cause corrosion of the tank from the inside.

Calculating pressure and setting up the system

Refrigeration compressors are not designed to create high pressure, like specialized air pumps. Their operating range is usually limited to 6–8 atmospheres, although for a short time they can raise pressure higher. Exceeding the permissible values ​​can lead to rupture of seals or damage to valves.

To control the pressure, a reducer and a pressure gauge are built into the system. The reducer allows you to reduce the outlet pressure to the required value for a specific tool, for example, an airbrush requires about 2-3 atmospheres, and to inflate tires - a little more.

Why can’t you pump up to 20 atmospheres?

Refrigeration compressors have a weak lubrication and cooling system. At high back pressure, the discharge temperature rises sharply, the oil cokes, and the compressor seizes or catches fire.

The system should be set up with minimum pressure values, gradually increasing the load and monitoring the temperature of the engine housing. If the engine begins to heat up excessively, it is necessary to reduce the operating pressure or increase the pause time between operating cycles.

Table of technical characteristics and compatibility

When choosing a compressor for conversion, it is important to take into account its initial parameters. Different models have different performance and permissible pressure. Below is a table with approximate data for popular types of units.

Please note that inverter compressors, which are becoming increasingly popular in modern technology, are extremely difficult to use for such purposes. They require complex electronics to control the speed and often have a built-in control system that is difficult to bypass without in-depth knowledge of electronics.

Frequent errors and safety precautions

One ​​of the most common mistakes is ignoring the need to filter the air at the inlet. The atmospheric air contains dust, which, when entering the cylinder, acts as an abrasive, quickly wearing out the piston group. Installing a simple air filter from a car or a special filter at the inlet will significantly extend the life of the device.

Another mistake is the lack of a cooling system. When operating for a long time, the compressor becomes very hot. If you plan intensive operation, it is worthwhile to provide forced cooling of the engine with a fan or increase the radiator area. Overheating leads to oil dilution and loss of compression.

⚠️ Attention: Never leave a running compressor unattended for a long time. If the valve jams or the automation fails, this can lead to an explosion of the receiver.

It is also worth mentioning the oil. Only the oil recommended by the manufacturer or its high-quality analogues should be filled into the compressor crankcase. Mixing different types of oils can lead to the formation of sediment and coking of the channels. Regularly checking the level and changing the oil is the key to long service life of the mechanism.

Is it possible to use a compressor without a receiver?

Technically, you can start the compressor directly, without a receiver, but it will work in pulse mode, creating flow pulsations. This is acceptable for inflating tires, but for painting or working with pneumatic tools, a smooth air flow is required, which is provided by the receiver. In addition, operation without storage causes the motor to turn on and off too often, which quickly wears out the start relay and windings.

How long can a compressor run without interruption?

Refrigeration compressors are not designed to operate at 100% load (100% duty cycle). The optimal operating mode is 50% (for example, 10 minutes working, 10 minutes resting). During continuous operation for more than 30-40 minutes, the housing temperature can reach critical values, which will lead to thermal breakdown of the winding insulation or jamming of the piston group due to metal expansion.

What kind of oil should be poured into the compressor?

In most cases, special synthetic or mineral compressor oil for refrigeration machines is used (for example, Freon oils). As a last resort, for short-term work in air, you can use high-quality motor oil, but it oxidizes faster and forms carbon deposits. It is strictly forbidden to use vegetable oils or waste, as they quickly turn into tar.

Why does the compressor hum but does not start?

This is a classic sign of a faulty starting device or low voltage in the network. Most often, the starting relay or starting capacitor fails, which does not provide the necessary torque to break the piston from its place. Also, the cause may be jamming of the piston group due to lack of oil or moisture entering the system.