Faced with a breakdown of a refrigeration unit, many craftsmen are considering replacing the compressor or using an old engine for household needs. Motor from a refrigerator It is a sealed unit that is capable of creating pressure and vacuum, which makes it useful for painting work, aerating ponds or inflating tires. However, before starting work, it is necessary to clearly understand that inside this unit there is high voltage and refrigerant that requires careful handling.
The starting process single-phase asynchronous motor differs from turning on conventional household appliances, since it requires correct switching of the windings and the mandatory presence of a starting element. Errors in the connection diagram can lead to instantaneous burnout of the windings or even explosion of the starting capacitor. In this article we will analyze in detail the structure of the compressor, contact identification methods and a step-by-step algorithm for safe starting.
To perform the work you will need a minimum set of tools: a multimeter, pliers, insulating tape and, possibly, a new starting relay if the standard one has failed. It is critically important before starting any manipulations to completely disconnect the unit from the 220V electrical network. Any actions with electricity carry the risk of electric shock, so neglecting safety rules is unacceptable.
Compressor design and principle of operation
Sealed compressor is an electromechanical unit where the engine and piston group are located in a single steel housing. There is no air inside the housing; it is filled with inert gas or freon vapor, which helps cool the windings during operation. The engine has two main windings: working and starting, which are wound with copper wire on the stator.
The working winding is designed to maintain rotor rotation after starting and occupies most of the stator slots. The starting winding is turned on only for a short time (usually 1-3 seconds) to create the initial magnetic field and spin up the shaft. Starting relay automatically opens the starting winding circuit when the engine reaches the required speed, preventing it from overheating.
Why Compressors cannot be kept in a horizontal position for a long time?
During long-term storage or transportation in a horizontal position, oil from the crankcase may leak into the cooling system circuit. This will lead to oil clogging of the capillary tube and failure of the compressor at the first start.
Some modern models use inverter motors, which are controlled by complex electronics, but in older refrigerators the classic circuit with a relay predominates. Understanding the difference between these types is important, since the methods for diagnosing and connecting them are radically different. Classic motors are more repairable and easier to adapt for other purposes.
Identification of contacts and winding continuity
The first step before connecting is to determine the purpose of the contacts coming out of the compressor housing. Usually there are three of them, and they are located in a triangle on a special block. To understand which contact is responsible for what, you need to use multimeter in resistance measurement mode (Ohm). Without this device, connecting the motor “at random” is strictly prohibited.
The dialing procedure begins with searching for a common wire. Measure the resistance between each pair of contacts. The pair with the least resistance indicates the run and start windings together, and the third contact will be common. Next, by measuring the resistance between the common contact and the other two, you will determine their purpose: where the resistance is greater - there is a starting winding, where less is the working winding.
☑️ Checking the compressor with a multimeter
If the multimeter shows infinity (open) or zero (short circuit) between any contacts or to the body, such the engine is faulty. It is also important to check that there is no breakdown on the housing: one probe is placed on the cleaned part of the housing, the other one on the contacts in turn. The arrow of the device should not move. Starting relay You should also check for the integrity of the contacts and the mobility of the core.
Connection diagram via the starting relay
The standard circuit for connecting a motor from a refrigerator involves the use of a standard or similar starting one relay It is this element that provides temporary activation of the starting winding. There is usually a marking on the relay body indicating where is the top and where is the bottom, which is important for the correct operation of the gravitational opening mechanism.
The connection is made as follows: the common wire (Common) is connected to one of the power terminals (for example, zero), and the phase wire goes through the starting relay to the working winding. The starting winding is connected to the corresponding relay contact. The colors of the wires may vary depending on the manufacturer, so you need to focus on resistance measurements, and not on the color of the insulation.
| Contact type | Designation on the diagram | Resistance (Ohm) | Function |
|---|---|---|---|
| Common | C | Sum Rwork + Rstart | Power entry point |
| Run | R | Smaller value | Main work engine |
| Start | S | Larger value | Rotor start |
| Earth | GND | Infinity | Protection from breakdown |
Posistor relays have no moving parts and work by heating a ceramic element, which loses conductivity. Induction opens due to a drop in current in the working winding. Replacing one type with another is not always possible and requires careful study of the characteristics.
Starting without a relay: emergency method
In situations where the original relay is faulty or lost, you can start the engine manually using a button or toggle switch. This method is suitable for short-term performance testing or use of the compressor in home-made installations, where the user plays the role of the relay. However, constant operation in this mode is not recommended due to the risk of overheating of the starting winding.
The circuit is simple: the phase is supplied to the working winding constantly, and to the starting winding through a normally open button. By pressing the button, you apply power to the starting winding, the motor begins to rotate. After 2-4 seconds, when the engine picks up speed, the button must be released. If the engine hums and does not spin, the time you hold the button can be slightly increased, but not more than 5 seconds.
⚠️ Attention: Holding the button for applying voltage to the starting winding for a long time will lead to its rapid burnout. The starting winding is designed for short-term operation (up to 3% of the engine operating time).
To automate the process, homemade compressors often use automotive time relays or special pressure switches that break the starting winding circuit when certain parameters are reached. This makes operation safer and more convenient. Induction motor sensitive to correct phasing, so experiments with switching wires should be carried out only with the power turned off.
Use of capacitors for starting
Sometimes for improvement starting characteristics or adapting the motor to work in non-standard conditions are used starting capacitors. They provide the phase shift required for starting and can be used as an alternative or complement to a mechanical relay. The capacitor capacity is selected experimentally or according to tables depending on the motor power.
The capacitor is connected in parallel with the starting winding. When started, it creates the necessary impulse and then turns off. Some circuits also use run capacitors, which remain in the circuit permanently, improving engine efficiency, but this is rarely used for refrigeration compressors. The main attention is paid to the capacitor voltage, which should be at least 300-400V.
When selecting a capacitor, it is important to consider that too large a capacitance will cause overheating of the windings, and too small will not allow the engine to start under load. The best option for household compressors with a power of up to 1 kW are capacitors with a capacity of 20 to 50 μF. The exact values depend on the specific engine model.
Safety measures and typical errors
Working with refrigeration equipment involves risks not only of an electrical nature, but also of a chemical nature. There is oil and refrigerant inside the system that can be harmful if burned or leaked. In addition, the compressor gets very hot during operation, which can lead to burns or ignition of nearby materials.
One of the most common mistakes is trying to start the engine with an inverted relay. In gravity relays, the core must move strictly vertically downward under the influence of gravity. If you flip the relay, the contacts will not open and the starting winding will burn out in a matter of seconds. Always check the position of the relay in relation to the motor housing.
⚠️ Attention: Never operate the compressor in a confined space without ventilation. The engine requires cooling, and if the housing is depressurized, refrigerant vapor will enter the air, displacing oxygen.
Also, beginners often confuse the contacts by connecting the phase to the starting winding directly without a relay. This causes humming, heating and lack of rotation. If the motor hums but does not start, immediately turn off the power and recheck the circuit. Short circuit protection in the form of a circuit breaker or fuse is required in the power circuit.
Adaptation of the compressor for other purposes
Old motors from refrigerators often get a “second life” in workshops. They are used to make compressors for airbrushing, vacuum pumps for molding or wheel inflation systems. To do this, a hose is connected to the outlet pipe (supercharger), and a filter is placed on the inlet pipe (suction). It is important to use hoses designed for oil and air pressure.
When using a compressor as a vacuum pump (for suction), it must be taken into account that it creates a vacuum, but is not intended for pumping out aggressive gases or water vapor. Moisture entering will cause corrosion and emulsification of the oil. For such purposes, moisture separators and fine filters are installed at the inlet.
For painting work, you definitely need a receiver (air tank) and moisture-oil separator. A refrigeration compressor produces a pulsating air flow with oil impurities, which is unacceptable for high-quality painting. Installing a receiver smooths out pulsations and a filter cleans the air. Without these elements, you cannot use a motor for a spray gun.
Is it possible to run a three-phase motor from a refrigerator in a single-phase network?
Three-phase motors are practically never found in household refrigerators; they are typical for industrial equipment. If you come across such a unit, to operate on 220V you will need a delta or star circuit with the connection of the working and starting capacitors. The power will drop to 70% of the nominal value.
Why does the compressor turn off a few seconds after starting?
This is a thermal protection relay triggered. Reasons: malfunction of the relay itself, jamming of the piston group, interturn short circuit in the windings or insufficient voltage in the network. This can also occur when operating without a vacuum load, if the system is not configured correctly.
What kind of oil should be poured into the compressor during refurbishment?
Only special compressor oils should be used (for example, Freon-24, 12XF12-18 or their modern analogues). Regular motor oil from a car is not suitable, as it can foam, coke upon contact with the refrigerant, or have the wrong viscosity for the rubbing vapors of the refrigerator.
Does the compressor housing get very hot during operation - is this normal?
Yes, for hermetic compressors the operating temperature of the housing can reach 70-90 degrees Celsius and even higher. They are cooled by pumped gas and natural convection. However, if the housing becomes red hot or emits a burning smell, this is a sign of a malfunction.
Is it possible to change the direction of rotation of the refrigeration motor shaft?
No, the design of the piston group and the lubrication system are designed for a strictly defined direction of rotation. Changing the direction (reverse) is only theoretically possible when the engine is completely rebuilt, but in practice hermetic compressors rotate only in one direction.