The situation when the refrigerator stops freezing, and the compressor is silent or makes only short beeps, often forces the home mechanic to choose: call an expensive specialist or try to diagnose the problem on his own. One of the most common problems is the failure of the starting relay, which is responsible for starting the engine. In such cases, it becomes necessary to start the compressor directly to check its performance or use the unit in home-made projects, for example, to create a compressor for airbrushing or inflating tires.
However, before you take on the wires, you need to clearly understand that direct connection to a 220 volt network without protective automation carries risks. The refrigerator motor is an asynchronous motor that requires the creation of a rotating magnetic field to start. In normal mode, this is done by the starting winding through a relay, but in its absence, this function will have to be performed manually or using a temporary circuit.
In this article we will analyze in detail the design of the electric motor, safe starting methods and typical errors that can lead to burnout of the windings. You will learn how to identify contacts, what tools are needed for the job, and why starting relay it is still better to replace it with a working one, even if the temporary start-up was successful. Safety and understanding of physical processes are primary here.
⚠️ Attention: Working with 220V electrical voltage is life-threatening. Carry out all manipulations only with the equipment completely disconnected from the network. Make sure that the capacitors are discharged and your hands are dry.
Design and principle of operation of the compressor
For proper connection, you need to understand that inside the sealed casing there is an electric motor and a compressor part, sitting on a common shaft. The engine has two main windings: working (main) and starting. The working winding is wound with a thicker wire and has less resistance; it provides the main rotation of the shaft. The starting winding, which has a higher resistance and a smaller wire cross-section, is needed only to create the initial impulse of rotor rotation.
In the standard circuit, the starting winding is connected to the network for a short time (usually 1-3 seconds) through a starting relay. As soon as the engine picks up speed, the current in the circuit drops and the relay opens the contacts of the starting winding. If you remove the relay from the circuit, you will have to manually simulate this process: apply voltage to both windings to start, and then turn off the starting winding, leaving only the working one. If this is not done, the starting winding will burn out due to overheating, since it is not designed for long-term operation.
Modern models can be equipped inverter compressorswhich cannot be connected directly to a 220V network categorically. They require a complex electronic control unit (inverter) that converts alternating current to direct current and then back to variable frequency alternating current. The described method is only suitable for classic linear compressors with induction start, which were mass-produced in Soviet times and are still used in budget models.
It is also worth considering the presence of a capacitor in some circuits. Older refrigerators often used capacitor start relays, where the capacitor helped create the phase shift. With a direct connection without a relay, the presence or absence of a capacitor depends on the specific circuit, but most often for a short-term “wire” start, a capacitor is not required if you manually switch the starting winding.
How to distinguish an inverter compressor?
Inverter compressors usually do not have a starting relay at all, but are connected through an electronics board. The nameplate often reads "Inverter" or "Variable Speed". They cannot be started directly by wire.
Necessary tools and safety measures
Before starting work, it is necessary to prepare the workplace and tools. You will need a multimeter (tester) to test the windings and determine their resistance. Without this device, it is impossible to work “at random”, since the visual arrangement of contacts on different compressor models (ATM, Danfoss, Secop, Atlant) may differ. You will also need screwdrivers, pliers and insulating tape.
To create a temporary starting circuit, you will need a 220V power source. Ideally, this should be an outlet with a circuit breaker that will protect the wiring in the event of a short circuit. To switch wires, it is convenient to use a latching button or a regular toggle switch, but experienced craftsmen often use a simple circuit with two wires, closing them manually for a split second.
Pay special attention to the insulation of the connection points. Open twists 220V voltage is unacceptable. Use insulating tape or heat shrink. If you plan to use the compressor in a homemade device (for example, in a compressor installation for a garage), be sure to provide a housing to protect it from dust and moisture, as well as grounding the metal casing of the compressor.
- 🔌 A multimeter or ohmmeter to measure the resistance of the windings.
- 🧤 Dielectric gloves and tools with insulated handles.
- 💡 Incandescent lamp (control) or circuit breaker for short circuit protection.
- 🔧 Set of screwdrivers, pliers and insulating materials.
Identification of contacts and continuity of windings
The most critical stage is determining which pin on the compressor body belongs to which winding. Typically the contacts are arranged in a triangle. Many compressors have markings on them, but they may be worn off or filled with oil. Basic designations: C (Common) - common wire, R (Run) - working winding, S (Start) - starting winding. In European labeling this may look like 1-2-3 or C-R-S.
The identification process begins with a visual inspection. Look for a contact that is visually different or located separately (often a common wire). Then we take the multimeter to resistance measurement mode (Ohms). We measure the resistance between each pair of contacts. We need to find three values. The greatest resistance will be between the working and starting windings (total). The least resistance is the working winding (between the common and working contacts). The average value is the starting winding.
Consider an example: we have three contacts A, B, C.
Measurement A-B = 30 Ohm.
Measurement B-C = 10 Ohm.
Measurement A-C = 20 Ohm.
Sum 10 + 20 = 30. This means that A-C and B-C are separate windings, and A-B is the sum.
Contact C (common for both smaller measurements) is common wire.
Between C and B (10 Ohms) is the working winding (lower resistance).
Between C and A (20 Ohms) is the starting winding (higher resistance).
If the multimeter shows infinity (open) or zero (short circuit) between any contacts, the compressor is faulty and It's useless to connect it. Also check the resistance between any contact and the copper tube or housing - there should be infinity. If there is conductivity to the housing, the engine is broken, and it is dangerous to operate it.
☑️ Checking the compressor before starting
Schemes for direct connection to a 220V network
There are several ways to start the engine without a standard relay. The simplest and most common method is to use a button or toggle switch to momentarily close the starting circuit. To implement this circuit, you need to apply phase and zero to the common and working contacts constantly, and apply voltage to the starting contact only at the moment of start.
The connection diagram is as follows: one wire from the plug (for example, zero) is connected to the common contact of the compressor. The second wire from the plug (phase) goes to the working contact. A starting contact is connected parallel to this wire through a button. By pressing the button, you apply a phase to the starting winding, the engine hums and starts. As soon as you feel confident operation (after 1-2 seconds), you need to release the button.
A more advanced option is to use a capacitor. If you have a starting capacitor on hand (usually 20-50 µF for a voltage of at least 300V), it can be connected in series with the starting winding. However, for a short-term “wire” test, a capacitor is not necessary if you clearly control the switching time of the starting circuit. The main thing is not to overexpose the starting winding under voltage.
| Contact type | Resistance | Connection (Permanent) | Connection (Temporary) |
|---|---|---|---|
| General (C) | Average | Zero (N) | No |
| Working (R) | Minimum | Phase (L) | No |
| Start (S) | Maximum | No | Phase (via button) |
| Case | Infinity | Earth (PE) | No |
Step-by-step instructions for starting the engine
Now that the theory has been sorted out, let's move on to practice. Make sure that the compressor is secured vertically, since in a horizontal position it may not start due to lack of lubrication in the friction units or, conversely, oil may enter the system. Connect the wires according to the diagram described above, but do not plug the plug into the socket yet.
Take a button (or prepare insulated probes) to close the start contact. Plug in. The engine is still standing. Press the start button and you will hear a buzzing sound. If the engine is working properly, after a second or two it should start with a characteristic even hum. Release the button. If the engine continues to run, the circuit is assembled correctly.
If, after releasing the button, the engine stops or hums, but does not spin, there may be a problem in the mechanical part (jamming) or that the starting pulse was too short. Try increasing the time you hold the button to 2-3 seconds. If this does not help, and the current increases (the humming becomes stronger), immediately turn off the power - the motor is faulty.
For continuous operation in home-made devices, the button is replaced with an automatic time relay or a thermal relay from an old refrigerator is used, leaving only the starting group. But remember that without thermal protection, a long operating cycle can lead to overheating and burning of the windings.
⚠️ Attention: If the compressor hums but does not start for more than 3-5 seconds, turn it off immediately. Prolonged humming without rotor rotation leads to rapid overheating and melting of the winding insulation.
Typical faults and diagnostics
Even if the compressor has started, this does not guarantee its full serviceability. Listen to the sounds as you work. Metallic knocking, clanging or uneven hum may indicate a broken piston group or valves. If the compressor works, but does not create pressure (does not pump), a valve breakage or a crack in the housing is likely.
A common problem is thermal relay. Even with a direct connection, it can be in the working winding circuit. If it is faulty (open), the motor will not start. Check its resistance - it should be close to zero. If the relay gets hot and clicks, interrupting operation, it means that either the motor current consumption is higher than normal (mechanical wear), or the relay itself requires replacement.
It is also worth paying attention to the current consumption. The rating data (on the nameplate) usually indicates the rated current. If, when operating without load, the current is significantly higher than the rated current, this is a sign of an interturn short circuit in the windings or mechanical scuffing. The operation of such a unit will not last long.
- 🔥 The engine gets very hot - there may be an interturn short circuit or lack of freon (cooling).
- 🔨 A knock is heard inside the casing - destruction of the motor suspension or valve group.
- 📉 Low output pressure - worn rings or broken valves.
- ⚡ The circuit breaker knocks out - a short circuit in the windings or the starting current is too high.
Why is the compressor hot?
In normal operation, the housing The compressor must be hot (up to 80-90 degrees), since it is cooled by freon and oil. However, if it heats up to temperatures dangerous to touch in a matter of minutes, this is a sign of overload.
Using a compressor in homemade devices
Many craftsmen use old refrigeration compressors to create budget air compressors for aerography, tire inflation or pneumatic tools. In such cases, the standard relay is often replaced with more reliable automation or manual control is left if the operating cycles are short. It is important to understand that the refrigeration compressor is not designed for long-term operation in dry mode without freon, which cools the windings.
When remodeling, be sure to install a receiver (air tank) and a gearbox. This will smooth out pressure pulsations and reduce the load on the engine, reducing the number of engine starts. A moisture separator is also necessary, since the compressed air will contain condensation from oil and moisture, which can damage the instrument.
Do not forget about fire safety. Oil vapor mixed with air at high pressure and temperature can be explosive. Do not allow the outlet pipe to overheat above 160-170 degrees. Installing a thermal relay for emergency shutdown in case of overheating would be a reasonable solution for a homemade installation.
Is it possible to connect a compressor without a starting relay forever?
Theoretically, it is possible if you use a capacitor starting circuit matched to the engine power, but this reduces the efficiency and service life of the motor. The standard relay ensures optimal operation by turning off the starting winding at the right time. Working without it is possible as a temporary solution or in specific homemade products, but is not recommended for a standard refrigerator.
What to do if the compressor hums but does not start?
Most likely, the piston group is jammed or there is not enough voltage to create a starting torque. Try giving a short impulse to the starting winding (as described in the instructions). If it doesn’t help, you will need to repair the mechanical part or replace the compressor. Sometimes “wedging” helps by applying voltage to the working winding in antiphase, but this is a risky method.
What capacitor is needed for starting?
For most household refrigeration compressors with a power of 100-200 W, starting capacitors with a capacity of 20 to 50 μF with an operating voltage of at least 300V (better 400-450V). The exact value depends on the engine model and is indicated on its nameplate or in the technical documentation.
Is starting without a relay dangerous for the engine?
Short-term starting for diagnostics is safe. Prolonged operation without proper switching of the starting winding (if it remains energized) will lead to its burnout. If the circuit is assembled correctly (the starting circuit is turned off after start), then the risk is minimal, but the lack of thermal protection still increases the likelihood of failure due to overload.