How to start a refrigerator compressor without a relay: step-by-step instructions

Sometimes in the process of diagnosing refrigeration equipment occurs there is an urgent need to check the serviceability of the motor itself, excluding external controls from the chain. A situation where it is required start the compressor directlymay arise when a faulty start-up relay or thermostat is suspected. This is a temporary testing measure to determine whether the “heart” of your refrigerator is alive, or whether the problem lies deeper. However, it is worth immediately noting that such an operation requires compliance with strict electrical safety measures, since you are working with open live parts under high voltage.

In domestic conditions, this method is most often used by craftsmen for express diagnostics, when there are no spare components at hand, and the result is needed immediately. Start relay is a device that briefly supplies current to the starting winding of the motor to create torque, and then opens the circuit. If it burns out, the engine hums but does not start. Connecting without a relay allows you to artificially simulate this process. It is important to understand that long-term operation of the refrigerator in this mode is strictly prohibited, as this can lead to overheating of the windings and failure of the expensive unit.

Before starting any work, it is necessary to de-energize the device and prepare the tool. You must be clearly aware of the risks: electric current it is life-threatening, and the wrong sequence of actions can finally finish off a compressor that is still working. In this article, we will analyze in detail the physics of the process, the wiring diagram and nuances that will help you avoid fatal errors when carrying out a diagnostic startup.

The principle of operation and the design of the trigger mechanism

To successfully carry out the startup procedure, you need to understand what exactly we are bypassing. The refrigerator motor is an asynchronous electric motor with two main windings: working and starting. The working winding creates the main magnetic field that ensures the rotation of the rotor, but it lacks the initial impulse to start. This is where start windingcomes in, which only turns on for a split second at the moment of switching on.

A standard start-up relay performs two critical functions. The first is the supply of voltage to the starting winding at the moment of start and its subsequent shutdown when the rotor reaches the required speed. The second function is thermal protection: inside the relay there is a bimetallic plate that opens the circuit when the motor overheats or when the rotor is jammed. By turning off the relay, you remove this protection, so control of the process falls entirely on your shoulders.

Why does the relay click when it breaks?

If the relay malfunctions, the contacts may stick or, conversely, not close. A characteristic clicking sound often means that the starting winding is receiving current, but the motor cannot turn over, or the relay is trying to operate, but due to a calibration violation, it immediately opens the circuit.

There are two main types of relays that you may encounter: induction (with a coil and a moving core) and posistor (where a thermistor plays the role of a switch). In both cases, the essence is the same: to ensure the start and protect the motor. When manually starting without a relay, you will have to take on the role of this mechanical or electronic switch, giving the impulse strictly manually.

Necessary tools and precautions

Preparation of the workplace is the key to success and safety. You don't need a complex industrial tool, but the set should be complete. First of all, make sure you have a working power supply with a plug and button, or use the stock refrigerator cord, which will have to be modified. To work with wires, you will need wire cutters, pliers and high quality insulating tape.

Pay special attention to insulation. Since you are working with 220 volts, any exposed twists are unacceptable. Ideally, use terminal blocks or special clamps. You should also have a multimeter on hand to check the integrity of the windings before starting - this will help avoid a situation where you supply current to an already burnt-out motor.

⚠️ Attention: It is strictly forbidden to touch the metal parts of the compressor and wires while applying voltage. The risk of electric shock is extremely high, since the motor housing may be energized if the insulation breaks down.

List of required equipment:

• 🔌 A working power cord with a plug or a ready-made power supply for tests.
• ✂️ A tool for stripping wires (stripper or knife).
• 🧤 Dielectric gloves for additional hand protection.
• 🔦 Flashlight for good illumination of the work area in hard-to-reach places.

Diagnostics of windings before connection

Before trying to turn the motor shaft manually or apply current, it is necessary make sure the electrical circuit is intact. Take your multimeter and switch it to resistance (Ohms) measurement mode. On the compressor body you will find three terminals, usually hidden under a plastic cap. The terminals can be arranged in a triangle or in a row.

You need to call each pair of contacts. There must be a certain resistance between the working and starting windings, as well as between each of them and the common wire. Typically, the resistance of the working winding is less (about 10-30 Ohms), and the starting winding is higher (30-80 Ohms). If the device shows infinity (open circuit) or zero (short circuit), then starting such a motor is useless and dangerous - it requires replacement or rewinding.

It is also critical to check the resistance between any terminal and the copper tube or compressor housing. Here the multimeter should show infinity (one in the most significant digit). If there is at least some resistance value, it means that the insulation inside the motor is broken, and it cannot be operated - this will lead to an electric shock when touching the refrigerator body.

Table of typical resistance values for different types of compressors:

Connection diagram and procedure

The most critical stage is the direct connection of the wires. You need to determine which pin corresponds to the working winding, which is the starting winding, and which is the common one. Typically the common wire (C or COM) has the lowest resistance relative to both others. The working winding (R) has less resistance relative to the total than the starting winding (S).

To start without a relay, the method of briefly applying voltage to the starting winding is used. The circuit is simple: one wire from the network (phase) goes directly to the common terminal of the compressor. The second wire (zero) goes to the working winding constantly. The third wire, which will perform the starting function, must be short-circuited to the starting winding at the moment of switching on.

The action algorithm is as follows:

1. Fix the compressor in a vertical position so that oil does not enter the circuit.
2. Connect a constant circuit (phase to common, zero to working).
3. Turn on the power supply - the motor should hum, but not start.
4. Touch the starting winding output to 1-2 with the free wire seconds.
5. If the start is successful, release the starting wire - the motor will continue to work.

If, after applying a pulse to the starting winding, a sharp click is heard and the buzzing stops, it means that the internal protection has tripped or the motor is jammed. It is not recommended to repeat the procedure more than three times in a row; let the compressor cool for 15-20 minutes.

Nuances of starting different types of compressors

Not all motors are the same, and the approach to them may differ. Older models of refrigerators were often equipped with compressors with induction-dynamic start, where the relay operated due to the current in the coil. Modern units, especially those marked BLDC or inverter, cannot be started in this way. They require a complex electronic control unit (inverter), which generates the frequency and phase of the current.

For inverter models, the “direct start” method described above will not work, since their motors are three-phase and controlled by a microprocessor. An attempt to supply 220 volts directly to them will lead to burnout of the stator windings. Therefore, before you start experiments, make sure that you have a classic single-phase asynchronous motor.

⚠️ Attention: Inverter compressors (often found in LG, Samsung, Bosch models of recent years) cannot be started without a native electronic control module. This method is applicable only to classic piston compressors.

It is also worth considering the engine power. Low-power units can start even from a weak impulse, while powerful two-compressor systems require precise timing. If you overextend the starting wire, the starting winding may burn out, since it is not designed for long-term operation under load.

Frequent errors and possible consequences

One ​​of the most common errors is a violation of the orientation of the compressor. The motor must stand strictly vertically, as it is installed in the refrigerator. If you tilt it during operation, oil from the crankcase may enter the discharge tube and then into the cooling circuit. This will lead to clogging of the capillary tube and the need for complex repairs of the entire system.

Another mistake is ignoring the heating of the housing. When operating without a relay and without a standard cooling system (which in the refrigerator is provided by air flow around the coils), the motor heats up very quickly. The duration of the test run should not exceed 30-40 seconds. If you hold your hand on the case and feel that the temperature is becoming uncomfortable, turn it off immediately.

Incorrect determination of the winding terminals is also fatal. If you mix up the working and starting windings, the engine may hum, heat up, but not rotate, or rotate in the opposite direction (which for a piston compressor means no pressure). Always double-check the resistance with a multimeter before applying voltage.

The consequences of errors can be as follows:

• 🔥 Burnout of the starting winding due to a long current supply.
• 💥 Insulation breakdown and short circuit in the network.
• 🛑 Jamming of the piston group due to dry operation or in the wrong position.
• ⚡ Electric shock to the operator due to careless handling.

When professional repair is necessary

If after all attempts the compressor is humming, but it does not start even with a kick (manual impulse), most likely the problem is mechanical. This may be jamming of the piston group due to the exhaustion of its service life or the ingress of solid particles into friction units. At home, it is almost impossible to “unwrap” such a motor; the unit needs to be replaced.

It is also worth considering calling a specialist if you are not confident in your knowledge of electrical engineering. Refrigerator repair is not only about electrical work, but also about working with refrigerants. If during the diagnostic process you damage the tubes and release freon, a simple compressor replacement will turn into an expensive refill of the system with evacuation.

Is it possible to bypass the relay?

No, you cannot leave the refrigerator to operate without a start-up relay. This will cause the windings to burn out during the next start-up or overheat, which can cause a fire. A relay is a mandatory safety element.

Remember that the described method is exclusively a diagnostic procedure. It allows you to make a decision: change the compressor or look for a fault in other components (thermostat, relay, wiring). After a successful test, be sure to install a new, serviceable start-up relay that matches your engine model.

Is it safe to start a compressor without a relay in an apartment?

It's risky. In addition to the risk of electric shock, the compressor produces loud noise and vibration. There is also a possibility of oil splashing from the open pipe if it is not plugged. Do this only in a well-ventilated area and on a stable surface.

Why does the compressor start, but after 10 seconds it turns off?

Most likely, the thermal protection relay inside the motor itself is triggered (if it is built into the housing) or you do not hold the starting winding long enough, and the engine does not pick up speed. Also, the cause may be low voltage in the network.

Is it possible to use a starting capacitor instead of a relay?

Yes, a starting capacitor of a certain capacity can help create a phase shift for starting. However, its capacity must be selected experimentally, and it also requires a shutdown circuit after startup, otherwise it will burn out.

What resource does the compressor have after such a startup?

One ​​short-term diagnostic start does not affect the resource. But if you operate the refrigerator in this mode constantly, the motor will burn out in a few days or even hours due to the lack of protection against overheating and overloads.