A situation where the refrigerator suddenly stops cooling, and only a quiet hum or click is heard inside, often indicates a malfunction of the starter mechanism. In most cases, owners of household appliances are faced with the fact that starting relay, which is responsible for starting the engine, has failed, while the compressor itself may be absolutely fine. Understanding how to start a refrigerator engine without a relay is a key skill for a technician trying to carry out initial diagnostics of the unit on site.
However, it is worth immediately defining the boundaries of what is permissible: direct connection of the motor to the electrical network without automatic protective equipment is an emergency measure necessary solely to check the functionality of the unit. It is strictly forbidden to operate the refrigerator in this mode all the time, since the lack of protection will lead to rapid overheating of the windings and eventual failure of the expensive compressor. In this article we will analyze in detail the theoretical foundations of the operation of a single-phase motor, the connection diagram and safety precautions when carrying out diagnostic work.
⚠️ Attention: All work on connecting the compressor should be carried out only when the power supply is disconnected from the mains. Connecting 220V voltage to open contacts carries a mortal danger to life.
The principle of operation and the design of the trigger mechanism
For successful diagnosis, it is necessary to understand what exactly we are excluding from the circuit. Standard refrigerator compressor is an asynchronous electric motor, which requires a phase shift to start rotating the rotor. In household models, this task is performed by the starting winding, which is activated only for a short time - a fraction of a second required to accelerate the shaft.
Responsible for controlling this process is starting relay, which can be induction (electromagnetic) or posistor. At the moment of switching on, the current in the working winding increases sharply, the magnetic field draws in the relay core, closing the contacts of the starting winding. As soon as the rotor picks up speed, the current drops and the relay opens the starting winding circuit. If the relay is faulty, the engine either hums, but does not start, or starts, but immediately knocks out the circuit breaker.
That is why starting the engine without a relay implies that the master must manually or using an auxiliary circuit simulate this short-term impulse. Without this critical stage, the rotor will remain stationary, and the windings will begin to heat up from the high starting current, which will quickly lead to turn-to-turn short circuit.
What is the difference between a posistor and induction relay?
An induction relay works due to an electromagnet that draws in core at high current. A posistor relay uses a ceramic element (posistor), which is heated by current and changes its resistance, opening the circuit. The posistors require time to cool down (3-5 minutes) before turning them on again.
Required tools and precautions
Before starting to manipulate the electrical part, it is necessary to prepare the workplace and tools. You will need a multimeter to check the integrity of the windings, insulating tape, a screwdriver to remove the casing and, ideally start button with normally open contacts or a piece of wire with a plug for a short circuit. It would also be useful to have ( - pliers) with insulated handles.
Safety is priority number one. The compressor often has a metal casing, which can become energized if the insulation breaks down. If you are testing outside the refrigerator enclosure, make sure the motor is securely fastened and grounded. Any work with connected power should be carried out with one hand to exclude the possibility of current passing through the heart in the event of a shock.
☑️ Safety check before starting
It is also important to consider the condition of the motor itself. If the compressor makes gurgling noises or has been upside down and transported in an incorrect position, it should not be started without first standing upright for several hours. Oil that gets into the circuit can create a water hammer or clog the capillary system.
Diagnostics of windings before connection
The most common mistake when trying to start is ignoring a preliminary check of the hardware. Before applying voltage, you need to test the windings with a multimeter. The compressor terminal block usually has three contacts: two upper and one lower (or three in a row, depending on the model Danfoss, Atlant or LG). It is necessary to find a “common” wire whose resistance to other contacts will be the least.
The test algorithm is as follows:
- 🔍 Searching for a common wire: Measure the resistance between all three pairs of contacts. The pair with the highest resistance is the start and run windings together. The third contact, not involved in this pair, is the “common” (Common).
- 📏 Definition of the starting winding: Between the common wire and one of the others, the resistance will be higher (usually 20-40 Ohms). This is the starting winding.
- ⚙️ Determination of the working winding: Between the common wire and the remaining contact, the resistance will be lower (usually 10-15 Ohms). This is the working winding that consumes the main current.
- 🚫 Checking for breakdown: Make sure that none of the contacts rings on the compressor housing. If the multimeter shows resistance between the contact and the copper tube, the motor is faulty.
If the resistances differ greatly from the nominal values or show infinity (break), there is no point in starting the engine - it has burned out. It is also worth checking the condition of the capacitor, if it is provided for in the design of your model, although most modern household refrigerators use circuits without capacitor start.
| Winding type | Resistance (Ohm) | Contact location | Function |
|---|---|---|---|
| Running | 10 - 15 Ohm | General ↔ Working | Main rotation |
| Starting | 20 - 40 Ohm | General ↔ Starting | Starting impulse |
| Total | 30 - 55 Ohm | Working ↔ Starting | Full circuit |
| To the case | ∞ (Infinity) | Any ↔ Case | Isolation |
Direct start circuit and step-by-step instructions
After successful diagnostics, you can proceed to the practical part. To start, we need to supply 220V to the common wire and the working winding constantly, and to the starting winding only at the moment of start. Since we do not have a relay, its function will have to be performed manually or using a button. The connection diagram looks like this: the phase wire of the network goes to the common contact of the compressor, and also through the button to the starting contact. The neutral goes to the working winding (or vice versa, depending on the phasing, but for an asynchronous motor this is not critical).
The starting process is as follows:
1. Connect the wires to the compressor contacts according to the diagram. Make sure that the contacts are securely fixed; you can use clamps or high-quality twisting with electrical tape.
2. Plug the plug into the outlet. The engine will not stop for now, since the starting winding circuit is open.
3. Press the start winding connection button. You will hear a hum, and after 1-3 seconds the engine should start, changing the hum to a more even one.
4. As soon as the motor has gained momentum, the start winding button is necessary release immediately. If you hold it for more than 3 seconds, the starting winding will burn out.
If the engine does not start the first time, let it cool for 10-15 minutes. Repeated attempts to start a hot compressor can lead to jamming of the piston group due to thermal expansion of the metal. In some cases, if the compressor has not been working for a long time, it may be necessary to briefly apply voltage to the starting winding several times (pulses) to move the rotor, but this must be done extremely carefully.
⚠️ Attention: The time of applying voltage to the starting winding should not exceed 3 seconds! Prolonged exposure to current will lead to overheating and melting of the insulation of the starting winding.
Analysis of results and possible malfunctions
Successful starting of the engine does not guarantee its full serviceability. It is necessary to analyze the nature of the compressor operation. If it starts, but operates with strong vibration noise, knocks or hums louder than usual, this may indicate mechanical wear of the liners or valve group. It is also worth paying attention to the current consumption: if you have a current clamp, measure the current strength. It should not exceed the nominal values indicated on the nameplate (usually 0.5 - 1.0 A for household models).
The table below shows the main symptoms and their probable causes when starting without a relay:
| Symptom | Probable cause | Actions |
|---|---|---|
| Buzzing, won't start | Stuck, low voltage | Check the voltage, try starting with an external starting winding |
| Starts and stalls immediately | Valve malfunction, breakdown | Check outlet pressure, insulation breakdown test |
| Strong vibration | Bearing wear, spring breakage | Replacement of the compressor (repair is economical impractical) |
| Housing heating | Lack of freon, condenser contamination | Check the cooling system, clean the radiator |
If the compressor starts but does not create pressure (does not blow from the outlet tube), the problem may not be electrical, and in the mechanical part - valve failure. In this case, replacing the relay or even the motor itself (if you take a used one with the same fault) will not help. A full diagnostic of the refrigeration circuit is required.
Why you can’t operate a refrigerator without a relay
Many users, having successfully started the motor with a button, ask the question: “Is it possible to leave it like that and use it?” The answer is categorical: no, you can’t. The start relay performs two functions: it starts the engine and, more importantly, protects it. In normal mode, the relay opens the starting winding immediately after gaining speed. If you leave the circuit closed or use a “crutch” in the form of a jumper, the starting winding will burn out after a few minutes of operation.
In addition, a thermal relay (often combined with the starting one in one housing) protects the motor from current overloads. If high pressure occurs in the system (capillary is clogged, there is a lot of freon) or a voltage surge occurs, the current in the windings will increase. The standard relay will open the circuit and save the motor. With a direct connection, the motor will run until the insulation burns or the piston group jams. This is a fire hazard and not economically profitable.
It is also worth considering that modern inverter compressors (found in models Liebherr, Bosch, LG with the Linear Inverter system) cannot be started in this way at all. They are controlled by a complex electronic unit that generates a three-phase voltage of a certain frequency. A direct supply of 220V 50Hz will kill such a compressor instantly. The button method is applicable only to classic asynchronous motors.
⚠️ Attention: Inverter compressors cannot be started by direct connection to a 220V network! To diagnose them, a special tester or a working main control unit is required.
Frequently asked questions and answers (FAQ)
Is it possible to start a three-phase compressor from a single-phase network without a relay?
Technically it is possible using a capacitor circuit starting, but three-phase motors are practically not used in household refrigerators. If we are talking about industrial refrigeration equipment, then the connection diagram is more complicated and requires selecting the capacitor capacity according to formulas depending on the engine power.
How many times can you try to start the compressor?
It is not recommended to make more than 3-5 attempts to start in a row. Between attempts, be sure to take a break of 10-15 minutes to cool the oil and equalize the pressure in the system. Frequent “pull” starts can completely jam the compressor.
It hums, but does not start even with the button. What's the matter?
Most likely, the compressor is mechanically jammed (scuffing in the cylinders, destruction of the liners) or an interturn short circuit has occurred in the windings. The reason may also be a lack of refrigerant in the system, although usually in this case the compressor works but does not cool. Try to gently tap the housing with a hammer through a wooden gasket at different points when voltage is applied - sometimes this helps to remove a jammed piston.
What is the service life of the compressor after such an emergency start?
If the compressor was working properly and you simply checked its performance, the service life was not affected. However, if you operate it without a standard relay for a long time, the resource is reduced significantly due to the operation of the starting winding in the wrong mode and the lack of thermal protection.
Is it possible to use a car battery for starting?
No, refrigerator compressors operate on alternating current (AC) 220V. A car battery produces direct current (DC) 12V. The connection will only lead to the creation of a powerful electromagnet, but there will be no rotation, and the battery will quickly run out or fail.