A sudden stop of the refrigerator is always stressful, because food supplies are at risk. If you notice that the engine hums, twitches, but cannot start, or the compressor is completely silent and the light in the chamber is on, the problem often lies in one small detail. This part is the starting relay, which is responsible for starting the engine and its normal operation in the first seconds.
Before calling a technician or rushing to the store for a new unit, it makes sense to carry out an initial diagnosis. In many cases relay malfunction you can identify it yourself using a minimal set of tools. Understanding the operating principle of this element will help you save time and money, as well as accurately determine whether your refrigerator needs to replace a part or the reason lies deeper.
In this article we will look in detail at how the start relay works, what symptoms indicate its failure and step by step we will describe the testing process. You will learn how to safely remove the assembly, what to look for during a visual inspection, and how to properly use a multimeter to accurately diagnose an electrical circuit.
The principle of operation and function of the starting relay
The starting relay is an electrical switch that automatically supplies voltage to the starting winding of the compressor only at the moment it starts. As soon as the motor rotor reaches the required speed, the relay opens the starting winding circuit, and the motor continues to operate on the main winding. Without this device, starting a single-phase asynchronous motor installed in household refrigerators would be impossible.
There are two main types of such devices: induction (electromagnetic) and posistor (thermal). Induction relays work on the principle of an electromagnet: when current is supplied, the armature is drawn in and closes the contacts starting winding. As the motor accelerates, the current drops, the magnetic field weakens, and the contacts open under the influence of gravity or a spring. Such models are often marked RTP or RTK and are typical for Soviet technology.
In more modern models, such as Indesit, LG or Samsung, posistor relays are more common. They are based on a thermistor (posistor), which, when voltage is applied, heats up sharply and increases its resistance, actually breaking the circuit. This process takes only a few seconds. Posistor is a more reliable and silent element that does not have moving mechanical parts.
⚠️ Attention: An attempt to start the compressor without a working relay or with shorted contacts can lead to burnout of the motor windings. Never leave your refrigerator plugged in if you suspect a problem with the start circuit.
Understanding your relay type is critical to proper diagnosis. If a mechanical relay can be “tapped” or the contact path can be checked, then such a number will not work with a posistor - it is checked exclusively for resistance and visual integrity. An error in determining the type of device can lead to false conclusions about its performance.
Typical symptoms of a relay malfunction
Diagnostics often begin with an analysis of the behavior of the refrigerator. If you hear the compressor trying to turn on, making a clicking sound, humming for a couple of seconds and clicking again, followed by silence, this is a classic sign of a problem in the starting circuit. The motor receives power, but cannot go into operating mode, and the thermal protection relay opens the circuit to prevent overheating.
In some cases, there is complete silence from the motor, although the power indicator on the panel is on. This may mean that the contacts inside the relay have oxidized or burned so much that current simply does not pass to the windings. Also, a malfunction may be indicated by a characteristic smell of burning or melted plastic in the compressor area.
- 🔊 Frequent clicks: The compressor constantly clicks every few minutes, trying to start, but to no avail.
- 🔥 Case heating: The side wall of the refrigerator or the compressor itself becomes hot, although it is cold in the chamber no.
- 💡 The machine is triggered: When you try to start the refrigerator, the circuit breakers in the apartment's electrical panel are knocked out.
- 👃 Burning smell: You can feel a specific smell of burning plastic or electrics near the back wall.
It is important to distinguish a relay failure from a malfunction of the compressor itself. If the relay is working properly, but the engine still does not start and hums, it is possible that the windings or the piston group are jammed. In such a situation, replacing the relay will not help, and a more complex repair or replacement of the unit will be required. turn-to-turn short circuit in the windings or jamming of the piston group. In such a situation, replacing the relay will not help, and more complex repairs or replacement of the unit will be required.
Preparation for diagnostics and safety precautions
Before starting any work with electrical appliances, you must strictly follow the electrical safety rules. The first and most important step is to completely disconnect the refrigerator from the electrical network. It is not enough to simply turn it off with a button; you need to unplug it from the socket. This will eliminate the risk of electric shock during disassembly.
To carry out high-quality diagnostics, you will need a minimum set of tools. First of all, this is a multimeter (tester) for measuring circuit resistance. You will also need a screwdriver (Phillips and flat-head), pliers and possibly a knife to strip the contacts. It would be a good idea to prepare a container with water and detergent to clean the relay of dirt before testing.
☑️ Tools for testing
Provide access to the compressor. To do this, the refrigerator must be moved away from the wall. If the rear panel blocks access to the motor, it must be removed by unscrewing the mounting screws. Be careful with copper pipes of the refrigeration circuit - they are thin and easily damaged if handled carelessly. Any deformation of the tubes may lead to a refrigerant leak.
⚠️ Attention: If you see traces of oil around the compressor or smell gas, stop work immediately and ventilate the room. A refrigerant leak in a confined space can be hazardous to health.
After removing the compressor protective casing (usually a plastic cap on the back of the motor), you will see the same start relay mounted on the compressor rod. It can be secured with a staple or simply held in place by a tight fit. Carefully remove it, remembering the position of the contacts and orientation in space.
Visual inspection and initial check
Before picking up the multimeter, conduct a thorough visual inspection of the removed device. Often external signs can immediately indicate a problem. Carefully inspect the relay housing for cracks, melting, blackening or traces of soot. If the plastic inside has turned black, it means that high-power sparking has occurred there.
For induction-type relays (with a movable core), mechanical stroke is important. Shake the relay near your ear: if the armature rattles inside or a knock is heard, it means the mechanism is broken. The contacts inside must be clean and smooth. If you see carbon deposits or pitting on the contacts, this indicates a poor connection and high contact resistance.
For posistor relays, visual inspection is also important. The posistor (tablet inside) should not have cracks or chips. If the ceramic element is crumbled, the device is definitely faulty. Also check the condition of the spring contacts that fit onto the compressor terminals - they should not be oxidized or weakened.
Is it possible to clean the relay contacts?
Yes, if the relay is inductive and the contacts are simply burnt, they can be carefully cleaned with fine sandpaper or a file. However, this is a temporary measure: the contact surface is broken, and after some time the sparking will resume with renewed vigor. It is better to replace the entire assembly.
Pay special attention to the condition of the wire insulation. If the braiding of the wires going to the relay has become stiff, cracked or melted, they must be replaced. The use of such wiring can lead to a short circuit. Insulation must be elastic and intact along the entire length.
Diagnostics with a multimeter: step-by-step instructions
The most accurate result is obtained by checking the electrical parameters using a multimeter. Switch the device to resistance measurement mode (Ohms), selecting a range of up to 200 Ohms or continuity mode. Before starting measurements, make sure that the probes are in good condition and the battery in the tester is charged.
Checking the induction relay occurs in two stages. First, test the main circuit: the resistance between the contacts going to the main winding should be close to zero (or fractions of an ohm), since it is just a conductor. Then check the starting winding circuit: in the normal position (vertically), the resistance should be zero.