A sudden stop of the refrigerator or a characteristic hum of the motor, which abruptly ends with a click, often indicates problems in the engine starting circuit. In such a situation, the owner of household appliances has to solve a difficult dilemma: call a technician or try to fix the problem yourself. One of the most common causes of failure compressor is the failure of the start-up relay, which is responsible for supplying voltage to the starting winding and protecting the motor from overloads.
The diagnostic process of this unit does not require deep knowledge of electrical engineering, but requires the presence of a basic tool, including in particular multimeter. Knowing how to do it correctly ring the relay allows you to save a significant amount on calling a specialist and purchasing an expensive new unit if it turns out that the problem can be solved by replacing a cheap element. However, it is worth remembering that working with electrical devices under voltage requires strict adherence to safety precautions.
In this article we will examine in detail the design of the starter mechanism, the algorithm for checking it and typical signs of a malfunction. You will learn how to distinguish a burnt coil from stuck contacts and what to look for during a visual inspection. Correct diagnostics is the first and most important step to restoring the performance of your refrigeration unit.
Design and operating principle of a start-up protection relay
The start-up protection relay is an electromechanical device that is installed directly on the compressor housing or connected to it through a short wiring harness. Its main task is to briefly connect the starting winding of the electric motor at the moment of start, when maximum torque is required to overcome the inertia of the piston group. After the rotor reaches the required speed, the device automatically turns off the starting circuit, leaving only the main winding to work.
Structurally, most of these relays are divided into two main types: induction and posistor. Induction models, often called “tablets” because of their characteristic shape, operate on the principle of electromagnetic induction. Inside them there is a movable core with contacts, which, under the influence of current, is drawn into the coil, closing the circuit. Posistor relays, more modern and common in refrigerators in recent years, use a special ceramic element (posistor), the resistance of which increases sharply when heated, which actually breaks the circuit of the starting winding.
An important design element is also thermal protection, which is often built into the relay housing or located next to it. It reacts to a critical increase in temperature or current, opening the contacts and preventing combustion of the motor windings. If your refrigerator hums, but does not start, or starts and immediately stalls with a click, most likely the problem lies precisely in the mechanical part of this unit or in the burnt-out posistor.
Understanding the internal structure helps to quickly determine the type of malfunction. In induction relays, contacts often burn out or the movable core jams, and in posistor relays, the ceramic element itself cracks or the contact at the soldering site is broken. A visual inspection of the inside of the device often provides more information than an external examination of the case.
Preparation for diagnostics: tools and safety
Before starting the inspection, it is necessary to ensure complete safety of the work. A refrigerator is a powerful electrical appliance that runs on 220 volts, so the first step should always be to completely disconnect the device from the power supply. It is not enough to simply turn it off with a button; you must physically remove the plug from the socket. Only after this can you remove the rear access panel to the compressor.
To carry out high-quality diagnostics, you will need the following set of tools:
- 🔌 Multimeter (tester) - the main device for measuring resistance and checking the integrity of circuits.
- 🪛 Set of screwdrivers - for removing the protective casing and dismantling the relay itself.
- 🧤 Dielectric gloves - for additional protection when working with electrical components.
- 🔦 Flashlight - for better illumination of the working area in the compressor area.
After removing the protective casing (usually a metal or plastic cap at the bottom of the refrigerator), you will see compressor and a relay attached to its contacts. Carefully remove the retaining bracket or bar holding the relay in place and disconnect it from the motor terminals. Be careful: the contacts may be oxidized, and sudden tugging may damage the terminals. Before you begin ringing details, carefully inspect the wires for melting or mechanical damage to the insulation.
⚠️ Attention: Never try to remove the relay or touch the compressor contacts while the device is plugged in. Even after disconnecting, it is recommended to wait a few minutes for the capacitors to discharge, if they are present in the control circuit.
If there are visually no traces of burning on the wires, and the terminals are not deformed, you can proceed to an instrumental check. It is also important to remember or photograph the position of the wires before disconnecting them, so as not to reverse the polarity during assembly, although for many types of relays this is not critical, but it is better to be safe.
Visual inspection and initial assessment of condition
Experienced technicians begin diagnostics not with a multimeter, but with a careful visual analysis. Often external signs can immediately indicate the nature of the breakdown. Take the removed relay in your hands and shake it thoroughly near your ear. If a characteristic knock is heard inside, similar to the rattling of bolts in a can, this is a sure sign of destruction of the internal components. In good condition, the core or posistor should fit tightly and not make sounds when shaken.
Next, you should inspect the inside of the device. To do this, depending on the design, you may need to carefully open the plastic case or simply look inside through the technological holes. Pay attention to the color of the contacts: they should be light, metallic. The presence of black soot, soot or melted plastic indicates that a short-circuit current or long-term overload passed through the contacts. Soot on the contacts increases the resistance and prevents normal engine starting.
In posistor relays ("tablets"), it is critically important to inspect yourself ceramic element. It should not have cracks, chips or signs of swelling. If the posistor has broken into pieces, further checking with a multimeter no longer makes sense - the element is clearly faulty and requires replacement. Also check the condition of the springs and moving parts in the induction relays: they should move freely and return to their original position under the influence of gravity (or a spring) without getting stuck.
Is it possible to restore a burnt relay?
Theoretically, you can try to restore an induction relay by cleaning the contacts with fine sandpaper and rinsing with alcohol. However, practice shows that such a measure gives only a temporary effect. The metal of the contacts has already burned out, and the problem will return in a short time. In addition, violation of factory calibration can lead to failure of the compressor itself, so replacing with a new unit is the only correct solution.
If a visual inspection does not reveal obvious defects, such as cracks or obvious carbon deposits, this does not guarantee the serviceability of the device. Electrical breakdown or breakage of the coil winding is not visually detected. This is where a multimeter comes to the rescue, which will allow you to look “inside” the electrical circuit.
Step-by-step instructions: how to test a relay with a multimeter
To carry out the test, set the multimeter to resistance measurement mode (indicated by the Ω icon), selecting a limit of 200 Ohms or testing mode with a sound signal. The test process depends on the type of relay you have, so it is important to first determine what kind of device you are dealing with. Let's look at the algorithm for both types.
For induction relays (with a coil), the test is performed as follows:
- 📏 Find the control coil terminals. Usually there are two. Attach the multimeter probes to these contacts.
- 🔊 The device should show a resistance in the range from 30 to 200 Ohms (the exact value depends on the model). If the resistance is infinitely high (one on the screen), the coil is broken. If zero - short circuit.
- ⚡ Check the moving core. In a horizontal position, the contacts of the starting winding must be open (resistance is infinite). If you turn the relay over (simulating switching on), the contacts should close and the multimeter will beep.
For positor relays (start-up protection "tablet") the algorithm is slightly different:
- 🌡️ Measure the resistance between the main ones contacts. At room temperature, the posistor has low resistance, usually from 3 to 50 Ohms.
- 🔥 Warm up the element. To fully test the posistor, you need to warm it up (for example, with a hairdryer), its resistance should increase sharply to several megaohms. At home, they are often limited to checking for a break in a cold state.
- 🛡️ Check the integrity of the thermal protection. If it is built into the case, ring its terminals. The resistance should be close to zero. The presence of resistance indicates that the protection has burned out.
☑️ Checklist for checking the relay
If during the test you found that the coil resistance is absent (break) or equal to zero (short circuit), or the contacts do not close/open mechanically, the relay is considered faulty. Such elements, as a rule, cannot be restored and require replacement with similar characteristics.
Table of typical resistance values and faults
For ease of diagnosis, we provide a summary table that will help interpret the readings of your measuring device. Remember that the values may vary slightly depending on the compressor manufacturer (Danfoss, Atlant, LG, Samsung) and the ambient temperature.
| Check type | Normal reading | Failure sign | Probable reason |
|---|---|---|---|
| Coil resistance (Induction) | 30 - 200 Ohm | ∞ (Infinity) or 0 Ohm | Open turns or interturn short circuit |
| Starting circuit contacts (Induction) | 0 Ohm (in working position) | ∞ (Do not close) | Burning of contacts, jamming of the core |
| Posistor (Cold condition) | 3 – 50 Ohm | ∞ (Infinity) | Destruction of the ceramic element, break |
| Thermal protection | 0 – 1 Ohm | ∞ (Infinity) | Bimetallic plate burnout |
Please note that the resistance of the windings of the compressor itself (between the contacts on the motor housing where the relay is placed) also matters. The total resistance of the starting and operating windings is usually 10-30 Ohms. If the multimeter shows a short circuit to the case or between the windings, the problem may not be in the relay, but in the motor itself.
Using the table allows you to quickly eliminate obviously non-working options. However, even if the readings are close to normal, but the refrigerator does not work, it is worth thinking about replacing the relay, since its parameters could be within the tolerance limits, but become insufficient for a confident start of the aging compressor.
Replacing a faulty element and frequent errors
If diagnostics have confirmed a faulty relay, it must be replaced. Selecting an analogue is a critical stage. You can’t buy the first relay you come across, even if it’s the right size. The key parameters are the engine power (in watts or horsepower), the type of compressor (low speed or high speed) and the type of refrigerant the system is designed to handle. This data is indicated on the compressor nameplate or on the body of the old relay.
The process of installing a new relay is simple: it is put on the compressor contacts until it stops and secured with a bracket or strip. Orientation is important: the relay body often has a marking UP or arrow indicating that side should face up. This is especially important for induction relays where operation is based on gravity. Installation “upside down” will result in the core not being able to move and startup will not occur.
Common mistakes made during repairs:
- 🚫 Ignoring orientation. As mentioned above, incorrect position of the relay makes its operation impossible.
- 🚫 An attempt to “revive” a burnt posistor. Ceramics cannot be glued or repaired, only replaced.
- 🚫 Closing the contacts directly. Some “craftsmen” advise connecting the wires directly, bypassing the relay. This is absolutely not allowed! The compressor will start, but after a few seconds it will burn out, since the starting winding will not turn off.
⚠️ Attention: Technical characteristics of compressors and requirements for starting fittings may vary depending on the model and year of manufacture. Always check the labeling of the new relay with the data on the nameplate of your refrigerator. Using an unsuitable relay can lead to overheating and fire.
After installing the new relay and assembling the protective casing, you can turn on the refrigerator. A successful start is characterized by a smooth hum of the motor and the absence of frequent clicks. If the motor hums but does not start, or immediately knocks out the circuit breaker, the problem should be looked for deeper - in the compressor itself or the wiring.
Conclusion and conclusions
Diagnostics of the refrigerator start-up relay is an accessible procedure that can be done by any home craftsman with a minimum set of tools. The ability ring the relay to use a multimeter allows you to quickly determine the cause of the breakdown and avoid unnecessary expenses on calling service. In most cases, replacing this inexpensive unit brings the refrigerator back to life, extending its service life by years.
However, if after replacing the relay the problem does not disappear, or you find that the resistance of the windings of the compressor itself does not correspond to the norm, further independent repairs may be dangerous and impractical. In such situations, it is better to contact professionals who have the equipment to evacuate the system and charge the refrigerant if the motor-compressor itself needs to be replaced.
Regularly keep the condenser on the back wall of the refrigerator clean and ensure good ventilation. Overheating is the main enemy of starting equipment, and keeping the equipment clean will significantly reduce the risk of relay failure in the future.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay?
Technically, it is possible to start a compressor without a starting relay, using a button to forcefully close the starting winding for 1-2 seconds, but doing this is extremely dangerous and is not recommended. Without thermal protection and automatic shutdown of the starting winding, the motor will burn out in a few seconds or minutes. Operating a refrigerator without a working relay is prohibited.
Why does the relay click, but the refrigerator does not turn on?
Clicks indicate that the thermal protection is activated, opening the circuit. This can happen for three reasons: the relay itself is faulty (the contacts are stuck or the posistor is burned out), the compressor is jammed (mechanical failure), or an interturn short circuit has occurred in the motor windings. Diagnostics should begin by checking the relay.
Where to find the markings for selecting an analogue relay?
Look for the markings on the body of the oldest relay (often it is erased or smoked) or on a metal tag (nameplate) on the compressor body. It shows the power (eg 1/4 HP, 1/3 HP) or watts (W) and the type of refrigerant. Based on these parameters, the store selects a compatible model.
How long does a starting relay last?
The average service life of a starting relay is 5-10 years, but it greatly depends on the quality of the electrical network and the frequency of voltage drops. Frequently turning the refrigerator on and off also reduces the life of the contacts. When unstable operation of the refrigerator occurs, the relay should be checked first.