A sudden stop in the operation of a refrigeration unit often takes you by surprise, especially when there are perishable products in the chamber. In most cases, the cause of the breakdown is the failure of the starting or thermal relay, which is responsible for starting and protecting the compressor. Protective relay This is a small but critical element of the electrical circuit, without which normal operation of the motor is impossible.
Symptoms of a malfunction usually appear clearly: compressor It may hum but not start, or it may turn on for a few seconds and immediately turn off with a characteristic click. Sometimes the engine is completely silent, although the indicators on the control panel are on. Understanding the operating principle of this unit will help you quickly determine whether the part needs to be replaced or whether the problem lies deeper.
Self-diagnosis requires a minimum set of tools and basic knowledge of electrical engineering. In this article we will analyze in detail the design of various types of relays, methods for checking them with a multimeter and visual inspection. Attention: any work on electrical components should be carried out only after completely disconnecting the device from the network.
Design and principle of operation of the starting relay
The start relay is an electromagnetic switch that briefly supplies voltage to the compressor start winding. As soon as the motor rotor reaches the required speed, the mechanism opens the circuit, leaving only the main winding to work. Start relay there are two main types: with a posistor (solid-state) and induction (with a moving core).
Induction models, often found in old refrigerators, operate due to the magnetic field of the coil. When current is applied, the core is retracted, closing the contacts of the starting winding. In modern models, posistor relays are more often used, where the role of a switch is played by a thermistor that changes its resistance when heated. Solid-state relays They are considered more reliable, since they have no moving mechanical parts.
⚠️ Attention: Never try to test the relay while the compressor is connected to the mains. Residual charge in capacitors or accidental contact with live parts can result in serious electrical injury.
Failure of this unit will result in the compressor not receiving a starting impulse. The engine hums, trying to move, but without turning on the starting winding there is not enough torque. After a few seconds, the thermal protection is triggered, and the unit goes silent until the next start attempt cycle.
Visual inspection and initial diagnosis
The first stage of diagnosis should always be a thorough external examination. Remove the back panel of the refrigerator, find the compressor and carefully remove the protective casing from the relay. Visual defective allows you to identify obvious signs of damage without using complex instruments.
Pay attention to the condition of the plastic case. If melting, cracks or traces of soot are visible on it, this is a sure sign of overheating or a short circuit inside. Also inspect the contacts: blackening or oxidation indicates a poor connection that could cause sparking.
- 🔍 Check the integrity of the wires going to the relay - they should not be chafed or melted.
- 👃 Smell the part - a strong smell of burnt plastic or insulation indicates an internal breakdown.
- 🔊 Shake the relay (if it is induction) - a knock inside may mean a breakdown of the mechanism or core.
If there is no external damage, proceed to a deeper check. However, even with an ideal appearance, the internal electronics could fail. Posistor in solid-state relays it often burns out unnoticed by the eye, changing its properties.
Instrumental testing with a multimeter
For accurate diagnostics you will need a multimeter (tester). Switch the device to resistance measurement mode (Ohms). This method allows you to determine the integrity of the windings and the condition of the contacts with high accuracy.
First check the thermal relay (overload protection). In a cold state, its contacts should be closed, and the device will show zero or close to zero resistance. If the multimeter shows one (infinity), then the circuit is broken and the part must be replaced. Thermal relay is a fuse that should conduct current in normal mode.
Then proceed to check the starting part. For induction relays, the resistance between the contacts of the main and starting windings should be minimal. In the case of posistor relays, the resistance of the posistor itself at room temperature is usually 3–50 Ohms. If the device shows a break or the resistance is very different from the nominal value, the element is faulty.
☑️ Test algorithm with a multimeter
Therefore, if in doubt, it is better to replace the part with a new one, since its cost is low. Multimeter gives only indirect confirmation of serviceability, but not guarantees 100% performance under load.
Table of typical faults and symptoms
For ease of data systematization, we have collected the main signs of breakdowns in a single table. This will help you quickly compare the behavior of your refrigerator with a specific malfunction.
| Symptom | Probable cause | Check method | Solution |
|---|---|---|---|
| Humming and clicking | Faulty starting relay | Connection with a multimeter | Replacement of the relay |
| Compressor silence | Open thermal relay | Visual inspection, continuity | Replacement of protection |
| Short-term start-up | Sticking of contacts | Visual inspection of contacts | Cleaning or replacement |
| Burning smell | Overheating of wiring or relay | Organoleptic (smell) | Replacing the unit and checking the wiring |
This table covers the most common scenarios. However, if after replacing the relay the problem persists, the compressor itself may be faulty or there are problems with the wiring of the refrigerator. Diagnostics must be comprehensive.
Replacing the relay: step-by-step instructions
If the check confirms a malfunction, the part must be replaced. The replacement process is simple, but requires care. Make sure that you purchase a similar model, since relays from different manufacturers may differ in design and electrical characteristics.
⚠️ Attention: The technical characteristics of the relay (operation current, connection type) must strictly correspond to the model of your compressor. Installing an unsuitable relay may result in burning out the motor windings.
First remove the old relay by disconnecting the wires. Be careful, the terminals may be tight. Install the new part by sliding it onto the compressor contacts until you hear a characteristic click. Connect the wires in the same order in which they were connected previously.
- 🛠️ Carefully place the relay on the compressor rod, avoiding distortions.
- 🔌 Connect the wires, observing the polarity (if indicated).
- 🔧 Fix the casing and return the refrigerator to a vertical position.
- ⏳ Wait 15-20 minutes before turning on so that the refrigerant stabilizes.
After assembly, turn on the refrigerator and listen to the operation of the motor. It should start smoothly, without buzzing or clicking. If everything went well, after some time the temperature in the chamber will begin to decrease.
What to do if the new relay also does not work?
If, after installing a new, known-to-be-good relay, the compressor does not start or the machine immediately knocks out, the problem may be in the compressor itself (jamming, broken winding) or in the wiring. In this case, you need to call a specialist for a deeper diagnosis.
Frequent errors during diagnostics and repair
Beginners often make mistakes that can aggravate the situation. One of the most common is an attempt to “revive” an old relay by tapping or cleaning the contacts. In modern sealed enclosures this is useless and dangerous.
Another mistake is ignoring the compressor condition. If a relay burns out, this is often a consequence, not a cause. For example, a difficult start of the compressor due to low voltage in the network or problems with the refrigerant could overload the relay. Cause of overload must be eliminated, otherwise the new relay will also burn out.
Do not forget about safety precautions. Working with electrical appliances requires sobriety and care. If you are not confident in your abilities, it is better to entrust the repair to professionals. Safety saving on calling a technician is always more important.
Is it possible to temporarily start a refrigerator without a relay?
Technically, you can start an asynchronous motor by applying voltage to the starting winding manually, but doing this is strictly prohibited in domestic conditions. This requires special equipment and skills, and the risk of burning the compressor or starting a fire is extremely high.
Why does the relay heat up during operation?
Slight heating is acceptable, but if the relay gets hot, this indicates poor contact, incorrect selection of the part or overload of the compressor. Long-term operation in this mode will lead to melting of the housing and a fire.
How often do you need to change the starting relay?
The relay does not have a specific service life. It changes only upon failure. High-quality parts last 10-15 years or more, but power surges can shorten this period.
Does the brand of refrigerator affect the choice of relay?
Yes, it does indirectly. It is important to select a relay for a specific compressor model (Danfoss, Secop, LG, Samsung), and not just for the refrigerator brand. Compressors of different brands can be installed in the same refrigerators.