Sudden stop compressor or a characteristic click followed by silence are the first signals that there is a failure in the electrical circuit of your refrigerator. Often the cause of such symptoms is refrigerator relaya small but critical device responsible for starting and protecting the motor. Understanding the principle of its operation is necessary for every owner of household appliances, since it is this component that most often fails due to power surges or natural wear.
If you ignore the signs of malfunction, you may encounter more serious consequences, including overheating of the motor windings and expensive compressor repairs. The relay controls the supply of current to the starting winding at the time of starting, and then turns it off, allowing the motor to operate normally. In the article we will analyze in detail how starting and thermal relays are constructed, how they differ and how to independently determine that the part requires replacement.
Diagnostics of this part does not require complex equipment, but requires care and compliance with safety precautions. Knowing the main symptoms of a breakdown, you can quickly determine whether the problem lies in the electronics, wiring or the compressor itself. Below we will look at all aspects of the functioning of this unit so that you can carry out repairs with confidence.
The principle of operation and types of relays in the refrigerator
The main task of the starting relay is to briefly supply voltage to the starting winding of the compressor motor. When the refrigerator is turned on, the motor rotor is motionless, and to spin it up, a significant torque is required, which is provided by the starting winding. As soon as the engine reaches the required speed (usually about 75% of the rated speed), the relay should instantly break the starting winding circuit, leaving power only on the working winding.
There are two main types of devices used in modern and classical technology: electromagnetic and posistor. Electromagnetic relays, often called current relays, use a coil in series with the operating winding. At a high starting current, the magnetic field of the coil draws in the core, closing the contacts of the starting winding. Posistor relay works based on the properties of a semiconductor element (posistor), which, when heated by current, sharply increases its resistance, actually opening the circuit.
What is the difference between a posistor and an electromagnetic relay?
Electromagnetic relays make an audible click every time they start and are more position sensitive (they only work in a certain orientation). The posistor ones operate more silently, are less sensitive to vibrations, but require time (about 3-5 minutes) to cool down before restarting after a power outage.
A thermal protection relay often operates in parallel with the starting mechanism. It is a bimetallic plate that bends when heated. If the current in the circuit exceeds the permissible limits (for example, when the compressor is jammed), the plate heats up, opens the contacts and de-energizes the engine, preventing its combustion. After cooling, the contacts close again, trying to start the motor again.
Typical symptoms of a faulty starting device
You can determine that the refrigerator relay has failed by a number of characteristic signs that appear immediately after the equipment is turned on to the network. The most obvious symptom is when the compressor hums, trying to start, but after a few seconds there is a clicking sound and the motor stops. After some time (usually 3-5 minutes, until the thermal protection cools down), the cycle repeats. This phenomenon is called “cyclic startup.”
Another sign may be the complete absence of the refrigerator’s response to turning on, if the contacts inside the relay have oxidized or burned so much that the circuit does not close at all. In some cases, a faulty relay may not open the starting winding, which leads to an overload of the engine and constant operation of the refrigerator at high speeds, accompanied by a strong hum.
- 🔊 The compressor makes a loud click, hums for 2-3 seconds and turns off.
- 🔥 The relay housing or the compressor itself becomes unnaturally hot to the touch.
- 🚫 The refrigerator does not freeze, although the power indicators are on.
- ⚡ When connected to the network, it knocks out circuit breakers or plugs in the panel.
It is important to distinguish between a relay failure and a malfunction of the compressor itself. If after replacing the relay the symptoms persist, the problem most likely lies in an interturn short circuit of the motor windings or mechanical jamming of the piston group. Diagnostics should be carried out sequentially to avoid wasting money on spare parts.
Visual inspection and initial diagnostics
Before proceeding with complex measurements with a multimeter, it is necessary to conduct a thorough visual inspection. To do this, the refrigerator is disconnected from the power supply and the rear protective panel at the bottom of the case, where the compressor is located, is removed. The relay is usually placed directly on the contact group of the compressor or secured next to it.
The first thing you need to pay attention to is the appearance of the part’s body. If you see melted plastic, blackening, or smell a burning smell, this is a sure sign that there is a short circuit or overheating inside. It is also worth checking the condition of the contacts: they must be clean, free of oxides and soot.
⚠️ Attention! Before removing the relay, be sure to unplug the refrigerator. Even after switching off, there may be a residual charge in the capacitors, so do not touch live parts with bare hands without first discharging them.
Remove the relay from the compressor pins. This may require carefully removing the retaining bracket or bar. Pay attention to the markings: the arrows on the housing indicate the correct installation position ("UP" or "DOWN"). Incorrect installation of a new relay can lead to its immediate failure, since mechanical contacts depend on gravity.
If no visual defects are detected, we proceed to “listening”. Shake the relay near your ear. If you hear a ringing or knocking sound inside of parts (contacts or springs) that have fallen off, the part is clearly faulty and requires replacement. A working relay should not make any sounds when shaken.
Checking a relay with a multimeter: step-by-step instructions
For accurate diagnostics, you will need a multimeter switched to the resistance (Ohm) or continuity measurement mode. This stage allows you to determine the integrity of internal circuits and the operation of contacts. First, let's check the thermal relay (if it is separate or integrated into the overall circuit).
Attach the multimeter probes to the input and output contacts of the thermal relay. The device should show zero or close to zero resistance, which indicates the integrity of the circuit. If the screen displays one or infinity, it means that the bimetallic plate has burned out and does not conduct current - the relay is faulty.
☑️ Checking the relay with a multimeter
Next we check the start relay. Depending on the design, the wiring diagram may differ, but the general principle is this: the resistance between the contacts responsible for the starting winding should be minimal at rest (for some types) or change when voltage is applied (for electromagnetic ones). For posistor relays, the resistance between the contacts should be stable, but when voltage is applied (which is difficult to check at home without a stand), it should increase.
The most reliable way to test an electromagnetic relay is to check the contacts are closed in a vertical position. In a vertical position (as on a compressor), the contacts must close (resistance 0