A sudden stop of the compressor or its inability to start often confuses the owner of household appliances. Instead of panic and urgently calling a technician, you should pay attention to a small but critical element - the start relay. It is this unit that is responsible for supplying voltage to the motor windings at the time of start, and its failure is one of the most common causes of failure of older models of refrigerators.
Diagnostics of this component does not require deep knowledge in electronics, but does imply compliance with safety precautions when working with electricity. Checking the relay takes only a few minutes if you know where the contacts are and how to use the measuring instrument correctly device. In this article we will analyze all the nuances of diagnostics, types of devices and methods of testing them.
Before starting disassembly, it is necessary to completely turn off the power to the refrigerator. Unplug the power cord and gain access to the compressor, which is usually located at the lower rear of the unit. Only after this can you remove the protective casing and begin to remove the trigger mechanism.
Design and principle of operation of the trigger mechanism
The starting relay is an electromechanical switch that closes the circuit of the starting winding of the electric motor only at the moment of starting. As soon as the compressor rotor reaches the required speed, the device opens the contacts, leaving only the working winding running. In older models, electromagnetic or posistor systems are most often found.
Electromagnetic relays operate by current flowing through a coil, which draws in the core and closes the contacts. The posistor options use a special ceramic element, which is heated by current and sharply increases its resistance, breaking the circuit. Understanding exactly which type of relay is installed in your refrigerator is important for correct diagnosis.
A thermal protection relay can also be located inside the case, which opens the circuit when the compressor overheats. Often these two elements are combined into one block, but can be physically separated. Thermal protection triggered if the current in the circuit exceeds the norm or the temperature of the motor housing becomes critical.
What is the difference between an induction and a posistor relay?
Induction (electromagnetic) relays have a moving core and contacts that can stick or burn. PTCs do not have moving parts inside the switch itself; they work by changing the resistance of the crystal when heated. PTC resistors are considered more reliable, but are sensitive to shock.
Visual inspection and initial diagnosis
The first stage of testing should always be a thorough external examination. Remove the relay from its seat on the compressor, having first photographed or memorized the wiring diagram. The device body should not have cracks, traces of melting or burning.
Shake the relay next to your ear. If a characteristic ringing or knocking sound is heard inside, this is a sure sign that the contacts or core have come off. In this condition, the device can no longer be repaired and requires replacement. Also pay attention to the condition of the contact groups - they must be clean, without black soot.
⚠️ Attention: If you see traces of soot or smell burning, do not under any circumstances try to clean the contacts with sandpaper. This is a temporary measure that may result in a short circuit and fire.
Inspect the wires leading to the relay. The insulation must not be damaged, and the terminals must fit tightly on the contacts. A loose contact can cause sparking and heating, which simulates a breakdown of the relay itself. Primary diagnostics allows you to eliminate up to 30% of problems without using tools.
Necessary tools for checking
For high-quality diagnostics, you will need a minimum set of tools that any home craftsman will have. The main device will be a multimeter (tester) capable of measuring resistance and checking the integrity of the circuit. Without it, an accurate check is impossible.
You may also need pliers to remove the terminals, a screwdriver to remove the compressor protective casing, and possibly fine sandpaper to clean the contacts of the compressor itself if they have oxidized. Don't forget to prepare a container for testing functionality if you decide to test the relay under voltage.
☑️ Diagnostic tools
Make sure that the multimeter is working and its batteries are not discharged. Switch the device to resistance measurement mode (Ohm) or dialing mode with a sound signal. This will allow you to quickly determine the presence of an open circuit or short circuit inside the device.
Step-by-step instructions: how to test a relay with a multimeter
The testing process depends on the type of device, but the general algorithm is similar. First you need to determine the purpose of the contacts. Usually there are three or four of them: two for connecting to the compressor (start and operation) and two for connecting to the network (phase and zero). The circuit is often marked on the body or cover of the relay.
Take a multimeter and install the probes on the contacts responsible for the starting winding. In the initial position (the relay is not inverted), the resistance should be infinite (one on the screen). Now carefully turn the relay 180 degrees (simulating turning on the compressor).
If the relay is working, you should hear a click, and the device will show a resistance close to zero (or several ohms). This means that the contacts have closed. If there is no resistance or it is constantly infinite, the device is faulty. Testing with a multimeter is the most reliable method.
For thermal relays, the test is similar: the resistance should be zero in both positions, since they are normally closed. Opening occurs only when heated or strong shaking (depending on the design). If the thermal relay “rings” as open, it has burned out.
Table of typical faults and symptoms
To quickly navigate the symptoms, use the following table. It will help to compare the behavior of the refrigerator with the possible cause of the breakdown of the relay or adjacent components.
| Symptom | Probable cause | Action |
|---|---|---|
| The compressor hums, but does not start | The piston group is jammed or the starting relay is burned out | Check the relay, try to start the compressor directly |
| Clicks every few minutes | Thermal protection is triggered due to overheating | Check the thermal relay and condenser ventilation |
| The refrigerator does not turn on at all | Open circuit in the relay or thermostat | Ring the compressor power circuit |
| The machine in the panel knocks out | Short short circuit in the windings or relay | Disconnect immediately, check the resistance of the windings |
It is important to understand that the symptoms may overlap. For example, the hum of a compressor without starting can indicate not only a broken relay, but also that it itself is jammed. Therefore, the diagnostics must be comprehensive. compressor jammed. Therefore, diagnosis must be comprehensive.
Voltage test and safety measures
If the multimeter shows that the contacts are working properly, but the refrigerator does not work, you can carry out a voltage test. This method requires extreme caution, as it involves working with a mains voltage of 220 Volts.
Connect the relay to the compressor, and connect the wires from the power cord to the input terminals of the relay. Plug the cord into the outlet for a split second. If the relay is good, you will hear a click and the compressor should start. If you hear a loud crash or knock out plugs, stop immediately.
⚠️ Attention: Never hold a live relay in your hands without insulation. The risk of electric shock during such a test is maximum. Use dielectric gloves or insulated tools.
An alternative safe method is to use a light bulb. Connect an incandescent lamp with a power of 100-150 W in series to the relay power circuit. If, when turned on, the lamp lights up at full intensity and goes out after a click, the system is working. If it lights up brightly, there is a short circuit. If it doesn’t light up, there’s a break.
Replacing and selecting a new relay
If the diagnostics confirmed a malfunction, the relay must be replaced. It makes no sense to repair modern sealed enclosures, since their tightness and reliability are compromised. Buying a new device is the only right decision.
When choosing an analogue, pay attention not only to the appearance, but also to the markings. The key parameters are the compressor power (e.g. 1/4 HP, 1/3 HP) and the type of refrigerant (R12, R134a, R600a). An incorrectly selected relay can quickly burn out or not start the engine.
Install the new relay onto the compressor fitting until it clicks or stops. Connect the wires according to the diagram, which is usually located on the cover or in the instructions. Make sure that the orientation of the relay corresponds to the marking (the UP arrow should face up).
Is it possible to use a relay from another refrigerator?
Yes, if the main parameters match: voltage (220V), frequency (50Hz), compressor power and type of freon. Visual similarity does not always guarantee compatibility, so check the manufacturer codes.
Why does the relay burn out again after a short time?
Repeated failure often indicates a problem not in the relay itself, but in the compressor. If the engine is “heavy” (tight piston stroke), the starting currents exceed the norm, and the relay burns out. Also, the reason may be low voltage in the network or a malfunction of the capacitor (if there is one in the circuit).
Where can you find the power marking on the relay?
Usually the power is indicated on the side face or end of the case in the form of a fraction (for example, 1/5, 1/4, 1/3) or in Watts. Sometimes a letter code is used, the decoding of which is in the catalogs of spare parts manufacturers.
How much does it cost to replace a relay by a master?
The cost consists of the price of the spare part (usually from 500 to 1500 rubles) and the work of the master. In the regions, the price of the service can vary from 1000 to 2500 rubles. Self-replacement saves the cost of work, but requires tools.
Is it possible to solder the relay contacts?
Theoretically, it is possible if the case allows disassembly, but practice shows that such a measure is temporary. The factory calibration of the trip current is violated and the risk of fire increases. It is better to buy a new original or universal relay.