A sudden stop of the refrigerator or, conversely, its continuous operation without cooling is always stressful for the owners. Most often, the cause of failure is not the compressor itself, but its starting system, in particular start-up protection relay. This small component is responsible for supplying voltage to the motor windings and protecting against overheating, so its serviceability is critical.
Before calling a technician or buying expensive spare parts, it makes sense to carry out initial diagnostics yourself. To do this, you only need a Phillips screwdriver and multimeter (tester). The verification procedure takes a little time, but allows you to accurately determine whether the unit needs to be replaced or the problem lies deeper.
In this article we will analyze in detail the relay device, the symptoms of its failure and the method of contact testing. You will learn to distinguish between types of relays, correctly interpret instrument readings and safely carry out work with the electrical equipment of a refrigeration unit.
The design and principle of operation of a starting relay
The starting relay is an electromechanical switch that controls the supply of current to the starting winding of the compressor electric motor. At the moment of starting, the motor requires a powerful impulse to move the rotor from its place, after which there is no need for a starting winding. Relays automatically opens the starting winding circuit when the engine reaches the required speed.
There are two main types of such devices: posistor and induction. PTC models, which are more often found in modern refrigerators Indesit or Atlant, use a heat-sensitive element (posistor), the resistance of which increases sharply when heated, breaking the circuit. Induction relays operate due to the electromagnetic field created by the current in the main winding.
Protections are often built in parallel with the trigger mechanism. It is a bimetallic plate that opens contacts when the permissible temperature or current is exceeded. This prevents the compressor windings from burning out when the network is jammed or overloaded. If this element fails, the compressor may not start at all or operate in short cycles. thermal relay protection. It is a bimetallic plate that opens contacts when the permissible temperature or current is exceeded. This prevents the compressor windings from burning out when the network is jammed or overloaded. If this element fails, the compressor may not start at all or may operate in short cycles.
⚠️ Attention: Before starting any work on dismantling the relay, be sure to disconnect the refrigerator from the power supply! Even after switching off, residual voltage may remain in the circuits, and careless handling of capacitors or contacts under load is dangerous.
Visual diagnostics and signs of malfunction
Before picking up measuring instruments, it is worth conducting an external inspection of the unit. Often the nature of the damage is visible to the naked eye. Remove the back cover of the compressor (if there is one) and carefully remove the relay from the compressor contacts. Usually it is attached with latches or simply put on three pins.
Inspect the case for melting, cracks or blackening. If carbon deposits are visible inside the housing or a burning smell is felt, then contact group most likely it is broken. Also pay attention to the condition of the contacts: oxidation or corrosion may prevent the normal flow of current.
Symptoms indicating the need to check the relay with a multimeter are usually the following:
- 🔊 The compressor hums for 5-10 seconds, then there is a click and it goes silent (does not start).
- ❄️ The refrigerator works constantly, but the temperature in the chambers does not drop below +10°C.
- 💡 When starting, a loud click is heard, after which the circuit breakers in the panel immediately knock out.
- 🔥 The compressor housing or the relay itself becomes very hot in the lower part of the refrigerator.
If no visual defects are found, we proceed to instrumental diagnostics. To do this, you will need a multimeter switched to resistance (Ohm) or continuity measurement mode.
Preparation for testing and safety precautions
To work correctly with the multimeter, you must correctly configure the device. Switch the knob to the resistance measurement sector, selecting the 200 Ohm limit or the audio test mode. Before starting measurements, make sure that the probes are in good condition: connect them to each other - the device should show zero or make a squeak.
The relay removed from the compressor must be cleaned of dust and dirt. If there is a slight coating on the contacts, it can be carefully cleaned with fine sandpaper, but try not to damage the metal itself. It is important to understand that posistor relays cannot be checked “on weight” immediately after work - they need to cool for at least 15-20 minutes, otherwise the readings will be incorrect.
When working with induction relays, be careful with moving parts. Inside such devices there is a spring-loaded core and contacts that can jump out if the case is opened carelessly. If the relay is non-separable and has damage to the case, it is better to replace it immediately, since restoring the tightness is impossible.
Step-by-step instructions: how to test a relay with a multimeter
The testing process depends on the type of relay, but the general algorithm of actions is similar. Let's consider checking the most common option - a posistor relay with three contacts. There are usually markings on the case, but if there are none, be guided by the location of the pins relative to the compressor.
Take a multimeter and attach the probes to the contacts. You need to check the circuit between the power contact (common) and the start winding contact. When cold, the posistor should have low resistance (usually from 3 to 50 Ohms, depending on the model). If the device shows infinity (one in the most significant digit or OL), it means that the posistor has burned out.
Next, we check the thermal protection relay. It is connected in series with the main winding. Ring the contacts going to the main winding of the compressor. The resistance should be close to zero (0.1–1 Ohm). If the multimeter shows an open circuit, it means that the thermal protection has tripped and has not returned to its original state, or it has burned out.
☑️ Checklist for checking the relay
For induction The relay technique is slightly different. Here it is important to check the ease of movement of the core and the condition of the contacts. The inductor resistance should also be low. If the core is stuck in the upper position, the starting winding circuit will not open, which will lead to motor burnout.
| Relay type | Normal resistance (cold) | Malfunction symptom | Action |
|---|---|---|---|
| Posistor | 3 – 50 Ohm | Infinity (break) | Relay replacement |
| Thermal protection | 0 – 1 Ohm | Infinity (break) | Replacement of relay |
| Induction | 10 - 30 Ohm (coil) | Stuck core | Replacement or cleaning |
| Contact | 0 Ohm (closed) | High resistance | Cleaning/Replacement |
⚠️ Attention: Do not attempt to test the relay connected to the compressor without removing it from the contacts. In this case, you will be measuring the resistance of the windings of the motor itself, which will give false results. The relay must be completely disconnected.
Analysis of results and search for hidden defects
After receiving digital values, it is important to interpret them correctly. If the resistance of the posistor is normal, but the refrigerator does not start, the problem may be “sticking” of the contacts. Sometimes when testing there is a circuit, but under load the contact disappears. In such cases, it is recommended to lightly tap the relay body on the table (carefully!) and repeat the measurements.
Pay special attention to checking for short circuits. Apply one multimeter probe to any relay contact, and the second to the metal case or frame. The device should not show any resistance (there should be an open circuit). If there is conductivity, then the internal insulation is broken, and operate such a device strictly prohibited.
In some cases, the relay may be in working order, but not suitable for a specific compressor. Different motor models require different operating currents. Installing a relay with inappropriate characteristics (for example, from a refrigerator of lower power) will lead to the fact that it will burn out immediately after switching on or will not be able to start the motor.
Why does a new relay burn out?
If you installed a new relay, and it burned out after a few seconds of operation, the cause may be a malfunction of the compressor itself. An interturn short circuit of the motor windings creates a starting current that exceeds the relay rating, which leads to its instantaneous failure. Check the compressor windings before reinstallation.
Replacing the relay and final recommendations
If diagnostics with a multimeter showed a malfunction, the relay must be replaced. When purchasing a new part, be guided not only by the external similarity, but also by the markings. The part code is usually stamped on the case or indicated in the technical documentation of the refrigerator (for example, PTM-11-9 or R6).
Installation is carried out in the reverse order of removal. Align the holes in the relay with the compressor contacts and press firmly until a characteristic click or stop. Make sure that the relay sits smoothly and is not skewed. After connecting, check the operation of the unit: the compressor should start, work and turn off when the set temperature is reached.
If after replacing the relay the situation has not changed (the compressor hums and clicks), the problem may be in the engine itself or in the wiring. In this case, independent repair becomes difficult and requires a qualified electrician.
Is it possible to temporarily start a refrigerator without a relay?
Technically, you can start the compressor directly by closing the contacts of the starting winding manually or through a button, but doing this is extremely dangerous and is not recommended Without thermal protection, the compressor. may burn out in a few minutes if jammed, and the absence of automatic shutdown of the starting winding will lead to overheating and fire. Use this method only for short-term diagnostics by an experienced technician.
Why does the relay heat up during operation?
Slight heating of the relay body (up to 40-50 degrees) is normal, as it passes through the posistor. current. However, if the housing becomes so hot that it is impossible to touch it, or a plastic smell appears, this indicates a poor contact, an incorrectly selected relay, or a compressor malfunction that creates an overload.
How to distinguish a relay for No Frost from a regular one?
Visually they can be identical. The main difference lies in the electrical characteristics indicated on the page. marking. For No Frost systems, relays with slightly different posistor cooling time or response current are often used. Always check the part code (Part Number) with the refrigerator manufacturer's catalog.
What to do if the relay has 4 contacts, and the compressor has 3?
The fourth contact is often an additional terminal for the capacitor or simply a structural element of the housing, not involved in the operation of this model. However, before ignoring it, find the connection diagram for your specific refrigerator model. Incorrect connection can lead to a short circuit.