Sudden stoppage of the compressor or characteristic clicks when trying to start the refrigerator often indicate a faulty start relay. This small but critical element is responsible for supplying voltage to the motor windings at the moment of start. If you notice that the motor is humming, but does not start, or, conversely, is silent, although power is supplied, the first thing you should suspect is this particular unit.
Relay diagnostics is a procedure that is accessible even to a layman with basic tools and an understanding of the principles of electrical operation. Start relay necessary to turn on the starting winding of the compressor, allowing it overcome the inertia of rest. Ignoring the symptoms of a breakdown can lead to failure of the compressor itself, the repair or replacement of which is much more expensive.
In this article we will analyze in detail the algorithm for identifying a defect, consider the types of relays and methods for testing them. You will learn how to distinguish a burnt part from a serviceable one and whether it is worth trying to revive the old element or is it better to immediately purchase a new one. Visual inspection and testing with a multimeter are two pillars on which high-quality diagnostics are based.
Symptoms of a faulty starting relay
The first sign that should alert the owner of the equipment is the uncharacteristic behavior of the compressor when turned on. Often the refrigerator will make a loud click, followed by a hum that lasts a few seconds, and then another click followed by silence. This is a classic scenario when starting winding does not receive the necessary impulse to start, and the thermal relay turns off the motor to avoid overheating.
In some cases, the motor may start, but work intermittently or get excessively hot in the lower part of the housing. If you notice that the refrigerator has stopped freezing, but the back grill remains cold, this may indicate that the compressor is not working at all. The smell of burning or melted plastic in the compressor area is also an alarm bell.
- 🔊 The compressor hums for 3-5 seconds, then a click is heard and silence sets in.
- 🔥 The relay or compressor housing gets very hot when trying to start.
- ⚡ Appearance smell of burnt wiring or plastic in the compressor niche.
- ❄️ The refrigerator does not gain temperature, although the indicators are on.
⚠️ Attention: If after clicking the compressor continues to hum and does not turn off for more than 10 seconds, immediately unplug the cord from the outlet. Long-term operation in the “start” mode without rotation of the rotor is guaranteed to damage the engine.
Design and principle of operation of the relay
To effectively carry out diagnostics, you need to understand how this element works. In modern refrigerators, two types of devices are most often found: posistor (PTC) and induction. A posistor relay is a tablet made of a special material, which, when current is applied, heats up and sharply increases its resistance, opening the starting winding circuit.
Induction relays operate on the principle of an electromagnet. When current passes through the coil, a magnetic field is created, which draws in the core and closes the contacts of the starting winding. When the engine speed increases, the current drops, the spring returns the core, and the circuit opens. Contact group in such devices it is subject to oxidation and burning.
Inside the case there is also often built-in thermal relay protection, which opens the circuit when the compressor windings become critically heated. It can be made in the form of a bimetallic plate. Understanding the difference between the starting and thermal element is important, since sometimes only one of them fails, although usually the entire assembly is replaced.
Visual inspection and preparation for diagnostics
Before picking up a multimeter, it is necessary to conduct a thorough external inspection. Any work with electrical appliances begins with a complete disconnection from the network. Remove the back cover of the refrigerator, gain access to the compressor and carefully remove the plastic casing covering the relay and capacitor.
Disconnect the relay connector from the compressor contacts. Usually it is simply removed from the pins, sometimes secured with a metal bracket. Carefully inspect the case for cracks, blackening or signs of melting. If the plastic turns black, this is a sure sign that a breakdown or short circuit has occurred inside.
Shake the relay near your ear. If something rattles inside, it means that the contact group or the posistor element has collapsed. For induction relays, this is a normal sign of a malfunction, since the core must be firmly fixed. Also check the condition of the wires going to the relay: they should not be brittle or have damaged insulation.
☑️ Initial inspection of the relay
Checking the relay with a multimeter
The most accurate way to determine operability is to test the contacts with a multimeter. Switch the device to resistance measurement mode (Ohms). For posistor relays, the resistance of a working element is usually from 10 to 100 Ohms, the exact values depend on the model and temperature.
If the multimeter shows one (infinity), then the circuit is broken and the posistor has burned out. If it shows zero, a short circuit has occurred. For induction relays, the integrity of the coil is checked: the resistance should be low, but not zero. The contacts are also checked for short circuits with each other in a quiet state.
It is important to check not only the starting part, but also the thermal relay, if it is built into one housing. Ring the contacts of the thermal relay: in a cold state they should ring (resistance is close to zero). If the multimeter shows a break, the thermal protection is faulty and requires replacement.
| Relay type | Normal resistance | Fault symptom | Action |
|---|---|---|---|
| Posistor (PTC) | 10 - 100 Ohm | Infinity or 0 Ohm | Replacement |
| Induction (Coil) | Low (up to 50 Ohm) | Open circuit | Replacement |
| Thermal (Bimetal) | 0 Ohm (closed) | Open in cold state | Replacement |
| Contacts (Induction) | 0 Ohm (at rest) | High resistance | Cleaning or replacement |
Direct voltage application method (Lamp test)
There is a more complex, but clear method of verification - applying voltage directly. To do this, you will need a piece of wire with a plug and a regular incandescent lamp (power 60-100 W), which will serve as a load and indicator. This method allows you to check whether the relay contacts close when current is applied.
Assemble a simple circuit: the phase from the plug goes to one relay input, the zero goes to the other input (or to a common contact, depending on the circuit). The lamp is connected in series with the starting winding. When power is applied, a working posistor relay should close the circuit, the lamp will light up, and after a few seconds, when the posistor heats up, the circuit will open and the lamp will go out.
For induction relays, the lamp should light up at the moment voltage is applied and go out if the relay properly opens the contacts after operation. However, this method requires caution: you are working with a mains voltage of 220V. Do not perform this test if you are not confident in your skills in working with high voltage, the risk of electric shock is real.
⚠️ Attention: When testing under voltage, never touch the metal parts of the circuit with your hands. Use insulated clamps and dielectric gloves. The lamp is required to limit the current; direct connection without load can lead to an explosion of the faulty element.
Replacement and selection of a new element
If the diagnostics showed a malfunction, the relay must be replaced. Repairing the internal structure of a posistor or sealing an induction relay at home is impossible and impractical. The new element must strictly correspond to the markings of the old one. Main parameters: compressor type, engine power and mounting hole diameter.
Remove the old relay and look at its markings. Often it is applied to the side edge or top cover. Look for codes like R6, RT, PTC and numbers indicating the diameter of the compressor shaft (for example, 1/4" or 1/5"). There are no universal relays; a device selected “by eye” may not be suitable for the operating current.
Installation of a new relay is carried out in the reverse order of removal. Make sure that the contacts fit tightly on the pins of the compressor, and that the relay itself is locked in the correct position (usually the arrow UP should point up). After assembly, turn on the refrigerator and listen: the start-up should be quiet, without long hums.
Is it possible to repair a relay if it has simply oxidized?
Theoretically, if we are talking about an induction relay with burnt contacts, they can be cleaned with fine sandpaper. However, this is a temporary measure. The contact surface is broken, and after a short time the sparking will resume with renewed vigor. For posistor relays, cleaning is useless, since the problem is inside the crystal.
Why does a new relay burn out immediately after installation?
This may indicate a more serious problem, for example, an interturn short circuit in the compressor windings or jamming of the piston group. In this case, the motor draws too much current, which melts the relay contacts. Also, the cause may be incorrect installation (wrong side).
Where to find the markings on the relay?
The markings are usually applied with black paint on the side plastic surface or on the metal cover (if there is one). Look for manufacturer's inscriptions (Danfoss, Secop, Start) and alphanumeric codes. If the inscription is erased, look for the catalog number on the plastic itself.
Does the room temperature affect the operation of the relay?
Yes, it does. PTC relays are temperature sensitive. In a very cold room (below +10°C), the posistor cooling time increases, which can lead to an increase in the pause between attempts to start the compressor. In hot weather, the relay may operate faster.