If your refrigerator suddenly stops freezing, and only a quiet hum or a characteristic click followed by silence is heard from the engine compartment, the problem most likely lies in the compressor starting system. In such a situation, the first suspect becomes start-up protection relay, which is responsible for supplying voltage to the motor windings and protecting it from overloads. This compact device is a key element of the electrical circuit, and its failure makes it impossible for the entire unit to operate normally.
Before calling a technician or buying a new part, it is necessary to carry out an initial diagnosis to make sure that it is advisable to replace this particular component. Often, users mistakenly blame the compressor itself, although the cost of the relay is disproportionately lower, and replacement can be done independently if you have basic skills and tools. In this article, we will analyze in detail the design of the mechanism, methods for checking it with a multimeter and visual inspection, so that you can accurately determine the cause of the breakdown.
It is important to understand that ignoring the symptoms of a malfunction can lead to more serious consequences, including overheating of the electric motor windings. Start-protective relay not just starts the motor, but also turns off the starting winding after dialing rpm, and also breaks the circuit with a critical increase in current. If this process is disrupted, the compressor may run idle or constantly try to start, which will quickly disable it.
Principle of operation and structure of the mechanism
To understand how to check the serviceability of a part, you need to understand its internal structure. The start-up relay is an electromechanical switch that responds to the amount of current flowing through the compressor windings. Inside the case there are two main groups of contacts: starting and working, as well as a sensitive element that opens the circuit in case of overload. In modern models, most often there are devices with a posistor (solid-state) or an electromagnetic principle of operation.
Electromagnetic relay they work by changing the magnetic field in the coil. At the moment of starting, the current is high, the core is drawn in and closes the contacts of the starting winding. When the engine picks up speed, the current drops, the core drops under the influence of gravity or a spring, opening the starting circuit. Thermal protection in such models it is represented by a bimetallic plate that bends when heated and opens the contacts if the compressor overheats or the current exceeds the norm.
In devices with posistor (PTC relay), the role of a switch is performed by a ceramic element, the resistance of which increases sharply when heated. When voltage is applied, the posistor is cold and passes current to the starting winding. Heating up from the passing current, it becomes a dielectric, essentially turning off the starting winding. After cooling (usually 3-5 minutes), the resistance drops and the cycle can repeat. This is a more reliable and quiet design that does not require strict adherence to installation orientation.
What is the difference between the top and bottom connections?
Relays can have different mounting designs. Some models are rigidly fixed to the compressor housing and have a strictly defined position (for example, with the rod down), others are connected via wires and can be installed arbitrarily. Incorrect installation of the electromagnetic relay can lead to the core not lowering and not opening the starting winding, which will cause humming and overheating.
External signs of a relay malfunction
Diagnostics often begin long before opening the engine compartment, since a relay malfunction manifests itself in characteristic symptoms during operation refrigerator. If you notice that the unit turns on, hums for a few seconds, then makes a clicking sound and turns off, this is a classic sign of a starting problem. In such cases, the compressor may be fully operational, but the lack of starting winding does not allow it to develop the required speed.
Another important indicator is the temperature of the compressor housing. If the motor is hot, but there is no cold in the chambers, this indicates that current is supplied to the windings, but the motor does not start or operates in short circuit mode. Thermal relay at this moment the power should be activated and turned off to prevent fire, after which the cycle is repeated after a while when the plate has cooled.
Visual inspection can also provide a lot of information. If, when removing the casing, you find a melted relay body, blackened contacts, or smell a burning smell, further inspection may not be necessary - the part requires replacement. Also pay attention to the integrity of the wires going to the terminals: oxidation or a break can simulate a malfunction of the device itself.
Preparation for diagnostics and safety measures
Before starting any work on the electrical components of the refrigerator, you must strictly follow the safety rules. The first step should always be to completely disconnect the appliance from the power supply. It is not enough to simply turn off the refrigerator with a button, if there is one - you need to unplug the cord from the outlet to eliminate the risk of electric shock and damage to measuring instruments.
To carry out high-quality diagnostics, you will need a minimum set of tools. The main device will be multimeter (tester), capable of measuring resistance (Ohm) and checking the integrity of the circuit (continuity). You may also need a screwdriver to remove the back panel, pliers and, possibly, a contact cleaner if you plan not to replace, but to attempt a restoration.
Access to the relay is through the back wall of the refrigerator, where the compressor is located. In some models, for example Indesit or Atlant, you may need to remove the protective plastic cover. Be careful when removing the relay from the compressor terminals: it is tightly seated, and careless movement can damage fragile copper tubes or motor terminals.
☑️ Preparing to test the relay
Visual inspection and mechanical check
After removing the device from the engine compartment, first perform a thorough visual inspection. The housing must not have cracks, chips or signs of thermal effects. If a rattling sound is heard inside the case when shaken, this may indicate destruction of the internal elements or separation of the contacts, which is a 100% sign of a malfunction.
Pay special attention to the contact groups. Carbon deposits, oxidation or melting of the plastic around the terminals indicate poor contact or overload in the circuit. In electromagnetic relays, check the mobility of the core: it should move freely inside the coil without getting stuck. If the core is jammed in the upper position, the starting winding will not turn off, which will lead to engine combustion.
For a relay with a posistor, visual diagnostics are less informative, since the ceramic element has no moving parts. However, if you see traces of soot on the posistor itself or its terminals, this indicates that a current significantly exceeding the rated current passed through it, or a breakdown occurred. In such cases, replacement is inevitable, since it is impossible to restore the properties of the ceramics.
⚠️ Attention: If you find that the relay contacts are heavily melted, do not try to clean them with sandpaper and install them back. Even if contact appears, the contact area will be less than the nominal one, which will lead to reheating and possible fire in the near future.
Checking with a multimeter: step-by-step instructions
The most accurate result is obtained by instrumental testing using a multimeter. Switch the device to resistance measurement mode (usually 200 Ohm or 2 kOhm range). First, check the integrity of the thermal protection circuit. Connect the probes to the corresponding relay contacts (often they are labeled or located opposite each other). The device should show a value close to zero (for example, 0.1–1.0 Ohm), which means the integrity of the circuit. If there is a unit or an infinity sign on the screen, the circuit is broken and the relay is faulty.
Next, we check the starting circuit. Depending on the design, the resistance of the coil or posistor must be within a certain range. For electromagnetic relays, the coil resistance is typically 10–30 ohms. For posistors in a cold state, the resistance is also low (20–50 Ohms), but the key point here is the response to heating. However, at home, it is difficult to check the change in resistance of a posistor when heated, so they focus on the absence of a break in a cold state.
It is also important to check whether the relay does not “break through” to the housing. Press one probe of the multimeter to the metal body of the relay (if there is one) or to the common wire, and the other to each of the contacts in turn. The device should show infinite resistance. If you see any values, it means that isolation has occurred, and using such a relay is life-threatening.
Table of typical values and faults
For diagnostic convenience, a table is provided below to help interpret instrument readings and visual signs. Please note that the values may vary slightly depending on the manufacturer and model of the compressor. Test type. Normal reading. Malfunction symptom. data-i="108">Thermal protection resistance compressor.
| Type of check | Normal reading | Symptom of malfunction | Action |
|---|---|---|---|
| Thermal protection resistance | 0.1 – 2.0 Ohm | Infinity (break) | Replacing the relay |
| Trigger coil resistance | 10 – 40 Ohm | Infinity or 0 Ohm | Replacement of relay |
| Visual inspection of contacts | Clean metal, no carbon deposits | Black carbon deposits, melting | Replacing the relay |
| Checking for breakdown (housing) | Infinity | Any resistance value | Urgent replacement |
If your measurements coincide with the “Symptom of Malfunction” column, then there can be no doubt about the need for replacement. Even if the refrigerator starts working after reinstallation, the probability of another breakdown in the near future is 99%. There is no point in saving on this part, since the risk of burning out an expensive compressor is too great.
Replacement and features of choosing a new part
When purchasing a new relay, it is necessary to take into account not only the brand of the refrigerator, but also the parameters of the compressor itself. The main criteria are the engine power (in watts or horsepower) and the type of coolant. Often the relay body is marked, for example PTC 18-36, where the numbers indicate the power range. Installing a relay with an inappropriate range will either prevent the compressor from starting or cause it to overheat.
The installation process is simple: the new device is put on the three terminals of the compressor (common, starting, working) according to the diagram, which is usually shown on the case or in the instructions. It is important to ensure a tight fit of the contacts. If the relay is electromagnetic, strictly observe its spatial position (vertical, horizontal) specified by the manufacturer, otherwise the mechanism will not work correctly.
After installation, reassemble everything in the reverse order, connect the refrigerator to the network and listen. The launch should be confident, without a long hum. After 10-15 minutes of operation, check the temperature of the compressor housing and the relay itself - they may get hot, but should not be hot. If everything is in order, the refrigerator can be loaded with food.
⚠️ Attention: Technical characteristics of compressors and compatible relay models may vary even within the same series of refrigerators. Before purchasing, be sure to check the markings on the old relay or consult the technical documentation of your device.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a start relay?
Theoretically, start The compressor can be applied by manually applying voltage to the starting winding for a short time, but operating the refrigerator in this mode is strictly prohibited. This will lead to rapid burning of the motor windings due to the lack of shutdown of the starting phase and overload protection.
Why does a new relay burn out a week after replacement?
A common reason is incorrect selection of relay power or a malfunction of the compressor itself (interturn short circuit, jamming). The problem may also be power surges in the network or poor contact in the connector, which causes sparking and heating.
What is the difference between the relay for R600a and R134a compressors?
The main difference is often in the power and response current, since compressors using different refrigerants have different characteristics. In addition, compressors based on R600a (isobutane) are more sensitive to sparking, so increased demands are placed on the quality of contacts and the intrinsic safety of the relay.
Is it possible to repair a relay if the contacts are burnt?
In modern conditions, repairing a relay is impractical. Stripping the contacts gives a temporary effect, but disrupts the geometry and coating of the silver, which leads to rapid re-burning. The cost of a new part is low, so replacement is the only reliable solution.