A sudden stop of the compressor or its refusal to start often becomes an unpleasant surprise, especially when perishable products remain in the chamber. In most cases, the culprit of the breakdown is not the motor itself, but start-up protection relaywhich ensures safe start and operation of the unit. This small but critical element protects the motor windings from overheating and overcurrent, opening the circuit when dangerous situations arise.
Understanding this how to check the thermal relay of a refrigeratorwill allow you to save a significant amount on calling a technician and quickly bring your equipment back to life. Diagnostics of this unit does not require complex professional equipment, just basic knowledge of electrical engineering and a simple measuring instrument. In this article, we will analyze in detail the device of the element, signs of its failure and an algorithm of actions for accurate diagnosis.
Before starting disassembly, you need to make sure that the refrigerator is disconnected from the power supply, since working with electrical components under voltage is deadly. Safety is the first rule any DIYer, which, if neglected, could result in serious injury or damage to the appliance's electronics. After removing the plug from the retail outlet, you can begin to visually assess the condition of the external elements.
⚠️ Attention: Before starting any work, make sure that the capacitors in the control circuit are discharged and the compressor has cooled down to avoid burns or electric shock from residual charge.
Design and principle of operation of the starting protection relay
For effective diagnostics, it is necessary to clearly understand what exactly is inside the plastic case attached to the compressor casing. Thermal relay the starting device consists of a bimetallic plate that bends under the influence of the temperature that occurs when the passage of electric current through the motor windings. If the current exceeds the permissible limits, the plate heats up, bends and opens the contacts, stopping the power supply.
In parallel with the thermal protection, a trigger mechanism is often located in the housing, which can be inductive or posistor. Modern models most often use posistors semiconductor elements that sharply increase their resistance when heated, which automatically turns off the starting winding after the motor starts. Understanding the differences between these types is important, as the methods for testing them may differ slightly.
The relay body is usually marked with the model and technical characteristics, such as operating current and voltage. This data is necessary for selecting an analogue in case of replacement, since installing an unsuitable element can lead to repeated breakdown or even fire of the wiring. Rated current must strictly comply with the parameters of the specific compressor specified in the technical documentation of the refrigerator.
Differences between induction and posistor relays
Induction relays use an electromagnetic coil to open contacts and have moving mechanical parts that wear out over time. PTC devices do not have moving contacts in the starting circuit, operate silently and are considered more reliable, but are sensitive to power surges in the network.
Main signs of a faulty protective device
You can determine that the problem lies in the relay by the characteristic symptoms that appear when you try to turn on the refrigerator. Most often, owners are faced with a situation where the compressor hums for several seconds, after which a click is heard and the motor stops. This cycle can be repeated with a certain periodicity, which indicates the activation of the starting winding or the lack of activation of the thermal protection. Another clear sign is the complete lack of reaction of the refrigerator when plugged into the network, provided that the socket and power cord are in good working order. In some cases, you may notice strong heating of the compressor housing or the relay itself, which indicates the constant passage of current through the thermal protection and its inability to open the circuit in time. thermal protection or failure to start the starting winding.
Another obvious sign is the complete lack of reaction of the refrigerator when plugged in, provided that the outlet and power cord are in working order. In some cases, you may notice strong heating of the compressor housing or the relay itself, which indicates a constant flow of current through the thermal protection and its inability to open the circuit in time. Overheating is dangerous because it can lead to melting of plastic elements and a short circuit.
- 🔊 The compressor hums for 3-5 seconds, then there is a click and there is silence.
- 🔥 The housing of the start relay or compressor becomes excessively hot to the touch.
- 💡 The light in the refrigerator compartment is on, but the engine does not start at all.
- ⚡ Triggering circuit breakers in the apartment's electrical panel when the device is turned on.
It is important not to confuse a relay malfunction with a breakdown of the compressor itself, since the symptoms may be similar. If after replacing the relay the situation has not changed, there may be an interturn short circuit in the motor windings or the piston group is jammed. In such cases, a more in-depth diagnosis is required by measuring the resistance of the windings and the pressure in the system.
Preparation for diagnostics: tools and safety
A high-quality check is impossible without the appropriate tools, which should be on hand before disassembling the unit. The main diagnostic device is multimetr (tester), which allows you to measure resistance, circuit integrity and voltage. It is desirable that the device has an audible dialing function, as this significantly speeds up the process of troubleshooting in the field.
In addition to measuring equipment, you will need a set of screwdrivers for removing the rear panel of the refrigerator and dismantling the compressor casing. On some models, access to the relay is difficult and you may need to carefully move the unit away from the wall, being careful with the copper condenser tubes. Mechanical strength The tubes are low and damage to them will lead to refrigerant leakage and costly repairs.
Be sure to prepare personal protective equipment such as dielectric gloves if you plan to take measurements with the device turned on (which is highly not recommended for beginners). You should also have dry rags and an alcohol-containing liquid on hand to clean the contacts from oxides and dirt before testing. Clean contacts ensure accurate measurements and a reliable connection after assembly.
☑️ Tools for testing relays
Removing the relay and visual inspection
The process of removing the relay begins with removing the protective cover located at the bottom of the rear wall of the refrigerator. It is usually secured with latches or screws that must be carefully unscrewed without using excessive force to avoid damaging the threads. After removing the cover, you will see a compressor with a black or white plastic block attached to its rod or next to it - this is the device you are looking for.
To remove the relay, you need to disconnect the connector with the appropriate wires and carefully remove the block itself from the contact group of the compressor. In some models, it is fixed with a metal bracket or a spring clip that needs to be bent. Contact group Must be inspected for traces of carbon deposits, plastic melting or corrosion, which often cause poor contact.
⚠️ Attention: When removing the relay, avoid sharp jerks and impacts on the case, since inside there are fragile bimetallic plates and ceramic elements that can be easily damaged if handled carelessly.
Visual inspection can immediately answer the question about the operability of the device. If traces of burning are visible inside the housing, the smell of melted insulation is felt, or cracks are visible on the housing, then such a relay definitely requires replacement. However, the absence of external defects does not guarantee serviceability, so instrumental control is necessary.
Method of checking with a multimeter: step-by-step instructions
The most accurate diagnostic method is to check the electrical resistance using a multimeter. To begin, switch the device to resistance measurement mode (Ohm) or continuity mode. If you are checking thermal protection, connect the probes to the input and output contacts of the relay: a working device should show a resistance close to zero or emit a sound signal.
When checking a starting posistor relay, the situation is different: a cold posistor should have a low resistance (usually from 5 to 50 Ohms), which increases when heated. If the multimeter shows infinity (one in the most significant digit) on a cold element, it means that the circuit is broken and starting the compressor is impossible. Resistance is a key parameter by which the integrity of the internal circuits is judged.
For induction relays, it is important to check the absence short circuits to the body and integrity of the coil. The coil resistance must be within the limits specified in the technical documentation, usually several ohms. If the device shows a short circuit (0 Ohm) or an open circuit, the relay is considered faulty and must be disposed of.
Table of typical values and possible faults
For the convenience of analyzing measurement results, it is recommended to check the typical values typical for serviceable and faulty elements. Below is a table that helps interpret the multimeter readings and determine the nature of the breakdown.
| Test type | Indications of a working relay | Indications of a faulty relay | Probable cause |
|---|---|---|---|
| Thermal protection (cold) | 0 Ohm (Sound) | Infinity (Open) | Bimetallic plate burned out |
| Posistor (starting) | 10-40 Ohm | 0 Ohm or Infinity | Crystal breakdown or destruction |
| Induction coil | Several Ohm | 0 Ohm or Infinity | Interturn short circuit or open circuit |
| Contacts on the body | Infinity | Any value | Insulation breakdown, dangerous! |
Analysis of the data obtained allows us to make a final conclusion about the need to replace the component. If the multimeter readings coincide with the “Faulty relay” column, further operation of the refrigerator with this element is impossible. Diagnostics is completed, and you can proceed to the search for a suitable spare part.
Replacement and selection of a new relay
The purchase of a new relay should be carried out strictly according to the marking of the old device, since there are no universal solutions for all compressors. The housing is usually stamped with numbers indicating the operating current (for example, 1.3A, 1.6A) and compatible series of compressors (Danfoss, Secop, Atlant). Compatibility Current is critical: a relay with a lower current will constantly turn off the motor, and with a higher current it will not protect it in case of overload.
The process of installing a new element is carried out in the reverse order of dismantling. It is important to firmly seat the relay on the compressor contacts until a characteristic click is heard and securely fix it with a bracket or screws. After assembly, make sure that all wires are connected correctly and do not touch hot parts of the compressor or sharp edges of the housing.
The first start-up after repair should be carried out under supervision, monitoring the engine starting and the absence of extraneous sounds. If the compressor started confidently and after some time the temperature in the chamber began to decrease, it means it was successful. Otherwise, repeated diagnostics or contacting professionals will be required. repair was successful. Otherwise, repeated diagnostics or contact with professionals will be required.
⚠️ Attention: Technical characteristics of compressors and compatible relays may vary depending on the year of manufacture and the specific modification of the refrigerator. Always check the markings on the body of your device with the manufacturer's catalog data before purchasing spare parts.
Is it possible to temporarily close the relay to start the refrigerator?
It is strictly not recommended to operate the refrigerator with a shorted or removed thermal relay. This deprives the compressor of protection from overheating, which can lead to ignition of the windings and a fire in a matter of minutes. This method is only permissible for a short-term check of the performance of the motor itself.
Why does a new relay burn out immediately after installation?
Most often this indicates a malfunction of the compressor itself, which consumes too much current (starting or operating). Also, the reason may be an incorrect selection of relay for the current or the presence of problems with the voltage in the apartment’s electrical network.
How often do you need to change a thermal relay?
The service life of a high-quality relay is designed for the entire life of the refrigerator, however, voltage surges and frequent temperature changes can shorten its life. Replacement is carried out only upon the fact of a malfunction; planned preventative replacement is usually not required.