A sudden stop in the operation of refrigeration equipment often takes people by surprise, leaving products without the necessary storage conditions. One of the key elements responsible for starting and operating the compressor is thermal relay (or start-up relay). It is this small unit that supplies the starting impulse to the engine, allowing the system to gain speed and begin circulating the refrigerant. If the refrigerator hums but does not start, or, conversely, clicks and immediately goes silent, there is a high probability of a malfunction in this particular component.
Before calling a technician or buying a new part, it makes sense to carry out the initial diagnostics yourself. To do this, you will need a basic tool - a multimeter, which allows you to measure electrical resistance and circuit integrity. Refrigerator thermostat - the device is inexpensive, but its replacement requires accuracy, so correct diagnosis will help avoid unnecessary expenses. In this article we will analyze a detailed algorithm of actions that will allow you to determine the performance of the part.
It is worth noting that working with electrical appliances requires compliance with basic safety rules. Any manipulations inside the housing should be carried out only after the unit is completely disconnected from the power supply. Even after removing the plug from the socket, a residual charge may remain in the capacitors, so you should not touch the compressor terminals with bare hands without first discharging if you are not sure of your actions.
The operating principle and design of the start-up relay
To effectively test the element, you need to understand its internal logic. Classic models of refrigerators Indesit, Atlant or Beko use electromagnetic relays. They are based on a coil through which current passes to the motor windings. When starting, the current is high, the magnetic field draws in the core, which closes the contacts of the starting winding. As soon as the motor picks up speed, the current drops, and the core, under the influence of gravity or a spring, opens the circuit.
Thermal protection operates in parallel with the starting function. This is a bimetallic plate that reacts to the heating of the compressor housing. If the motor overheats due to a power surge or jamming, the plate bends and opens the power circuit, preventing the windings from burning out. Thermal relay in this case it acts as a fuse, and its integrity is also critical to the operation of the system.
There are also solid-state options, such as called PTC starters. They have no moving parts, and the role of a switch is performed by a ceramic element that changes its resistance when heated. Testing such devices with a multimeter has its own nuances, but the basic principle of searching for an open circuit or short circuit remains the same. Understanding the type of your relay will help you choose the right testing tactics.
⚠️ Attention: In some modern models, the starting and thermal relays are combined into one housing, while in older versions they can be separated. Visually inspect the assembly before disassembling to avoid damaging the fragile contacts during dismantling.
Differences in design affect the location of the contacts. In electromagnetic models you will see a moving core and coil, and in solid-state models you will see a monolithic bar with three leads. Regardless of the design, the task of the unit is the same: to apply high voltage to the starting winding at the first moment and turn it off after a second. If this cycle is broken, the compressor either will not start or will hum, trying to move away.
Necessary tools and safety measures
To carry out high-quality diagnostics, you do not need complex professional tools. The main device will be a multimeter (tester) capable of operating in ohmmeter mode. It is advisable that the device have audio dialing, as this allows you not to be distracted by looking at the screen while manipulating the wires. You should also have pliers, a screwdriver and possibly fine-grained sandpaper on hand for cleaning the contacts.
- 🔧 Multimeter: a device for measuring resistance, voltage and current.
- 🔌 Screwdriver: for removing protective covers and terminal blocks.
- 🧤 Dielectric gloves: for additional protection when working with electrical equipment.
- 📸 Smartphone: to photograph the connection diagram before dismantling.
Safety is priority number one. Before starting any work, make sure that the refrigerator is completely unplugged. Even if you simply remove the back cover near the compressor, there is still a risk of accidentally touching live parts. In addition, there may be sharp metal edges in the compressor area, so be careful not to injure yourself.
It is important to ensure good lighting of the work area. The compressor compartment is often dark, and the markings on the wires may be small. Use a flashlight or extra lamp. If you are working in a damp environment (such as a garage or basement), make sure the floor is dry and you are standing on a dielectric mat or wooden stand.
Removing the thermal relay for inspection
The process of removing the relay begins by removing the rear protective panel of the refrigerator. It is usually secured with latches or several screws. After removing the panel, you will see a black or gray cylindrical tank - this is the compressor, and at its end or side there is a small box to which the wires fit. This is our desired node.
First of all, you need to photograph the location of the wires. Color coding may not comply with standards, and it is very easy to mix up the contacts during assembly. Remember or write down which wire goes to which pin. Then carefully disconnect the wiring harness. Often it sits tightly, so you can slightly rock it from side to side, but do not pull on the wires themselves, so as not to break them at the base.
☑️ Checklist before dismantling
The relay itself is removed from the three pins of the compressor. It can be held in place by a tight fit or secured with a metal bracket. If there is a bracket, it must be carefully bent. The relay must be pulled strictly along the axis of the pins, without distortions, so as not to break the ceramic base or the contacts themselves on the compressor. If the relay does not work, do not use excessive force - it is better to check again for the presence of fixing elements.
⚠️ Attention: When removing the relay, be careful with the wires going to the temperature sensor, if it is built into the structure. A sharp jerk can damage the thin wires, and then not only the relay, but also part of the wiring will need to be replaced.
After removal, inspect the relay body. There should be no traces of burning, melting or cracks on it. If you smell burnt insulation or see black residue on the contacts, this is a sure sign of a malfunction. However, appearance does not always indicate the internal state, so we move on to instrumental testing.
Algorithm for testing with a multimeter
Setting up a multimeter is the first step. Switch the device to resistance measurement mode (denoted as Ω or Ohm). Select a limit of 200 Ohms or dial-in mode (with speaker). If you are testing thermal protection, the limit can be set higher, up to 2 kOhm, since the resistance of the bimetallic strip may be small, but not zero.
Checking the starting winding (pins 1-3 on the standard circuit) should show low resistance, usually in the range of 3 to 15 Ohms, depending on the power of the compressor. If the multimeter shows one (infinity), it means there is an open circuit and the relay is faulty. If it shows zero, there may be a short circuit, which also requires replacement.
Thermal protection (contacts 1-2) in a cold state should ring, showing a resistance close to zero (0.1–1 Ohm). This means that the circuit is closed and current can flow. If there is a break here, the compressor will not receive power at all. The check must be carried out by touching the corresponding contacts on the relay itself with probes, and not on the wires.
Nuances of checking PTC starters
In solid-state relays, the resistance can “float” when heated. When cold it should be low (20-50 ohms). If you see hundreds of ohms or a break, the element has burned out. Also, the PTC element may crack inside the housing, which will be heard when shaken.
For more accurate diagnostics, you can turn the relay over. In electromagnetic models, the core must move freely inside the coil. If it is stuck, the contacts may not open or close. Lightly tap the body on the table - if you hear the ringing of a freely moving element, this is a good sign. A dull knock may indicate destruction of the internals.
There is a table of typical resistance values for various components, which will help you navigate the device readings. Remember that there are no ideal values, and there is always a manufacturer’s tolerance, but strong deviations indicate a problem.
| Type of circuit being measured | Normal reading | Failure sign | Action |
|---|---|---|---|
| Start winding | 3 – 15 Ohm | ∞ (infinity) or 0 | Relay relay |
| Thermal protection (cold) | 0 - 1 Ohm | ∞ (open circuit) | Replacing the relay |
| PTC element | 10 - 50 Ohm | > 100 Ohm or 0 | Replacing the starter |
| Case insulation | ∞ (Megaohms) | Any value | Dangerous, breakdown to the case |
If after checking you find that all resistances are normal, but the refrigerator still does not work, the problem may be deeper. The compressor itself may be faulty (interturn short circuit) or the thermostat. However, the serviceability of the relay is already a big step towards solving the problem, eliminating one of the main causes of failure.
Typical faults and their symptoms
One of the most common problems is sticking of contacts. This happens when a spark melts the metal when the circuit opens, and the contacts are welded. In this case, the starting winding remains on constantly, which leads to overheating and eventual combustion of the engine. The sign is a buzzing sound and a subsequent click of the thermal protection after a few seconds.
The second common case is the destruction of the bimetallic plate of the thermal protection. It can lose its properties over time and repeated heating and cooling cycles. The plate stops opening when overheated or, conversely, opens at normal temperature. Refrigerator in this case, it may either burn out or not turn on at all, even if it is working properly.
- 🔥 Overheating: the relay body is too hot to the touch after operation.
- 🔊 Noise: loud humming or buzzing when trying to start.
- ❄️ No cold: the compressor is silent, although the chamber is warm.
- ⚡ Knocking out plugs: a short circuit inside the relay causes the circuit breakers in the panel to trip.
It is also worth mentioning the oxidation of contacts. Over time, copper becomes covered with an oxide film, which does not conduct current well. This creates additional resistance, heat and unstable operation. Cleaning the contacts sometimes helps, but in conditions of high humidity and vibration the effect will be temporary. It is better to replace the entire assembly.
It is important to distinguish between a relay malfunction and a compressor malfunction. If, when power is applied directly (which should only be done by an experienced technician), the compressor does not start or hums, the problem is in the motor. If the motor starts and works normally without a relay, but does not start with a relay, the relay is to blame.
Replacement and installation of a new component
If the diagnostics showed a malfunction, the relay must be replaced. The selection of an analogue is carried out according to the markings indicated on the body of the old device. Codes usually consist of letters and numbers (for example, RT, PTR, 115L). It is important to consider the orientation of the pins and the type of compressor (horizontal or vertical), since in some relays the position of the core is dependent on gravity.
Installation is done in the reverse order. Slide the new relay onto the compressor pins as far as they will go. Make sure it fits snugly and doesn't wobble. If a retaining bracket was used, replace it in place. Then connect the block with wires according to the photo or diagram taken earlier.
⚠️ Attention: Do not confuse the polarity of the connection if it matters for your model (although for most starting relays this is not critical, for thermal and combined ones the correct position is important). Follow the markings
L(Line),S(Start),R(Run).
After assembly, do not rush to close the back panel. Plug in the refrigerator and listen. There should be a characteristic click, then the hum of the motor starting, and after a few seconds the second click of the starting winding turning off. If the process went exactly like this and the cold started, you have completed the task successfully.
Frequently asked questions (FAQ)
Is it possible to repair a thermal relay, or just change it?
In most cases, repairs are not economically feasible. The cost of a new relay is low, and restoring contacts or replacing the coil inside requires high qualifications and special materials. It is easier and more reliable to install a new part.
Why does a new relay burn out a week after replacement?
This may indicate problems with the compressor itself (difficult starting, interturn short circuit) or unstable voltage in the network. It is also possible that a relay with inappropriate characteristics is installed (wrong current or type).
Where can I find the relay markings if they are erased?
If the markings on the body are not readable, you can try to find the compressor model and select a relay from compatibility catalogs for this series of engines. A photograph of the internal structure for consultation with a specialist will also help.
Is it dangerous to operate a refrigerator with a faulty relay?
Yes, it is dangerous. A faulty relay can lead to overheating and a fire in the wiring or the compressor itself. In addition, constant attempts to start the compressor, which can damage the expensive motor.