The situation when the refrigerator stops working cool, and only clicks or a humming sound is heard inside the compressor, which ends abruptly, is familiar to many owners of household appliances. Often the reason for this behavior is not a breakdown of the motor itself, but the failure of a small but critical element - the starting relay. It is this component that provides the necessary impulse to start the compressor engine, and its failure paralyzes the operation of the entire cooling system.
Before calling a technician or rushing to the store for a new unit, it makes sense to conduct independent diagnostics. Checking the start relay is a procedure that is accessible even to a beginner and does not require complex professional equipment, except, perhaps, a multimeter. Start relay is responsible for supplying voltage to the starting winding of the engine at the moment of switching on, and then turns it off when the motor picks up operating speed.
In this article We will analyze in detail how to visually and instrumentally assess the condition of the part, what symptoms indicate its malfunction, and whether it is possible to extend the life of the device by simply cleaning the contacts. Understanding the operating principle of this unit will help you save significant money on repairs.
Symptoms of a faulty starting relay
You can determine that the problem lies in the starting system by the characteristic signs that appear in the operation of the compressor. Often, users confuse these symptoms with a breakdown of the motor itself, which leads to unnecessary expenses. Characteristic clicks, repeated at regular intervals, are the first bell.
If you hear the refrigerator humming for a few seconds, and then there is a loud click and silence, this indicates the fact that the engine is trying to start, but the starting winding does not receive the required impulse or the current in the circuit is too high. In such a situation, the thermal protection relay opens the circuit, preventing the windings from burning out.
⚠️ Attention: If the compressor hums but does not start, and its housing becomes very hot, immediately disconnect the device from the network. Long-term operation in this mode can lead to an interturn short circuit and complete failure of the motor.
Another obvious sign is the complete lack of response of the unit to being connected to the network, although the lighting in the chamber is on. In some cases, the relay may “stick” when turned on, causing the compressor to operate continuously without turning off, which leads to freezing of food and the formation of an ice coat.
Design and principle of operation of the mechanism
In order to carry out a quality diagnosis, you need to understand how this small plastic block, attached to the side of the compressor, works. Inside the housing there is an electromagnetic coil and a movable core that closes the contacts of the starting winding. There are also devices with a posistor, where the role of a switch is played by a temperature-sensitive element.
In classic induction relays, the current passing through the working winding creates a magnetic field that draws in the core. At this moment, the starting winding circuit closes and the motor rotor begins to rotate. As soon as the speed reaches 75% of the nominal value, the current drops, the core drops under the influence of gravity, opening the starting circuit.
What is the difference between different types of relays?
Induction relays work due to the electromagnetic field and a moving core, while posistor relays use the property of the material to sharply increase resistance when heated. PTC models are considered more reliable and do not depend on the position of the refrigerator, but induction ones are easier to diagnose visually.
It is important to note that thermal protection relayis also often located inside the case. This is a bimetallic plate that opens the circuit when the compressor overheats. When diagnosing, it is often necessary to check both elements, since they can be combined into one unit or otherwise coupled.
Visual inspection and preparation for diagnosis
The first stage of any diagnosis is a thorough visual inspection. Before removing the part, make sure the refrigerator is unplugged. Carefully remove the rear cover of the unit to gain access to the compressor, and remove the casing covering the contacts.
Remove the relay from the contact group of the compressor. Usually it is simply put on three pins and secured with a bracket or clamps. Carefully inspect the plastic case: there should be no cracks, signs of burning or melting. If you see black spots or smell burnt plastic, further inspection may not be necessary - the element requires replacement.
- 🔍 Inspect the internal contacts for oxidation, carbon deposits or corrosion.
- 🔍 Check the integrity of the wires going to the terminals for breaks.
- 🔍 Shake the relay near your ear: if you hear a clear knocking sound of a detached core or debris, the part is faulty.
Pay special attention to the contact group on the compressor itself. If the relay contacts were burnt, then a similar deposit could remain on the motor pins. They must be carefully cleaned with fine sandpaper or a file before installing a new element, otherwise the problem will repeat.
Instrumental testing with a multimeter
The most accurate result is obtained by checking with a multimeter. This device will allow you to assess the integrity of the windings and the condition of the contacts with high accuracy. Switch the multimeter to resistance measurement (Ohm) or continuity mode.
For induction relays, check the coil resistance. The probes of the device are applied to the corresponding contacts. If the device shows infinity (one in the most significant digit or an overload symbol), it means that there is a break in the coil, and the relay will not be able to create a magnetic field to start.
⚠️ Attention: Never carry out resistance or continuity measurements on a device connected to the power supply. This will cause the multimeter to fail and can be life-threatening.
Next, you need to check the contacts. In the initial position (the relay is turned upside down or lies on its side, simulating operation), the contacts of the starting circuit must be open. If the multimeter shows a short circuit (0 Ohm) without voltage supply, it means that the contacts are “stuck” or the core is jammed.
☑️ Multimeter testing algorithm
If you are checking a relay with a posistor, the resistance of the posistor itself in a cold state should be several tens of Ohms (usually 4-45 Ohms depending on the model). If the resistance is close to zero or infinity, the element is faulty.
Table of normal resistance values
For ease of diagnosis, below is a table with approximate resistance values for various types of elements. Remember that the exact data depends on the specific refrigerator model and compressor manufacturer.
| Element type | Normal resistance | Fault symptom |
|---|---|---|
| Inductive relay coil | From 1 to 10 Ohm | Infinity (break) or 0 (short circuit) |
| Posistor (cold state) | From 4 to 45 Ohm | Values out of range, instability |
| Thermal relay (bimetal) | About 0 Ohm (closed) | Infinity (open circuit) |
| Starting circuit contacts | Depends on position | Sticking or lack of contact |
Using this data, you can quickly weed out obviously faulty parts. However, it is worth considering that some defects appear only under load or when heated, so even normal resistance readings do not provide a 100% guarantee of serviceability, although they are a strong indicator.
Diagnostic nuances for different types of relays
Modern refrigerators can be equipped with different types of starting devices, and each of them has its own characteristics. For example, RTP relay (Thermal Start Relay) is often found in older models and combines starting and protection functions. It is important to check not only the coil, but also the condition of the bimetallic plate.
Posistor relays, such as PTC-Start, are more compact and do not have moving mechanical parts inside. Their failure is often associated with degradation of the ceramic element. Visually, traces of burning are not always visible on the posistor, so checking the resistance here is critically important.
In some models of refrigerators with inverter compressors, there may not be a classic starting relay at all - its functions are performed by an electronic control unit. In such cases, diagnostics with a multimeter is not applicable, and more complex equipment is required for signal analysis.
⚠️ Attention: If your refrigerator has an inverter compressor (works without characteristic clicks and stops, smoothly changing power), an attempt to find and test the classic start relay will be unsuccessful, since its functions are integrated into the electronics.
When replacing, try to select an analogue with identical characteristics. Installing a relay with other parameters can lead to rapid failure of the new element or damage to the compressor.
Common mistakes when replacing yourself
Replacing a relay seems like a simple operation, but beginners often make mistakes that nullify all efforts. The most common one is ignoring the orientation of the part. Many relays only work in a certain position relative to the axis of the globe, since the core must fall freely under the influence of gravity.
Another mistake is installing the part “at random” without checking the compressor contacts. If you place a new relay on oxidized or burnt motor pins, the contact will be poor, sparking will occur, and the new relay will burn out after a few days or even hours of operation.
- 🚫 Trying to clean the contacts with sandpaper without turning off the power.
- 🚫 Installing the relay upside down (for models with gravity mechanism).
- 🚫 Ignoring checking the capacitor if it is in the circuit.
Also, do not neglect checking the capacitor, which is often paired with a starting relay in circuits with two windings. If the capacitor is swollen or has lost capacity, the relay will operate in extreme mode, which will shorten its life.
Is it possible to temporarily start a refrigerator without a relay?
Theoretically, you can apply voltage to the starting winding manually for 1-2 seconds, but this is extremely dangerous and requires qualifications. An inexperienced user may receive an electric shock or damage the compressor. It is not recommended to do this without special knowledge.
Is it possible to repair a burnt relay, or is it only necessary to replace it?
In most cases, repair is impractical. If the coil burns out or the housing is deformed, the part must only be replaced. Sometimes cleaning the burnt contacts helps, but this is a temporary measure, since the metal structure is already damaged and sparking will resume.
Why does a new relay burn out a week after installation?
Most often, the reason lies in a malfunction of the compressor itself (an interturn short circuit, a wedge of the piston group) or problems with the wiring. It is also possible that a relay with unsuitable current or voltage characteristics was selected.
Where can I find the markings for selecting an analogue?
The markings are usually applied to the side or top edge of the plastic relay case. Look for codes like RT, RCT, PTC followed by numbers. The model number of your refrigerator is also important, by which you can select a compatible spare part in catalogs.