Sudden stoppage of the compressor or characteristic clicks when trying to start the refrigerator often indicate problems with the start-protection relay. This small but critical element of the electrical circuit is responsible for starting the engine and protecting it from overheating. If the relay fails, the compressor either does not start at all, or turns on for a few seconds and stalls again, which can lead to serious damage to the motor.
Checking this component with a multimeter is one of the basic procedures in the arsenal of a home mechanic, which allows you to save time and money on calling a specialist. Diagnostics takes only a few minutes, but requires strict adherence to safety precautions and understanding the principles of operation of an electrical circuit. In this article, we will analyze the algorithm of actions in detail, help you decipher the markings and avoid common mistakes when testing.
Before you start disassembling, make sure that you have basic skills in working with power tools. Multimeter must be in good working order, and the probes must be intact isolation. Remember that working with electrical appliances under voltage is strictly prohibited, so the first step is always to completely disconnect the device from the power supply.
Principle of operation and types of relays
The starting protection relay is an electromechanical device that automatically turns on the starting winding of the compressor at the moment of startup and turns it off after gaining speed. At the same time, it acts as a thermal fuse, opening the circuit when the engine overheats. There are two main types of these devices, each of which has its own design and testing features.
The first type is induction (current) relay. They work on the principle of an electromagnet: when current is applied to the main winding, the core is retracted and closes the contacts of the starting winding. When the engine picks up speed, the current drops, the core releases the contacts, and the starting winding is turned off. Such models are often installed on older models of refrigerators.
The second type is posistor relays. In them, the switching function is performed by a thermistor (posistor). When voltage is applied, it heats up, its resistance increases sharply, and the current practically stops flowing to the starting winding. Posistors They are considered more reliable, since they do not have moving mechanical parts subject to wear.
Why do relays fail?
The main cause of failure is overheating of the contacts or degradation of the posistor. Frequent power surges in the network and compressor overload due to a dirty capacitor also reduce the service life of the element.
External inspection and preparation for diagnostics
Before using measuring instruments, it is necessary to conduct a visual assessment of the condition of the part. Remove the back cover of the refrigerator, find the compressor and carefully remove the plastic casing covering the electrical part. The relay is usually mounted on the side of the motor or on the frame next to it.
Carefully inspect the housing for melting, cracks or burn marks. If you notice black carbon deposits or smell burnt plastic, this is a sure sign that the part needs to be replaced. Also check the condition of the contacts: oxidation or burning of the metal may interfere with the normal conduction of current.
⚠️ Attention: If the relay body is swollen or black dust spills out of it when slightly shaken, further checking with a multimeter does not make sense - the element is clearly faulty and requires replacement.
For correct testing with a multimeter you need to remove the relay from the compressor. It is usually secured with a bracket or latches. Carefully disconnect the wires, having previously photographed their location, so as not to confuse the terminals during assembly. Marking contacts will help you navigate the circuit.
☑️ Initial inspection of the relay
Tools and safety measures
To carry out high-quality diagnostics, you will need a digital multimeter with a continuity and resistance measurement mode. Make sure that the device is working properly: connect the probes to each other - zero values should appear on the screen or a beep should sound. You may also need a screwdriver to remove fasteners and pliers.
Safety is priority number one. Even after unplugging the cord from the outlet, there may be some residual charge left in the capacitors. Before touching metal parts of the compressor or wires, it is recommended to wait 5-10 minutes or carefully discharge the circuit (if you know how to do this safely).
Work in a dry area and use tools with intact handle insulation. If there is water or high humidity on the floor, move the work to another place. Electric current does not forgive errors, so eliminate any risk of short circuit.
Algorithm for checking an induction relay
Checking a current relay begins with determining the position of the contacts at rest. Turn the relay over so that the arrow on the housing (if there is one) points up. In this position, the contacts of the starting winding should be open. Connect the multimeter probes to the corresponding terminals - the device should show infinite resistance (number 1 on the left of the display).
Then turn the relay over with the arrow pointing down. The mechanism should operate under the influence of gravity, and the contacts will close. The multimeter in dial mode should emit a beep and the screen should display zero or a value close to it. If this does not happen, it means that the mechanism is jammed or the contacts are burnt.
The thermal relay is checked separately. It is usually located in the same building or adjacent to it. Call his contacts - they should be short calls. If the resistance is high or absent, the thermal protection has burned out. Bimetallic plate The inside could lose its properties due to frequent overheating.
Diagnostics of the posistor relay
Checking the posistor option simpler, since there are no moving mechanical parts that depend on the position in space. First of all, the resistance of the posistor itself is measured. Connect the multimeter probes to the element terminals. When cold, the resistance should be low, usually in the range from 10 to 50 Ohms, although the exact values depend on the model.
If the multimeter shows one (infinity) or, conversely, zero, the posistor is faulty. However, it is worth considering that the multimeter supplies a weak current, insufficient to heat the element and change its resistance. Therefore, the main test is to check for short circuits and breaks.
Also check the integrity of the connections inside the case. It often happens that vibration causes soldering to fall off or an internal fuse to blow, if it is provided for in the design. Visually inspect the board or the insides of the relay for microcracks. Posistor - the element is sensitive to shock, so you need to handle it with care.
Table of typical values and explanation
For ease of diagnosis, we provide a summary table that will help interpret the readings of your measuring device. The values may vary slightly depending on the manufacturer and the specific model of the refrigerator, but the general principles remain the same.
| Check type | Condition | Normal reading | Failure sign |
|---|---|---|---|
| Induction (vertical) | Contacts open | ∞ (Unit) | 0 Ohm (Sticking) |
| Induction (horizontal) | Contacts closed | 0 Ohm (Sound) | ∞ (Open/Scrap) |
| Posistor | Cold state | 10–50 Ohm | ∞ or 0 Ohm |
| Thermal protection | In any position | 0 Ohm (Sound) | ∞ (Burnout) |
Please note that the resistance of the windings of the compressor itself also plays a role. If the relay is working properly, but the engine does not start, the problem may be an interturn short circuit in the motor windings. In this case, the resistance between the compressor terminals will differ from the nominal one or tend to zero.
When selecting an analogue, pay attention not only to the geometric dimensions, but also to the markings. Rated current and the type of refrigerant for which the relay is designed must match the original. Installing an unsuitable part may result in repeated failure.
⚠️ Attention: Relay specifications may vary depending on the year of manufacture of the compressor. Always check the markings with the manufacturer's catalogs or a consultant at a spare parts store before purchasing.
Common mistakes and recommendations
One of the common mistakes is trying to clean the burnt contacts on an induction relay with sandpaper. Do this It is absolutely impossibleas the special coating of the contacts will be damaged, and after a short time they will burn again, but with the formation of persistent carbon deposits that cannot be removed.
Another mistake is ignoring the reasons that caused the relay to break down. If the posistor or contacts burnt out, it means that the compressor was operating in emergency mode (overload, poor condenser ventilation). Simply replacing the relay without eliminating the root cause will result in the new part burning out in a few days or weeks.
When installing a new element, make sure that it fits snugly on the compressor terminals. Poor contact will cause sparking and heating. If the connectors on the wires are melted, they must be replaced or carefully restored using heat shrink for insulation.
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a starting relay?
Theoretically, you can start the engine by applying voltage to the starting winding manually, but this is extremely dangerous and requires qualifications. Operating a refrigerator without a working relay is prohibited, since the compressor will burn out in a few minutes due to overheating of the windings.
Why does a new relay burn out immediately after installation?
This indicates a malfunction of the compressor itself (interturn short circuit, wedge of the piston group) or problems in the electrical network at home. Also, the cause may be an incorrectly selected relay with inappropriate current characteristics.
How to distinguish a posistor relay from an induction relay?
An induction relay makes a slight knocking sound when turned over (the movable core works). The posistor is monolithic, nothing rattles inside. They also differ in the markings and connection diagram indicated on the case.
Where can I find the markings to buy an analogue?
The markings are applied to the top or side of the plastic relay housing. Usually this is a series of letters and numbers (for example, PTC, R-600a, 1/4 HP). Take a photo of this data before going to the store.