The situation when the refrigerator stops turning on, and the cause of the malfunction is a burnt one starting relay, often takes the owner by surprise. In most cases, the compressor is fine, but the lack of a start signal prevents it from starting. Many craftsmen and home craftsmen are looking for a way to temporarily start the unit in order to preserve products or carry out diagnostics, bypassing the standard control unit.
However, it is important to immediately understand: starting a three-pin relay directly is an emergency measure that requires strict adherence to safety precautions. Start protection device it does not just supply current, it opens the starting winding after gaining speed and protects the motor from overheating. Ignoring these functions can lead to the final failure of an expensive compressor or a wiring fire.
In this article we will examine in detail the contact group device, methods of forced starting and the risks associated with such a procedure. You will learn how to identify winding terminals, what tools are required for work, and why long-term use of a refrigerator without standard protection is categorically not recommended by equipment manufacturers.
The principle of operation of the compressor starting mechanism
To successfully start a motor without a standard relay, you must clearly understand how the standard circuit works. A single-phase asynchronous motor installed in household refrigerators has two windings: working and starting. The working winding creates the main magnetic field, and the starting winding is needed only at the moment of start to create torque.
A three-contact relay (often called RTP, R-1 or similar markings) performs two critical functions. Firstly, it supplies voltage to the starting winding at the moment of switching on. Secondly, a thermal relay inside the housing opens the circuit when the current exceeds, protecting the engine from combustion. Without this mechanism, the current in the starting winding will remain constant, which will lead to rapid overheating.
Electromagnetic relay triggered due to the current flowing through the working winding. When the rotor reaches about 75% of the rated speed, the current drops and the relay opens the contacts of the starting winding. Understanding this logic is necessary to manually simulate the startup process.
Why does the relay burn out?
A frequent cause of relay burnout is jamming of the compressor piston group or a drop in voltage in the network. If the motor cannot turn over, the current in the working winding does not drop, the relay contacts stick or overheat, causing a short circuit or open circuit.
Identification of motor contacts and windings
The first step before any intervention in the electrical circuit is to determine the purpose of the compressor terminals. Typically, on the motor body there is a terminal block with three terminals arranged in a triangle. It is important not to confuse them, since applying voltage to the wrong winding will instantly disable the unit.
For an accurate determination, you must use multimeter in resistance measurement mode (Ohms). Remove the terminal box cover and carefully disconnect the old relay wires. Measure the resistance between each pair of contacts. The pair with the least resistance is the run and start windings together, and the common wire will have an average resistance value relative to each of the other two.
- 🔌 Common wire (Common): The contact relative to which the sum of the resistances of the other two gives the maximum value, or the contact that has the least resistance with both others.
- ⚙️ Working winding (Run): It has a lower resistance (usually 10-30 Ohms) and is connected directly to the network.
- 🚀 Start winding: It has a higher resistance (usually 30-60 Ohms) and is connected through a starting device.
Write down the values obtained, as they may be needed to select a relay analogue in the future. In some refrigerator models Indesit or Atlant the terminals may be marked with the letters R, S, C or numbers, but you cannot rely only on the markings without checking with the device.
Direct connection diagram for diagnostics
To temporarily start a refrigerator without a standard relay with three contacts, the direct voltage supply method is used. The essence of the method is to apply a phase to the common wire and the working winding, and then briefly close the starting winding circuit. This simulates the operation of an electromagnetic relay.
You will need a piece of wire with a plug, insulated clamps (“crocodiles”) and, preferably, a non-latching button or toggle switch. Assemble a circuit where one wire from the plug goes to the common contact of the compressor, and the second to the working contact. The starting winding remains free for now or is connected via a button.
⚠️ Attention: Carry out all manipulations with the wires only with the plug pulled out of the socket! Connecting power is possible only at the final stage of the test, when all contacts are securely insulated and fixed.
The algorithm for starting actions is as follows: plug the plug into the network (the engine will hum, but will not start), then briefly (for 1-2 seconds) apply voltage to the starting winding. As soon as the motor picks up speed, the starting winding circuit must be immediately broken. If this is not done, the winding will burn out.
☑️ Safe start of the compressor
Using an external start button
A safer and more controlled option is to use a regular button with normally open contacts (for example, from doorbell or old household appliances). This scheme avoids the risk of “overexposing” the starting winding under voltage, since the operator’s finger acts as a timer.
Assemble a structure where the main power wire goes constantly to the working winding, and the button is connected to a break in the wire going to the starting contact. Pressing the button closes the circuit, the motor starts, releasing it opens it. This is the most reliable way to “revive” the refrigerator before the technician arrives or purchases a new spare part.
It is important to use wires with a cross-section of at least 0.75 mm², since starting currents can reach 10-15 Amperes. Thin wires may melt. Also make sure that the button contacts are designed for a current of at least 16 A, otherwise they may weld to each other.
If the motor does not start after 3-4 attempts, further experiments are useless and dangerous. Most likely, the problem lies in the compressor itself (jamming, interturn short circuit), and not in the relay. Continuing startup attempts can finally finish off the unit.
Table of typical winding resistances
For correct diagnostics, it is useful to check the typical resistance values for various compressor models. Although the exact data depends on the manufacturer (Danfoss, Secop, Atlant), general value ranges will help you understand whether the engine is working properly.
| Compressor type | Operating winding resistance (Ohm) | Resistance starting winding (Ohm) | Total resistance |
|---|---|---|---|
| Low power (up to 100 W) | 15 - 25 | 35 - 50 | Sum of values |
| Medium power (150 W) | 10 - 18 | 25 - 40 | Sum of values |
| High-power (200+ W) | 8 - 14 | 20 - 35 | Sum of values |
| Inverter (not applicable) | N/A | N/A | Controlled by board |
If the multimeter shows infinity (open) or zero (short circuit) on any of the windings, starting by external means is prohibited. Also, the resistance between any terminal and the copper housing of the compressor must be infinite. The presence of conductivity to the housing indicates an insulation breakdown and a mortal danger of electric shock.
Risks and limitations of the direct start method
Operating a refrigerator without a standard start-up relay carries serious risks. The main difference between a homemade circuit and a factory one is the lack of thermal protection. If the compressor jams or overheats, no one will turn off the power, which can lead to fire of the windings or melting of the refrigerator wiring.
In addition, keeping the starting winding energized for a long time (if you do not have time to remove your finger from the button or a homemade relay gets stuck) is guaranteed to burn it out in 5-10 seconds. Restoring a burnt-out starting winding at home is impossible - the entire compressor will need to be replaced.
⚠️ Attention: This method is intended exclusively for short-term diagnostics or emergency switching on for several hours. Constant operation of the refrigerator according to this scheme is unacceptable due to the lack of overload protection.
Another negative factor is the wear of the mechanical part. Improper starting (pulsing too long or too short) creates jerks that can damage valves or crankshaft bearings. Use this method only in extreme cases, when replacing the relay right now is impossible.
Frequently asked questions about starting the compressor
Is it possible to leave the refrigerator running without a relay all the time?
Absolutely not. The absence of a thermal relay will result in the motor burning out during any overload. In addition, the starting winding must be turned off after the start, otherwise it will overheat and short-circuit.
It hums, but does not start - what is the reason?
Most likely, the compressor piston is jammed or the starting winding is faulty. In some cases, hitting the body with a hammer (the “resuscitation” method) helps, but this is a temporary measure. The compressor often needs to be replaced.
Which relay to buy as a replacement?
Look for relays with similar markings (for example, RTK, R-1, R-2). It is important that the rated current and type of compressor (low pressure/high pressure) match. Universal relays are not always suitable.
Is it dangerous to touch the wires while the refrigerator is on?
Yes, it is deadly. Voltage of 220 Volts can be fatal. Make all switches only when the power is off, using an insulated tool.