The situation when the refrigerator stops cooling, but the food inside is already defrosting, always takes you by surprise. The first thing that unit owners usually blame is the thermostat or lack of electricity, but most often the problem lies in the heart of the system - the compressor. It is this unit that is responsible for the circulation of the refrigerant, and if it fails, the cold is simply not generated. Diagnostics of this element often requires removing the start-protection relay, since it is through it that power is supplied to the engine.
Many old-school craftsmen and modern engineers agree that testing directly, bypassing standard protection systems, is the most reliable way to identify a malfunction. This allows you to understand whether the motor itself is alive, or whether the problem lies in the control electronics. However, you should understand that this method requires strict adherence to safety precautions, since you are working with high voltage and open contacts.
In this article we will analyze in detail the algorithm of actions, the necessary tools and the physical principles of operation of the electric motor, so that you can independently carry out initial diagnostics. We will not rely on guesswork, but use precise measurements and logical analysis of the behavior of the unit. Safety when carrying out such work is priority number one, so it is absolutely impossible to ignore the rules for working with electrical appliances.
Operation principle and role of the starting relay
In order to correctly diagnose a malfunction, you need to have a clear understanding of exactly how the asynchronous motorinstalled in your refrigerator works. The compressor has two main windings: starting and working. In normal operation, the relay supplies current to both windings only at the moment of start, and then turns off the starting one, leaving only the main one to work. If this mechanism is broken, the motor either will not start or will hum but not rotate.
A time relay or thermal protection relay performs the function of a guard. They monitor starting current and temperature. If the motor does not start in a split second, the current increases and the relay opens the circuit, preventing the windings from burning out. Checking a compressor without a relay actually means that we take on the function of this guard, applying voltage manually and monitoring the starting process.
There is a common It is a misconception that the absence of a relay click always indicates that it is broken. In fact, if the motor windings have a turn-to-turn short or open circuit, the relay may not operate at all or may operate instantly. That is why excluding this element from the circuit during diagnostics gives a clearer picture of the condition of the motor itself.
⚠️ Attention: When voltage is applied directly to the compressor contacts, the thermal protection disappears. If the motor seizes or the current increases to critical levels, the windings can burn out in a matter of seconds. Keep your finger on the plug or machine to instantly de-energize the system when smoke or a strong burning smell appears.
Required tools and precautions
Before proceeding with disassembly and measurements, you must prepare the workplace and tools. You don't need a complex industrial machine, but a basic electrician's kit is a must. The quality of diagnostics directly depends on the accuracy of instrument readings and your attention to detail.
The main tool will be a multimeter. It is advisable to use a digital device with the ability to test and measure resistance over a wide range. You will also need screwdrivers to remove the compressor casing, pliers and, possibly, electrical tape for temporary insulation of contacts.
☑️ Preparation for diagnostics
Pay special attention to visual inspection. If traces of oil are visible on the compressor, this may indicate a seal failure, which makes further diagnostics pointless - such a unit requires replacement. Also check the integrity of the wires going to the relay.
- 🛠️ Multimeter — to measure the resistance of the windings and check for breakdown.
- 🔌 Insulated wires with clamps —for safe voltage supply.
- 🧤 Dielectric gloves —additional protection against electric shock.
- 🔦 Flashlight —for illuminating hard-to-reach places in the compressor niche.
Visual diagnostics and access to contacts
The process begins with providing access to the technical area. In most refrigerator models, the compressor is located at the lower rear of the cabinet. It is covered with a metal or plastic casing, which must be carefully removed. Do not use excessive force to avoid damaging the tubes or wires.
After removing the casing, you will see a black barrel-shaped unit with copper tubes. A plastic box is usually attached to its end - this is the starting relay along with thermal protection. This is what we have to dismantle. Before doing this, be sure to take a photo of the connection diagram so that you don’t confuse anything later.
Carefully disconnect the relay connector from the compressor contacts. Sometimes they can become oxidized or become sticky. In such cases, you can slightly rock the connector from side to side, but this must be done very carefully so as not to break the plastic clips. Under the connector you will see three contacts arranged in a triangle.
Features of the contact arrangement
The contacts on the compressor are not randomly located. Typically, the top contact (top of the triangle) is the common wire, the bottom left is the starting winding, and the bottom right is the working winding. However, the circuit may differ for different manufacturers (Indesit, LG, Bosch), so it is better to check the technical documentation of the specific model.
Inspect the contacts themselves on the compressor. If they are blackened, melted or have a greenish oxide coating, they must be cleaned with fine sandpaper before taking measurements. Poor contact can distort resistance readings, creating the illusion of a break.
Method of checking windings with a multimeter
The most reliable way to understand the condition of the motor is to measure the resistance of its windings. Switch the multimeter to resistance (Ohm) measurement mode, selecting a limit of 2 kOhm. First, check each contact for breakdown to the housing. Touch one probe to any contact, and the other to the copper tube or unpainted part of the case.
If the device shows infinity (one in the most significant digit or the OL symbol), then the insulation is intact. If you see any resistance values, this indicates a breakdown on the body. Such a compressor cannot be operated, it is mortally dangerous.
Next we move on to measurements between the contacts themselves. You will get three values: between the top and left, the top and right, and also between the two bottom. The sum of the resistances of the two smaller arms should be equal to the resistance of the longest arm (between the extreme contacts). This is the basic law of physics for connecting windings in series.
| Measuring parameter | Normal value | What does deviation mean |
|---|---|---|
| Working winding resistance | 10–30 Ohm | Open (infinity) or short circuit (close to 0) |
| Starting winding resistance | 20–50 Ohm | Starting winding burnout |
| Resistance between the extreme contacts | Sum of the other two | Error in measurements or complex malfunction |
| Breakdown to the body | Infinity (∞) | Short circuit, risk of electric shock |
It is important to note that resistance values may vary depending on the power and model of the compressor. For example, inverter models resistance may be different, since they use a different starting technology. However, the principle of maintaining the proportions between the windings remains unchanged.
Direct engine start: algorithm of actions
If measurements with a multimeter show that the windings are intact and there is no breakdown on the housing, you can proceed to the most important stage - trying to start. To do this, you will need to apply 220 Volts directly to the contacts. Since the starting winding is needed only for starting, the connection diagram will be specific.
You will need two wires. One wire (working) is connected to the common terminal and the working winding terminal. The second wire (starting) is connected to the common terminal and the starting winding terminal, but only for a split second. In reality, they often use a button or simply briefly touch the contact, simulating the operation of a relay.
⚠️ Attention: Do not leave the starting winding energized for more than 1-2 seconds! It is designed for short-term operation and will burn out if connected for a long time, after which the compressor will become unsuitable for repair.
The procedure is as follows: connect the working wire to the network (being careful!), then short-circuit the starting winding circuit. If the motor is working properly, you will hear a confident hum and feel vibration. The output tubes should begin to heat up, and the input tubes should begin to cool (although to check the functionality, simply the fact of starting is enough).
If a hum is heard when voltage is applied, but the shaft does not rotate, and after a couple of seconds the machine knocks out or the protection is triggered, it means the engine is jammed. The mechanical part (piston group) is out of order, and no electrical manipulation will help here.
If the start is successful, let the motor run for a few seconds without load. Pay attention to the nature of the sound: it should be smooth, without knocking, grinding or metallic clanging. Any extraneous noise indicates the destruction of internal mechanical components.
Analysis of results and typical errors
After all the manipulations, it is necessary to draw conclusions. If the compressor starts, runs smoothly and builds pressure (check with your finger on the outlet tube, but be careful, you can get burned), then the problem was in the relay or thermal protection. Replacing them will solve the problem.
If the measurements show a break, or the motor hums and does not start even with a direct current supply, then the compressor must be replaced. As a rule, sealed units of household refrigerators cannot be repaired, since it is necessary to open the case and evacuate the system.
A common mistake in diagnostics is ignoring the condition of the capacitor (if it is in the circuit) or incorrectly identifying the contacts. Also, beginners often confuse the starting and working windings, applying the main voltage to the wrong coil, which leads to instant failure.
- ❌ Error: An attempt to start a three-phase motor from a single-phase network without a capacitor (found in industrial refrigerators).
- ❌ Error: Using wires that are too small sections that heat up and distort the results.
- ✅ Correct: Strictly following the diagram and using a working measuring instrument.
It is also worth considering that in modern refrigerators with a system No Frost and electronic control, the start of the compressor can be controlled by a control board. If the board “sees” a malfunction of the sensors, it simply will not send a signal to the relay, even if the relay itself and the motor are working.
⚠️ Attention: In models with inverter compressors, direct starting from a 220V network is impossible! They are powered by direct current through a special conversion unit. An attempt to apply voltage directly to them will lead to irreversible damage to the electronics.
Frequently asked questions (FAQ)
Is it possible to test a compressor without a multimeter?
Accurately determine the condition of the windings without a device it is impossible. However, if, with a direct connection (in compliance with all safety measures), the motor starts and runs, then the electrical part is intact. But this method is risky and does not provide information about the insulation resistance.
Why does the compressor hum but does not start?
This is a classic sign of a jammed mechanical part (piston group) or a faulty starting winding/relay. The motor tries to turn the shaft, but physically cannot do this due to lack of lubrication, wear or hydraulic shock with freon.
Is it dangerous to change the compressor yourself?
Yes, very much so. Replacement requires not only a new unit, but also professional equipment: a vacuum pump, a pressure gauge station, a burner and refrigerant. Without creating a vacuum in the system, the refrigerator will not work, and moisture inside will lead to rapid breakdown.
How long does a compressor last on average?
The service life of a high-quality compressor is 10-15 years or more. However, frequent power surges in the network, overheating (due to dust on the condenser) or incorrect installation of the refrigerator (too close to the wall) can reduce this period by half.