Has the refrigerator stopped freezing, but has room temperature set inside? Often the cause of such a malfunction is compressor, which is the heart of the entire refrigeration system. However, before calling a technician or buying new equipment, it is worth carrying out an initial diagnosis to ensure the nature of the breakdown. Owners often confuse a motor failure with a faulty thermostat, start relay, or refrigerant leak, which leads to unnecessary expenses.
In this article, we will look at how to check a refrigerator compressor motor using basic tools and a multimeter. You will learn how to distinguish a mechanical blockage from an electrical breakdown, and you will understand whether it is worth repairing the unit or whether it is easier to replace it. Critical important: if during a visual inspection you find swelling of the compressor housing or traces of oil under it, further self-diagnosis can be dangerous.
First, you need to localize the source of the problem. If the refrigerator hums but does not start, or starts for a couple of seconds and immediately clicks when it turns off, these are classic symptoms of problems with the starter mechanism or the motor itself. In situations where the equipment is completely silent and does not make any sounds, checking the electrical circuit becomes the first step to restoring the cold.
Primary visual diagnostics and preparation
Before picking up measuring instruments, it is necessary to conduct a thorough external inspection. Unplug the refrigerator and move it away from the wall to gain access to the back panel. Remove the protective casing covering the compressor group and carefully examine the condition of the unit itself and adjacent parts. Look for traces of soot, melted insulation or oily smudges, which may indicate a breakdown or leakage.
Pay special attention to the start relay, which is usually mounted on the side of the compressor housing. If traces of thermal effects are visible on the plastic or a burning smell is felt, then the problem probably lies in this unit, and not in the motor itself. In some cases, it is enough to replace the relay to motor-compressor work normally again.
⚠️ Attention: It is strictly forbidden to carry out any manipulations with electrical components while the refrigerator is connected to the network. The risk of electric shock when working with 220V voltage is extremely high.
Also check the integrity of the supply wires. Often rodents or mechanical damage during the cleaning process disrupt the insulation, which leads to a short circuit. If visually normal, you can proceed to a deeper check using tools.
Necessary tools for testing
For high-quality diagnostics, you will need a minimum set of tools that most home craftsmen can find. The main device will be multimeter (tester), which allows you to measure the resistance of the windings and check for a short circuit to the housing. Without this device, accurate diagnostics of the electrical part of the engine is impossible.
In addition to the multimeter, prepare screwdrivers for removing the casing and terminals, as well as pliers. If you plan to test “directly” (which will be discussed below), you will need a piece of wire with a plug and, possibly, a working start relay for a test start.
- 🔌 Multimeter (digital or analog) for measuring resistance.
- 🔧 Set of screwdrivers (phillips and flat) for dismantling protection.
- 🧤 Dielectric gloves for safety.
- 💡 Incandescent lamp (optional) for checking the circuit.
Make sure that the multimeter probes are in good condition and their wires do not have insulation damage. Before starting measurements, always check the functionality of the device itself by connecting the probes to each other - the screen should display a value close to zero.
Checking the integrity of the windings with a multimeter
The most reliable way to determine the condition of the engine is to test the continuity of the windings. To do this, you need to remove the start relay and the protective contact cover on the compressor. You will see three pins forming a triangle. These terminals correspond to the starting winding, working winding and common wire.
Switch the multimeter to resistance measurement mode (Ohm) to the 2 kOhm limit. First, find the common wire: measure the resistance between all pairs of contacts. The pair with the least resistance is the working and starting windings, and the remaining third contact is common wire. Typically, the resistance between the working and starting windings is the sum of the resistances of each of them relative to the common wire.
Normal resistance values for a working compressor of a domestic refrigerator vary within the following limits:
| Winding type | Normal resistance (Ohm) | Failure sign |
|---|---|---|
| Working winding | 10 - 30 Ohm | Open (infinity) or short circuit (zero) |
| Starting winding | 20 - 50 Ohm | Open or short circuit |
| Case resistance | Infinity (∞) | Any value indicates breakdown |
If the device shows a unit or an infinity symbol on any of the measurements between the terminals, this means open circuit. In this case, the engine burns out and cannot be restored at home. If the resistance is close to zero, it means that an interturn short circuit has occurred.
Diagnostics of breakdown on the housing
One of the most dangerous faults is breakdown of the winding insulation on the metal housing of the compressor. This not only disables the appliance, but also creates a risk of electric shock when touching metal parts of the refrigerator. You can also check this parameter using a multimeter.
Set the tester switch to the resistance measurement mode to the maximum limit (usually 2 MOhm or 20 MOhm). Press one probe to the cleaned area on the compressor housing (where there is no paint or varnish), and with the second one, touch all three motor contacts one by one. A working motor will show infinite resistance.
⚠️ Attention: If the multimeter shows at least some resistance between the windings and the body, it is prohibited to operate such a refrigerator. Even if it works after replacing the relay, the risk of electric shock remains critical.
Sometimes a breakdown occurs only under voltage. In such cases, the multimeter may not show anything, but when power is applied, it will knock out the machine in the panel or trigger the RCD. For accurate diagnostics in difficult cases, professionals use Meggerwhich supplies high voltage to check the insulation, but in everyday life a high-quality multimeter is sufficient.
Checking the starting relay and thermal relay
Often the motor itself is fine, but does not start due to a faulty start relay. This small block is responsible for sending an impulse to the starting winding. To check it, carefully remove the relay from the compressor contacts. Visually inspect the insides: if a burnt coil or melted contacts are visible inside, the part requires replacement.
Check the relay for resistance. Depending on the design (electromagnetic or posistor), the technique may differ. The posistor must have a resistance within tens of ohms. If the device shows zero or infinity, the relay is faulty. Also check the thermal protection relay, which is often built into the design of the starter.
How does a posistor work?
A posistor is a ceramic element that, when heated by current, sharply increases its resistance, opening the circuit of the starting winding. If it is “broken,” current continues to flow to the starting winding, causing humming and overheating.
Replacing the starting relay is an inexpensive and simple procedure. The main thing is to choose an analogue with the same characteristics and type of connection. An incorrectly selected relay may not start the engine or cause it to burn out quickly.
Direct start of the compressor (bypass test)
If all previous tests are successful, but the refrigerator does not work, you can try to start the compressor directly, bypassing the standard relay. This method allows you to finally verify the performance of the engine. To do this, you will need a piece of wire with a plug and, preferably, a working starting relay or a button for short-term voltage supply.
The connection diagram is simple: the phase wire from the plug is connected to one of the outer contacts (usually the working winding), and the zero wire is connected to the common one. To start, you need to briefly apply voltage to the starting winding. Be careful: the motor shaft will begin to rotate instantly.
- ⚡ Connect the wires to the compressor contacts according to the diagram.
- 🔋 Plug the plug into the socket (being careful!).
- 🔊 Listen to the sound: a steady hum indicates condition.
- 🛑 Turn off the power immediately if sparks or smells appear.
If the motor starts and runs smoothly, the problem was in the start relay or thermostat. If a hum is heard without the shaft rotating or the protection is triggered, the mechanical part of the compressor may be jammed. In the latter case, resuscitating the unit is extremely difficult and often economically unfeasible.
☑️ Compressor diagnostics
Mechanical faults and jamming
Sometimes the electrical part is completely intact, but the compressor does not start due to mechanical jamming of the piston group. This can happen due to exhaustion, lack of lubrication, or moisture entering the system. The symptom is often a characteristic metallic clang or buzz when trying to start, after which the thermal protection is triggered.
There is a “wedging” method, when increased voltage is applied to the contacts or a sharp start is made to tear the pistons out of place. However, this method is risky and can completely kill the compressor. If you do not have experience, it is better not to experiment.
⚠️ Attention: You cannot open the compressor housing to repair the mechanical part at home. This requires evacuation of the system, oil change and precision soldering, which is only possible in a specialized workshop.
If jamming is diagnosed, the only way out is to replace the compressor with a new one. When installing a new unit, it is imperative to replace the filter drier and evacuate the circuit, otherwise the new part will quickly fail.
Frequently asked questions (FAQ)
Is it possible to repair a burnt-out compressor?
In a regular workshop or at home - no. Rewinding windings requires special equipment and sealing. It is easier and more reliable to replace the entire unit with a new one.
Why is the compressor hot to the touch?
The operating temperature of the compressor can reach 60-90 degrees, which is normal. However, if it is hot to such an extent that you cannot touch it, or works without interruption, this is a sign of a malfunction of the thermostat or a freon leak.
What resistance should a working compressor have?
The total resistance between the starting and operating windings is usually from 30 to 80 Ohms, depending on the power and engine model. The main thing is the absence of short circuits and breaks.
Is it possible to replace the compressor with an analogue from another brand?
Yes, if the overall dimensions, type of refrigerant, power and performance are the same. It is also important to take into account the type of oil and the requirements for the starting device.