A sudden stop of refrigeration equipment is always stressful, because food supplies are at risk. Often, equipment owners are faced with a situation where it is warm inside, the lights are on, and the characteristic hum of the engine is not heard. At this moment, the main question arises: has the engine itself failed or is the problem hidden in the control system?
Before calling a technician or buying a new unit, it makes sense to conduct an initial diagnosis. Understanding how to check a refrigerator compressorallows you to weed out simple faults, such as a burnt-out start relay or an open circuit, from more serious problems with the mechanics or electrical of the motor.
In this article we will examine in detail the testing methods sealed unit with various ways. You will learn how to safely measure winding resistance, what to look for during an external inspection and when independent repair becomes dangerous.
Primary diagnostics and visual inspection
Any diagnostics begins with external observation. If the refrigerator has stopped freezing, do not rush to disassemble the back panel. Listen: does the motor make any sounds - clicks, humming, attempts to start. Complete silence often indicates a lack of power or a burnt winding, while a hum followed by a click indicates a jam or problem with the starter.
Inspect the compressor in the rear bay. There should be no traces of oil, severe corrosion or melted wires. If you notice oily smudges in the area of the tubes, this may indicate depressurization of the system, which makes further checking of the electrical system pointless without professional refilling.
⚠️ Attention: Before starting any diagnostic work, be sure to disconnect the refrigerator from the power supply! Working with live electrical components is deadly.
Also check the integrity of the supply cable and plug. Sometimes the reason is simple: the wire is broken or the contacts in the socket are oxidized. Make sure that the thermostat is set to the operating position and not to the “0” or “Off” mode.
Checking the starting relay and thermostat
Before “sinning” on the motor itself, it is necessary to eliminate faults in its starting circuit. Often this is what starting relay fails, preventing the rotor from spinning. It is located on the side or bottom of the compressor and can be easily removed after disconnecting from the mains.
Remove the relay and shake it. If a ringing sound is heard inside, it means the core is broken or the mechanism is destroyed - replacement is required. Visually inspect the contacts: they should be clean, free of carbon deposits and oxides. For a more accurate check, you can “ring” the contacts with a multimeter in ohmmeter mode: when in a vertical position, the resistance should be close to zero, when tilted, there is a break.
Do not forget about thermostat (or the temperature sensor in modern models). If its contacts are open, the start signal simply will not arrive. In older models, you can temporarily short-circuit the wires coming from the thermostat to check whether the motor will start.
Nuances of checking the electronic module
In modern refrigerators with the No Frost system, the start of the compressor is controlled by an electronic control unit. If the relay and motor are working, but there is no start, the problem may be in the “brains” of the refrigerator. It is difficult to check the board yourself without circuit design, but you can visually assess the condition of the board for swollen capacitors or traces of burning.
If, after checking the relay and thermostat, the motor is still silent, we move on to a deeper diagnosis of the unit itself. It is important to understand that the serviceability of external elements does not guarantee the operation of internal mechanics.
Instrumental testing of windings with a multimeter
The most reliable way to understand the condition of the electrical part of the engine is to measure the resistance of the windings. To do this you will need multimeter. Remove the protective casing from the compressor and find the contact group to which the wires are connected.
Carefully remove the terminals and wipe the contacts. There are usually three terminals on the block: two upper and one lower (or arranged in a triangle). You need to find pairs of contacts corresponding to the starting and working windings, as well as the common terminal.
☑️ The order of testing the windings
Normal resistance readings depend on the power of the motor, but usually look like this:
- 🔹 Resistance between the common terminal and the working winding: 10–25 Ohm.
- 🔹 Resistance between the common terminal and the starting winding: 20–40 Ohms (always higher than that of the working winding).
- 🔹 Resistance between the starting and working winding winding: the sum of the two previous values.
If the device shows infinity (open) or zero (short circuit) on any of the windings the compressor is faulty and requires replacement. It is also critical to check the breakdown on the case: press one probe of the multimeter to a cleaned place on the case (where there is no paint), and touch each contact with the other. The device must be silent; any readings indicate an insulation failure.
Table of typical resistance values
For the convenience of comparing the readings of your device with the reference ones, use the table below. Remember that the values may vary slightly depending on the manufacturer and engine temperature.
| Fault type | Multimeter readings | Diagnosis |
|---|---|---|
| Normal | 10-60 Ohm (depending on pairs) | Windings are intact |
| Break | Unit or OL on the display | Open circuit inside |
| Short circuit of turns | Values are much lower than normal | Interturn short circuit |
| Breakthrough to the body | Any value when calling to the body | Dangerous to life |
Please note that turn-to-turn short circuit it is difficult to diagnose with resistance alone, since a difference of several ohms may not be noticeable. However, such a motor will get very hot and knock out the circuit breaker.
Direct start of the compressor without a relay
If the electrical parameters are normal, but the motor does not start, you can try to start it directly, bypassing the starting relay. This method allows you to check the mechanical part and ability of the rotor to rotate. To do this, you will need a piece of wire with a plug and, preferably, a button or switch.
The circuit is simple: we supply the phase from the network to the common contact, and zero to the working winding. The starting winding must be briefly short-circuited with the working winding (or a phase must be applied to it through a capacitor, if required) to create torque.
⚠️ Attention: This method is dangerous! You work with 220V mains voltage on open contacts. Do not touch the wires with your hands while applying power. Use an insulated tool.
If, when power is applied, the motor shaft begins to rotate and a characteristic sound of air intake appears at the inlet pipe, the mechanics are working properly. If a hum is heard, but there is no rotation, or the plugs are knocked out, there is wedge jamming a piston group. In this case, repair is not economically feasible.
Diagnostics of inverter compressors
Modern refrigerators are often equipped inverter motors. Checking them using standard methods (winding continuity testing) is possible, but has limitations. Such motors have three terminals, and the resistance between them is usually the same (symmetrical windings).
The main difference is that the inverter compressor will not start without a control module that converts the current and sets the rotation speed. Direct supply of 220V to the contacts of such a motor will lead to its instant combustion.
Checking the inverter comes down to:
- 🔹 Measuring the resistance of the windings (should be the same between all pairs, usually 5-15 Ohms).
- 🔹 Checking that there is no breakdown on the case.
- 🔹 Visually inspecting the inverter board for swollen capacitors.
If the windings are intact, but the refrigerator does not work, most likely the inverter unit is faulty or complex computer diagnostics of the error is required. You can replace the inverter unit yourself by selecting an analogue based on the refrigerator model.
Frequently asked questions about compressor diagnostics
Is it possible to repair a burnt-out compressor?
At home - no. The sealed case is not intended to be opened. Replacing valves or rewinding an engine requires industrial equipment, evacuation and refrigerant charging. It is easier and more reliable to buy a new unit.
Why is the compressor hot, but the refrigerator does not freeze?
This may indicate a loss of freon due to a leak or a clogged capillary system. The engine idles, trying to pump gas that is not in the circuit, or overcoming the resistance of a blockage. You need to call a technician to find a leak.
How to distinguish fan noise from compressor noise?
In No Frost systems, fans work. If the noise stops when the door is opened (in some models) or is whistling and airy in nature, it is a fan. The compressor emits a low-frequency hum and vibration that radiates into the housing.
Is it worth replacing the compressor on an old refrigerator?
If the refrigerator is more than 10-12 years old, replacing the compressor is often not economically justified. The cost of a new motor and replacement work can be 60-70% of the price of a new budget refrigerator. Old thermal insulators and seals can also be worn out.