The situation when the refrigerator suddenly stops cooling, and the food inside quickly deteriorates, is familiar to many. The first suspicion is often a failure compressor, which is the heart of the entire cooling system. However, before calling a technician or buying a new unit, it makes sense to carry out an initial diagnosis in order to understand the scale of the problem.
In this article we will look at how to independently check motor-compressor for performance using available tools. You will learn how to distinguish a breakdown of the engine itself from a malfunction of the starting relay or thermostat, and what measurements need to be taken for an accurate diagnosis.
It is immediately worth noting that working with electrical appliances requires compliance with safety rules. Any manipulations with the electrical part should only be carried out with the device completely disconnected from the network. Ignoring this rule may result in electric shock or further damage to the equipment.
⚠️ Attention: If you smell burning or see obvious traces of melted wiring, it is dangerous to carry out further independent diagnostics. In such cases, it is better to contact professionals.
External inspection and primary signs of malfunction
Before taking up the tools, it is necessary to conduct a visual assessment of the condition of the unit. Often the nature of the malfunction can be determined by the external signs and behavior of the refrigerator when it is turned on. Pay attention to how the compressor compressor behaves when voltage is applied.
If the engine tries to start and makes a characteristic humming sound, but after a few seconds there is a click and it goes silent, this may indicate several problems. Perhaps the piston mechanism itself is jammed, or the start relay has failed. Also, the cause may be an interturn short circuit in the windings.
If the refrigerator is silent and does not make any sounds, the problem may lie in the lack of power at the motor terminals. This happens when the thermostat breaks down or the control circuit breaks. A thorough inspection of the rear of the unit helps to identify visible damage.
Inspect the condenser (grid at the back) for swelling or signs of freon leakage. Although this is not a direct test of the motor, the condition of the system affects the load experienced motor. If the system is sealed, but the compressor does not work, the problem is localized in the electrical part.
Necessary tools for diagnostics
To properly check the refrigerator motor, you will need a minimum set of tools, which can be found in many home craftsmen. The main device will be a multimeter (tester), which allows you to measure resistance and test circuits.
You may also need pliers, screwdrivers to remove the protective casing and, possibly, a separate serviceable starting relay for checking by exclusion. It is important that the multimeter probes are intact and the insulation of the wires is not damaged.
- 🔧 Multimeter —the main device for measuring winding resistance and checking for breakdown.
- 🔧 A set of screwdrivers —for dismantling the protective cover of the compressor and removing the relay.
- 🔧 Pliers —for careful removal of terminals and holders.
- 🔧 Insulating tape —for isolating contacts during a test run.
Before Before starting work, make sure that the refrigerator is unplugged from the power supply for at least 15-20 minutes. This is necessary in order for the capacitors to discharge and cool down unit, which will ensure the safety and accuracy of the readings.
Removal and access to the electrical part
To get to the motor contact group, you need to remove the protective plastic casing located in the lower rear part of the refrigerator. It is usually secured with latches or several screws that can be easily unscrewed.
After removing the cover, you will see a compressor with a black or white plastic block attached to it - this is the start relay along with a thermal protector. It is through this unit that voltage is supplied to the motor windings.
Carefully remove the relay from the compressor contacts. It can be held quite tightly, so be careful not to damage the fragile plastic parts or terminals. On the compressor itself you will see three terminals forming a triangle.
⚠️ Attention: Do not use excessive force when removing the relay. If it cannot be removed by hand, the contacts may be rusty or there is a retaining clip that needs to be released.
Clean the contacts from oxides and dust before taking measurements. An oxidized surface can distort the multimeter readings, leading to an incorrect diagnosis. For cleaning, you can use a regular eraser or alcohol.
Checking the windings with a multimeter
The most informative diagnostic step is measuring the resistance of the windings. The contact field of the compressor usually has markings: C (Common) - common wire, R (Run) - working winding, S (Start) - starting winding. If there are no markings, you need to visually determine the location of the contacts.
Switch the multimeter to the resistance measurement mode (Ohm) to the limit of 200 Ohm or 2 kOhm. First measure the resistance between pairs of contacts. Between the common and working windings, the resistance should be the smallest, between the common and starting windings - average, and between the working and starting windings - the sum of the two previous values.
If the device shows infinity (open) or zero (short circuit) on any of the pairs, this indicates a malfunction of the engine. It is also critically important to check the absence of breakdown on the body.
☑️ Algorithm for checking the windings
To check for breakdown, press one probe to any contact, and the second to a cleaned place on the compressor body (for example, to a copper tube without paint). The device should show infinity. If there is at least some resistance value, then the insulation is broken.
The table below shows approximate resistance values for a working compressor of low and medium power:
| Pair of contacts | Normal resistance (Ohm) | Fault |
|---|---|---|
| Common - Working (C-R) | 10 - 25 Ohm | Open or short circuit |
| Common - Starting (C-S) | 20 - 40 Ohm | Open or short circuit |
| Working - Starting (R-S) | 30 - 60 Ohm | Inconsistency with the amount |
| Any contact - Housing | Infinity (∞) | Breakthrough to the housing |
It is worth remembering that the exact values depend on the model and power of the motor. However, the proportions of resistance (starting is always greater than working) must always be observed. If the data differs greatly from the table, the engine most likely requires replacement.
Diagnostics of the starting relay and thermal protection
Often the compressor itself is working, but the problem lies in the attachments. The starting relay is responsible for briefly supplying voltage to the starting winding, and the thermal relay protects the engine from overheating.
Visually inspect the relay. If traces of burning, melting are visible inside the plastic case, or the smell of burnt plastic is heard, the part is definitely faulty. You can also check the relay with a multimeter in continuity mode.
Principle of operation of the starting relay
When the refrigerator is turned on, current passes through the relay coil, creating a magnetic field that closes the contacts of the starting winding. As the motor picks up speed, the current drops, the magnetic field weakens, and the contacts open. If this mechanism jams, the compressor hums, but does not start.
The thermal relay (tablet) in normal condition should ring (show zero or resistance close to it). If the circuit is broken, the relay must be replaced. This is an inexpensive part that often fails before the motor itself.
When replacing a relay, it is important to choose an analogue that matches the power of your compressor. Using an unsuitable relay can lead to frequent engine shutdowns or, conversely, to its combustion due to lack of protection.
Direct start of the compressor (Test activation)
If the measurements of the windings showed the norm, and the relay is working properly, you can try to start the compressor directly, bypassing the standard automatics of the refrigerator. This method allows you to finally verify the functionality of the motor.
To do this, you will need to assemble a circuit using a working starting relay or a special device for starting. The contacts C i R are connected to the phase and neutral from the network, and the starting winding S is powered through a relay only at the time of start.
⚠️ Attention: Direct starting is dangerous due to electric shock! All contacts must be reliably insulated. Do not touch metal parts of the compressor and wires during operation.
If, when power is applied, the compressor starts and runs confidently, then the problem was in the refrigerator control system (thermostat, control board). If the motor hums, jerks and knocks out the machine, there is a mechanical wedge or an interturn short circuit.
After the test, let the compressor cool. A forced start creates a high load and is not recommended to be repeated immediately. If the engine starts, but does not pump freon (the pipes do not heat up/cool), the valves inside may break.
Frequent diagnostic errors
When independently checking the refrigerator motor, beginners often make mistakes that lead to incorrect conclusions. One of the most common is an attempt to measure resistance without disconnecting the device from the network or without removing the relay.
Another mistake is ignoring the condition of the wiring. If the cable going to the compressor is broken or oxidized, the multimeter will show a break, although the motor itself may be intact. Always check the integrity of the wires to the contact group.
- ❌ Measurement without removing the relay —gives distorted data, since the circuit is closed through the internal contacts of the relay.
- ❌ Ignoring heating —a hot compressor has a different winding resistance, which can be confusing.
- ❌ Incorrect limit on the multimeter —measuring high resistances at the limit of 200 Ohms will show infinity.
Also, do not forget that some modern inverter compressors cannot be checked with a conventional multimeter or started directly. Their diagnosis requires special equipment and knowledge of electronics.
Features of inverter compressors
Unlike classical models, inverter motors are controlled by complex electronics that convert the current. Direct supply of 220V to such a compressor will lead to its instant combustion. First of all, you need to check the control board.
If you doubt your abilities or the instrument readings are contradictory, it is better to stop at the diagnostic stage and invite a specialist. Repairing a refrigerator is a process that requires precision and understanding of the physics of the processes.
FAQ: Frequently asked questions
Is it possible to replace the compressor on a refrigerator yourself?
Theoretically, it is possible, but this requires a vacuum pump, a pressure gauge station and a supply of freon. The process involves soldering copper tubes and vacuuming the system, which is difficult to do at home without experience and equipment.
Why is the compressor hot, but the refrigerator does not freeze?
This may indicate a freon leak or a blockage in the capillary system. The engine is idling, trying to pump coolant that is not in the system or that is not circulating. A breakdown of the valves inside the compressor is also possible.
How much does it cost to replace a compressor?
The cost consists of the price of the unit itself and the work of the technician. On average, replacement costs 40-60% of the cost of a new refrigerator. It is often more economically feasible to buy new equipment, especially if the old one is more than 10 years old.
Does a working compressor hum?
A working motor produces a uniform low-frequency hum. If the sound becomes loud, rattling or metallic, this is a sign of bearing wear or internal mechanical damage.