A sudden stop of the refrigeration chamber or an uncharacteristic hum of the unit often makes the owner think about calling a technician, but initial diagnostics can be performed independently using a simple measuring device. Multimeter (or tester) is a universal tool that allows you to determine the integrity of electrical circuits, the presence of voltage and the correct operation of key components without deep intervention in the system. Understanding the operating principles of compressor and the defrost system will help save time and money by eliminating simple faults such as a blown fuse or broken wire.
Before taking active steps, you must ensure complete safety by turning off equipment from the mains. Any manipulation of internal components requires removal of the back panel and access to electrical contacts, which should not be done under voltage. In this article, we will analyze a step-by-step algorithm for checking the main elements, provide reference resistance values and point out the nuances that beginners often miss when working with ohmmeter.
Equipment preparation and safety measures
For high-quality diagnostics, you will need a digital multimeter capable of measuring resistance (Ohm) and checking circuit integrity (continuity mode). Analog dial gauges are also suitable, but a digital screen is more convenient for reading precise values. Before starting work, make sure that the device is working: connect the probes to each other - zeros should appear on the screen or a sound signal should sound indicating contact.
Access to the electrical part of the refrigerator is usually located at the back, in the lower part of the case, where the compressor unit is located. Attention! ⚠️ If you see melted insulation, traces of burning or you smell the smell of burnt plastic, it is dangerous to carry out further diagnostics without experience - it is better to immediately contact a service center.
Remove the protective cover of the compressor by unscrewing the fastening screws. You will have a view of the start-up relay, capacitor and motor terminals. All further measurements are made exclusively on a de-energized unit. Even residual voltage in capacitors can be unpleasant, so after unplugging from the outlet it is recommended to wait 2-3 minutes.
☑️ Safety before checking
Diagnostics of the refrigerator compressor
The heart of the refrigeration unit is the compressor, and it is its testing that is most often of interest to equipment owners. The engine has three terminals, closed by a contact group under the starting relay. To get to them, you need to carefully remove the relay and starting capacitor. On the motor body you will see three contacts, often designated by the letters C (Common - common), S (Start - starting winding) and R (Run - working winding).
Switch the multimeter to resistance measurement mode (limit 2 kOhm or 200 Ohm). Measure the resistance between each pair of contacts. Normal values for a working compressor vary depending on the power of the model Indesit, Atlant or LG, but the general pattern remains the same: the resistance of the starting winding is always higher than the working winding. The sum of the resistances of the two windings should be equal to the resistance between the common contact and the other pair.
Table of typical winding resistance values
For low-power compressors (up to 100 W), the resistance of the working winding is 10-15 Ohms, the starting winding is 25-35 Ohms. For powerful inverter models, the values may be lower, about 5-8 ohms. If the device shows infinity (open) or zero (short circuit), the motor is faulty and requires replacement. It is also important to check the “breakdown on the body”: one probe is placed on any contact, the second - on the cleaned part of the body (where there is no paint). The device should show infinity. Any resistance value indicates an insulation failure, which is fatal when turned on.
It is important to understand that even if the windings are intact, the compressor may not start due to a jammed mechanical part or a faulty start relay. However, an electrical test with a multimeter is the first and mandatory stage. Key conclusion: If the resistance between any contact and the housing is not infinite, the operation of such a refrigerator is prohibited.
Checking the thermostat and temperature sensors
Thermostat (thermostat) is responsible for turning the compressor on and off depending on the temperature in the chamber. In modern models with the system No Frost this function is performed by electronic sensors (thermistors). The easiest way to check a mechanical thermostat is to remove it, set the regulator to the “maximum cold” position and test the contacts. The device should show zero (short circuit).
If you turn the knob to the “off” or minimum cold position, the circuit should break and the multimeter will show one (infinity). For a more accurate check, the mechanics can be immersed in cold water with ice for several minutes - the contacts should click and open. Electronic sensors are checked by measuring their resistance at room temperature and comparing the readings with a table of values for a specific model.
Attention! ⚠️ When replacing a thermostat, it is important not to confuse the length of the capillary tube. A tube that is too long may touch the evaporator in an unintended place, which will lead to incorrect operation of the refrigerator. Use original spare parts or complete analogues in geometric dimensions.
A common mistake is to ignore the condition of the thermostat contacts. Even if they ring, deposits on the surface can create high contact resistance, causing the relay to not operate correctly. Visually inspect the group of contacts: they should be clean, without black spots of oxidation.
Testing the defrost heating element and timer
In refrigerators with a system No Frost a working defrost system is critically important, the central element of which is the heating element (tubular electric heater). It is located on the evaporator, hidden behind a plastic panel inside the freezer. To check the heating element, you need to get to its contacts and measure the resistance. A working heating element has a resistance in the range from 200 to 500 Ohms, depending on the power.
If the multimeter shows a break (one on the screen), the heating element has burned out and requires replacement. If the resistance is close to zero, a short circuit has occurred, which usually leads to knocking out the plugs in the apartment when you try to turn it on. Also, be sure to check the heating element for breakdown of the housing by applying one probe to the contact and the second to the metal tube of the heater - the device should be silent.
| Element | Normal resistance | Symptom of malfunction | Action |
|---|---|---|---|
| Defrost heating element | 200 - 500 Ohm | Infinity or 0 Ohm | Replacing the heating element |
| Thermostat (on) | 0 Ohm (Short circuit) | Infinity | Replacing the thermostat |
| Compressor (working winding) | 10 - 30 Ohm | Deviation >20% | Engine diagnostics |
| Defrost fuse | 0 Ohm | Infinity | Replacement fuse |
The defrost timer (or electronic control module) also needs to be checked, although it is more difficult to ring it completely. In mechanical timers, you can check the integrity of the contacts in various positions by turning the rod with a screwdriver. If the contacts do not switch or the resistance is high, the entire assembly is replaced.
Checking the start relay and capacitor
The starting relay is an electromagnetic switch that supplies an impulse to the compressor starting winding. Inside the housing there is a coil and a movable core with contacts. When testing the main circuit (input-output), there should be resistance.