Starting the compressor is the most energy-consuming moment in the refrigerator operating cycle, and this is where starting capacitorplays a key role. Without this small component, the engine simply will not be able to overcome the inertia and start rotating, leaving the chamber without cold. Owners often confuse it with a working capacitor or have no idea of its purpose until the equipment stops turning on.
In this article we will analyze in detail the physical principle of the element’s operation, its place in the electrical circuit and the reasons why it fails. Understanding why do you need a starting capacitor in the refrigeratorwill help you quickly diagnose the problem and avoid costly repairs of the entire compressor unit.
Modern models of household appliances, be it Indesit, Atlant or Beko, use similar starting schemes for asynchronous motors. However, the characteristics of the parts used may vary significantly depending on the power of the motor and the year of manufacture of the device.
The physical principle of operation and the creation of phase shift
An asynchronous motor installed in a compressor, by its nature, does not have an initial torque. If you apply voltage directly to it, the rotor will only hum, remaining motionless. To create an initial push, it is necessary to form a rotating magnetic field, which is the main task of the starting winding capacitor.
The capacitor in the circuit creates a phase shift between the currents of the working and starting windings. Ideally, this shift should be 90 degrees, which allows for maximum starting torque. As soon as the rotor reaches about 75% of the rated speed, the starting winding is turned off using the starting relay, and the motor continues to operate on the working winding.
⚠️ Attention: Using a capacitor with an unsuitable capacity may lead to overheating of the windings or the inability to start the motor under load. Always check the markings of the part before replacing.
The process of creating a phase shift occurs instantly at the moment of switching on. It is in these first fractions of a second that a current that significantly exceeds the operating current passes through the capacitor. Therefore starting capacitors they are manufactured with the expectation of short-term but powerful electrical loads.
It is worth noting that in older models of refrigerators circuits without capacitors could be used, where starting was ensured only by the difference in winding resistance, but such motors had low efficiency and high noise levels when start.
Why exactly 90 degrees?
In the theory of electrical machines, a phase shift of 90 degrees provides a circular magnetic field, which creates a uniform torque. When deviating from this value, the field becomes elliptical, which reduces starting efficiency and increases vibrations.
Differences between starting and working capacitors
A common mistake during repairs is trying to replace the starting element with a working one or vice versa. These parts, despite their external similarity (often cylindrical or rectangular housings), have fundamentally different characteristics and purposes in the circuit.
Starting capacitor is included in the circuit only for the time the engine starts (usually 1-3 seconds). Its main characteristic is its ability to withstand short-term surges in voltage and current. After launch, it is completely excluded from operation. The working capacitor is constantly in the circuit and serves to correct the power factor and improve engine operation in normal mode.
If your refrigerator has a two-phase motor, then there may be both a starting and a working capacitance. In modern compressors, a circuit is more often used where the starting capacitor is paired with a starting relay, and the working one may be absent altogether or be built into the circuit differently.
You can visually distinguish them by marking the capacitance (uF) and operating voltage (V). Start-up models often have lower capacity than run-time models in some circuits, but higher peak load requirements. However, you cannot rely only on appearance - you need to check with technical documentation.
Symptoms of a faulty starting device
You can understand that the problem lies in the starting system by the characteristic signs. Most often, the refrigerator stops freezing, but continues to consume electricity and make sounds.
The first and most obvious symptom is compressor humming. The engine tries to start, hums for a few seconds, after which the relay clicks and the hum stops. After some time, the cycle repeats. This indicates that the starting impulse is too weak or absent.
The second sign is complete silence of the refrigerator when the light in the chamber is on. If the compressor is cold and does not vibrate, the starting winding may have burned out or the capacitor itself has lost its capacity completely.
- 🔊 The compressor hums for 5-10 seconds, then clicks and goes silent - a classic sign of the engine’s inability to reach operating speed.
- 🔥 Strong heating of the compressor housing at the bottom parts, although there is no cold in the chambers - the motor is operating in short circuit or overload mode.
- ⚡ Knocking out plugs or tripping the RCD when trying to start the refrigerator - breakdown of the capacitor to the housing or short circuit in the circuit.
- 📉 Unstable operation: the refrigerator turns on only after a long period of inactivity or manual push (occurs in older models).
It is important not to ignore these signals. Long-term operation of the engine in the “humming” mode without rotation of the rotor leads to overheating and interturn short circuit of the windings, which makes repairs economically unfeasible.
Diagnostics and testing with a multimeter
To accurately determine the fault, you need to remove the part from the refrigerator and test measurements. Before starting any work, be sure disconnect the refrigeratorto remove the plug from the socket. Access to the condenser is usually located in the lower rear part of the unit, next to the compressor.
First, a visual inspection is carried out. Swelling of the housing, electrolyte leaks, blackening of contacts or a burning smell clearly indicate the need for replacement. If there are no external defects, the multimeter comes into play.
Switch the device to the mode of measuring resistance (Ohm) or checking diodes. Touch the leads of the capacitor with the probes. If the capacitance is working properly, the needle of the analog device should deflect and slowly return back. On a digital multimeter in continuity mode, the resistance value should increase from several hundred Ohms to infinity.
Multimeter mode: Resistance (200 kOhm or 2 MOhm)Normal reaction: Resistance increases from 0 to ∞
Fault: Resistance equals 0 (short circuit) or immediately ∞ (break)
It is also worth checking the capacitor for breakdown. To do this, switch the multimeter to the mode for measuring constant voltage or resistance at the maximum limit. If the device shows a stable low resistance, it means that the dielectric inside is broken, and the part must be disposed of.
☑️ Procedure for checking the capacitor
Table of faults and elimination methods
For convenience To systematize the problems associated with starting the engine, we present the main breakdown scenarios. Remember that replacing a capacitor often requires replacing the start relay as well, since these elements work in tandem and wear out at the same time.
| Symptom | Probable cause | Elimination method | Difficulty |
|---|---|---|---|
| Humming, clicking, startup in 5-10 minutes | Capacitor loss | Replacing the capacitor with a similar one | Low |
| Humming, clicking, starting only by hand | Sticking contacts of the starting relay | Replacing the starting relay | Low |
| Knocks out the machine in the panel | Breakdown of the capacitor on the body | Urgent replacement of the capacitor | Medium |
| Humming, heating, no start | Compressor wedge or winding break | Diagnostics of the compressor, replacement possible | High |
When selecting an analogue for replacement, the key parameter is the capacitance (uF). Deviation within ±5-10% of the nominal value is allowed. The operating voltage of the new capacitor must be equal to or exceed the voltage of the old one (for example, you can set 450V instead of 250V, but not vice versa).
If after replacing the capacitor the situation has not changed, the problem may lie in the compressor itself or in the thermostat, which does not give the command to start.
Rules for selecting and replacing a component
Replacing the starting capacitor is one of the most accessible procedures for a home mechanic, but it requires care. The main rule: parameters of the new part must meet the requirements of the refrigerator manufacturer.
Pay attention to the type of capacitor. Refrigerators use non-polar electrolytic or film capacitors designed to operate in alternating current (AC) circuits. Installing a polarized capacitor (DC) will cause it to explode when turned on.
⚠️ Attention: Before connecting a new capacitor, be sure to discharge it if it was already in use, or make sure that there is no residual voltage in the circuit. Short-circuiting the terminals with a metal tool (a screwdriver with an insulated handle) is safe for a working part, but dangerous in the event of a breakdown.
When installing, try to place the new capacitor in the same position as the old one so that vibrations do not damage the contacts. If the original mount is burnt, use plastic clamps or heat-resistant glue, but do not glue the part directly to the hot compressor. Some refrigerator models may have a specific shape of capacitors. In this case, you can use universal models, securing them next to the relay if they do not fit into the standard casing.
Some refrigerator models LG or Samsung may have a specific shape of capacitors. In this case, you can use universal models, securing them next to the relay if they do not fit into the standard casing.
Is it possible to start a refrigerator without a starting capacitor?
Theoretically, some low-power motors can start without a capacitor if you turn the shaft manually, but they will operate unstably, with low efficiency and high energy consumption. This is unacceptable for a refrigerator, as it will lead to rapid failure of the compressor.
How often should the starting capacitor be changed?
The service life of a high-quality capacitor is 10-15 years. However, in conditions of unstable voltage in the network or frequent power surges, the part may require replacement after 5-7 years of operation.
Does room temperature affect the operation of the capacitor?
Yes, extremely high temperatures (above +50°C) can accelerate the drying of the electrolyte inside the capacitor, reducing its capacity. Low temperatures also affect dielectric properties, so it is important to use parts with a suitable temperature range.
Why does the compressor hum, but does not start after replacing the capacitor?
If the new capacitor is working and correctly connected, but the engine does not start, the mechanical part of the compressor (piston group) may have jammed or an interturn short circuit has occurred in motor windings.