Start compressor is the most critical moment in the operation of a refrigeration unit, requiring an instant supply of energy to create torque. It is this process that is responsible for the combination of the starting relay and capacitor, which often fail after power surges in the network. When the refrigerator stops starting or makes a characteristic humming sound, followed by a click and silence, the problem most often lies in the starting circuit.
Restoring the functionality of the refrigerator by replacing or reconnecting the capacitor is a task accessible to a home handyman with basic skills in working with electrician However, electric current in combination with refrigerant under pressure requires strict adherence safety precautions and precision of actions. An installation error can lead to combustion of the motor windings or complete failure of the unit, so the procedure must be approached with full responsibility and understanding of the physics of the process.
In this article we will analyze in detail the design of the starting unit, consider the differences between inductive and capacitive starting circuits, and also provide a step-by-step algorithm of actions. You will learn how to visually identify a malfunction, what tools are needed for the job, and how to avoid common mistakes that beginners make during diagnosis system.
The principle of operation of the starting connection of the relay and capacitor
Single-phase motors installed in household refrigerators are not able to independently start rotating the rotor, since the magnetic field of one winding does not create the necessary torque. To start, an auxiliary starting winding is used, which is switched on only for a short time. This process is controlled by starting relaywhich opens the starting winding circuit immediately after the engine reaches about 75% of the rated rotation speed.
The capacitor in this system plays the role of a phase shifter, creating an artificial phase shift of the current in the starting winding relative to working This allows the formation of a rotating magnetic field necessary to start the rotor. Depending on the design of the refrigerator, the capacitor can be built directly into the relay housing or connected to it with a separate wire. The capacitance of the element is selected strictly individually by the manufacturer for the characteristics of motor-compressor.
⚠️ Attention: Using a capacitor with an unsuitable capacitance (for example, too large) will lead to overheating of the starting winding and may cause a fire, and too small a capacitance will not allow the compressor to start under load.
There is two main types of connection diagrams: with a starting capacitor, which works only at the moment of start, and with a working capacitor, which remains in the circuit constantly. Modern refrigerators most often use combined circuits or electronically controlled systems, but the principle of the need for a phase shift remains fundamental. Understanding exactly what type of circuit is used in your unit is critical before starting repairs.
Diagnostics of faults before replacement
Before you start dismantling parts, you need to make sure that the problem lies precisely in the starting group. Often, symptoms of a capacitor or relay malfunction are disguised as a breakdown of the compressor itself or a problem with thermostat. Primary diagnostics begins with a visual inspection: if swelling, electrolyte leaks or traces of burning are visible on the capacitor, its replacement is mandatory.
For a more accurate check, you will need a multimeter. The capacitor must have a certain resistance, which gradually increases when the probes are connected. If the device shows zero or infinity immediately, the element is faulty. You should also check the relay contacts for oxidation or burning, since poor contact can imitate malfunction the entire starting system.
Sometimes the cause of the failure is not the electrical part, but the mechanical jamming of the compressor rotor. In this case, even a working capacitor will not be able to start the engine, but will only hum and heat up. To exclude this option, you can briefly apply voltage to the starting winding manually (using the “push” method), but this should only be done by experienced craftsmen who understand the risks short circuit.
- 🔍 Visual inspection for swelling of the capacitor housing or blackening of the relay contacts.
- 🔌 Checking the compressor windings to avoid interturn short circuits or breaks.
- ⚡ Checking the voltage in the network, since low voltage can prevent even a working unit from starting.
Necessary tools and safety measures
Working with The electrical equipment of the refrigerator requires a minimum set of tools, which most home craftsmen can find. The main tool will be a multimeter for testing circuits and measuring capacitance. You will also need pliers with insulated handles, screwdrivers (Phillips and flathead) for removing the casing, and possibly side cutters for cutting wires during installation.
Safety is priority number one. Before starting any work, the refrigerator must be completely disconnected from the electrical network. You cannot rely only on the switch on the case; you must unplug the cord from the outlet. Residual voltage in the capacitors can persist for a long time, so before touching the contacts it is recommended to discharge them by shorting the terminals with an insulated tool or resistor.
When working with the back wall of the refrigerator where the compressor is located, you should be careful with copper tubes refrigerant. They are very thin and easily damaged if handled carelessly. Damage to the circuit will lead to freon leakage, which will require expensive professional repairs involving a vacuum pump and filling equipment.
☑️ Safety check before starting
Connection diagrams: inductive and capacitive starting relay
There are several types of starting relays, and the capacitor connection diagram directly depends on their design. The most common are posistor (induction) relays, where the starting winding is connected through a temperature-sensitive element. In such systems, the capacitor is often connected in parallel with the starting winding and works only in the first seconds. The connection diagram is usually marked on the body of the relay itself or the compressor.
In older models of refrigerators, relays with break contacts controlled by current in the operating winding could be used. Here the capacitor plays a key role in creating the starting pulse. It is important to correctly determine the terminals of the windings on the compressor: working (main) and starting. Usually they are marked with the letters R (Run), S (Start) and C (Common), but in different manufacturers (Indesit, Atlant, Beko) the markings may differ.
| Relay type | Operation principle | Role of the capacitor | Where it is used |
|---|---|---|---|
| Posistor | Opening the circuit when the posistor heats up | Creating a phase shift at start | Modern refrigerators |
| Electromagnetic | Opening by the core when the current increases | Increasing starting torque | Old models (USSR) |
| Thermal | Opening with a bimetallic plate | Stabilization of operation at start-up | Low-power units |
| Electronic | Key (triac) control | Interference filtering or starting | Inverter systems |
When replacing a relay or capacitor, it is extremely important to maintain the original wiring diagram. Even if the new capacitor has the same characteristics, incorrect connection to the relay terminals will cause the element to burn out instantly. Always take a photo of the original connection before disconnecting any contacts.
Step-by-step instructions for connecting a capacitor
The connection process begins with access to the compressor. Remove the rear protective panel of the refrigerator by unscrewing the mounting screws. If the relay and capacitor are covered by a plastic casing, carefully remove it. Memorize or take a photo of exactly how the wires fit into the relay and capacitor terminals. Typically, a capacitor has two or four terminals, but starting circuits use two main ones.
If you are installing a new capacitor, make sure that its capacitance (measured in microfarads, uF) and operating voltage (usually 250V or 450V) meet the requirements specified on the old element's label or in the technical documentation. Connect one wire from the relay to one terminal of the capacitor and the second wire to the other terminal. In some schemes, the capacitor is attached directly to the relay body with special latches.
Sequence of actions:1. Disconnect the old relay from the compressor.
2. Remove the terminals from the old capacitor.
3. Install the new capacitor into the mount.
4. Connect the wires according to the diagram (usually without polarity for alternating current).
5. Place the assembled structure onto the compressor rod until it clicks.
After physically connecting all the elements, reassemble the structure in the reverse order. Make sure that the wires do not touch the hot compressor pipes and are at a safe distance from moving parts (in the case of fans on some models). Securely fasten the casing so that vibration during operation does not break contact.
What to do if the wires are of different colors?
In AC circuits, the polarity of the capacitor connection is usually not important if there is no +/- marking on the housing. However, try to maintain a color scheme of blue to blue, brown to brown to avoid confusion in the future. If the colors do not match, be guided by the connection diagram of a specific relay.
Typical errors and methods for eliminating them
One of the most common mistakes is ignoring the state of the contacts of the relay itself. Even a new capacitor will not help if the contacts inside the relay are oxidized or burnt, creating high contact resistance. As a result, the starting current will be insufficient and the compressor will not be able to turn the shaft. Always evaluate the condition of the entire starting group in the complex.
Another common mistake is using a capacitor with a lower operating voltage than required. If a voltage surge occurs in the circuit, such a capacitor can break through, leading to a short circuit. Always choose an element with a voltage reserve (for example, 450V instead of 250V), this will increase the service life of the part without affecting the operability circuits.
⚠️ Attention: Never leave the capacitor just hanging on the wires without fastening. Vibration of the compressor can lead to wires being torn off and a short circuit to the refrigerator body.
Also, technicians often forget to check the compressor for inter-turn short circuits before installing new parts. If the motor is faulty, it will draw huge current, which will instantly destroy the new capacitor and relay. Therefore, the primary diagnosis motor is a mandatory step that should not be skipped to save time.
- 🛑 Installing a larger capacitor "by eye" will lead to overheating of the windings.
- 🔌 Poor contact in terminal block - will cause sparking and heating.
- 🌡️ Ignoring compressor overheating - may indicate problems with ventilation, not electrical problems.
Is it possible to start a refrigerator without a capacitor?
Theoretically, some powerful engines can start without a capacitor when the shaft is manually cranked, but they will not work normally. Without a capacitor, the necessary phase shift is not created, and the engine either will not start, or will hum and quickly overheat, which will cause the thermal relay to operate or the winding to burn out.
How to determine the capacitance of a burnt capacitor without markings?
If the marking is erased, it is impossible to determine the exact capacitance without a circuit. However, you can focus on the power of the compressor: for low-power (up to 100 W) 6-10 μF is usually used, for medium (100-200 W) - 10-15 μF, for high-power - 16-20 μF. It is best to find the compressor model on the Internet and look at the specification.
Why does a new relay burn out a week after replacement?
This often indicates that the cause of the breakdown was not in the relay itself, but in the compressor (difficult start, jamming) or in unstable network voltage. It is also possible that a relay was installed with incorrect release current characteristics for this type of engine.