The situation when the refrigerator stopped cooling, and the compressor hums, but does not start, or is silent, familiar to many owners of household appliances. Often the cause of failure is the failure of the starting relay, which is responsible for supplying voltage to the starting winding of the engine. In such cases, the master or home craftsman is faced with the question: is it possible to start the motor directly, bypassing the standard circuit, and how to do this safely for the unit and the person. Direct connection requires an understanding of the principles of operation of an asynchronous motor and strict adherence to electrical safety rules.
In this article we will analyze the technical nuances of the work single-phase compressor, contact identification methods and step-by-step forced start algorithm. It is important to understand that starting a compressor without a relay is most often a diagnostic procedure or a temporary solution, since constant operation without protection can lead to overheating and final failure of an expensive unit. We will look at how to determine working and starting windings, what tools are required for work and why in some cases it is categorically impossible to start the motor directly.
Before proceeding with any manipulations with electrical part of the refrigerator, it is necessary to completely disconnect the device. Unplug the power cord from the outlet and make sure there is no voltage at the contacts. Working with 220 volt electricity poses a direct threat to life, so neglecting this rule is unacceptable. All further actions are carried out only with the equipment completely disconnected from the network, and the circuits are checked with a multimeter.
The principle of operation and the role of the starting relay in the circuit
Compressors of household refrigerators, as a rule, are single-phase asynchronous motors with a squirrel-cage rotor. The peculiarity of such motors is that when voltage is applied only to the working winding, the magnetic field does not create the necessary torque to start the rotor from a stationary state. The motor only hums, heats up, but does not rotate. To create a phase shift and starting torque, a second winding is used - starting, which is connected to the network only for a short moment of starting.
The standard starting relay performs the function of an automatic switch for the starting winding. Depending on the design (electromagnetic or posistor), it opens the starting winding circuit immediately after the engine reaches the required speed (approximately 75% of the rated speed). If the relay is faulty and does not open the circuit, the starting winding, which has a thinner wire, quickly burns out. If the relay does not close the circuit at all at start, the compressor will not be able to start.
⚠️ Attention: Continuous operation of the compressor with the starting winding connected (imitation of a closed relay) will lead to rapid overheating and burning of the stator winding within a few minutes or even seconds. A connection diagram without a relay should be used only for a short-term test of the motor's performance.
To force a start, we need to artificially simulate the operation of the relay: apply voltage to the working winding and briefly connect the starting one. In a professional environment, a non-latching button or a special circuit with a capacitor is often used for this, but in domestic conditions they often resort to manual control of the circuit. Understanding which winding is responsible for what is the key to a successful startup.
Identification of contacts and winding continuity
The first stage of preparation for startup is gaining access to the contact group of the compressor. It is usually located at the bottom rear of the refrigerator, covered with a plastic casing. There may be three or four terminals on the terminal block. We need to determine which of them belongs to the working winding, which to the starting winding, and which is common. To do this, you will need a multimeter switched to resistance measurement mode (Ohms).
The dialing process involves measuring the resistance between pairs of contacts. The resistance between the common contact and the working winding is always less than that between the common and the starting winding. This is due to the fact that the working winding is wound with a thicker wire and has fewer turns, therefore, its resistance is lower. The starting winding has a larger number of turns of thin wire, which gives greater resistance.
- 🔍 Find a pair of contacts with the least resistance - this will be a combination of "common" and "working".
- ⚡ Find a pair with the highest resistance - this is "working" and "starting" (the total resistance of the two windings).
- 🔌 The third contact, which remained out of use in the first two measurements, is the “common” one, from which you need to dance further.
If the multimeter shows infinity (break) between any two contacts, this may indicate an internal break in the winding or a tripped thermal protection relay. In some compressor models, thermal protection is built into the housing and has separate terminals. In this case, it is necessary to connect the circuit through these terminals. It is also important to check the resistance between any contact and the copper tube of the housing - there must be a “break” there, otherwise there is a breakdown to the housing, which makes operation dangerous.
⚠️ Attention: If, during testing, you find that the resistance between the windings and the housing is not infinitely high, but is several megaohms or less, using such a compressor is strictly prohibited. This poses a risk of electric shock if you touch the refrigerator body.
Direct connection diagram and action algorithm
After the contacts have been identified, you can proceed to assembling the temporary starting circuit. To do this, you will need a piece of wire with a plug, insulating tape and, preferably, a button with normally open contacts (or just two conductors for manual closing if there is no button, although this is less safe). Connection diagram based on a parallel connection: the phase goes to the common contact, the zero goes to the working winding, and the starting winding is connected in parallel to the working winding through the button only for a moment start.
The algorithm of actions is as follows: one wire from the network (for example, zero) is connected directly to the contact of the working winding. The second wire of the network (phase) is connected to the common contact. The third wire connects the common contact (or phase) with the contact of the starting winding, but a button is placed in the gap of this wire. By pressing the button, we apply voltage to the starting winding, the motor begins to rotate, and the button must be released immediately.
☑️ Check before starting
It is important to observe the time interval. The starting winding should be turned on for only 1-3 seconds. If you keep it on longer, the current in it will increase and it will burn out. If the compressor does not start on the first try, you must wait a few minutes to cool down and equalize the freon pressure in the system before trying again. Frequent starts in a row can damage the compressor valves.
Using a capacitor to facilitate starting
In some cases, especially if the network voltage is low or the compressor is old and runs slowly, direct short-term connection of the starting winding may not be enough. The engine may hum, jerk, but not gain momentum. In such a situation, a starting capacitor is added to the circuit. It creates an additional phase shift, increasing the starting torque.
The capacitor is connected in series with the starting winding. The capacitance of the capacitor is selected experimentally or according to reference data for a specific compressor model, usually in the range from 2 to 5 μF for household refrigerators. It is important to use capacitors designed for a voltage of at least 300-400 volts (preferably 450V), since voltage surges are possible during startup.
| Component type | Purpose in the circuit | Connection time | Risk when error |
|---|---|---|---|
| Working winding | Main rotation of the rotor | Constant | Combustion during overload |
| Starting winding | Creation of starting torque | 1-3 seconds | Instant combustion |
| Starting capacitor | Increasing torque | Only when start | Swelling or explosion |
| Thermal relay | Overheat protection | Constantly in the circuit | No protection |
The use of a capacitor allows you to start even those engines that have difficulty starting due to thickened oil or wear of the mechanical part. However, it is worth remembering that this is only an auxiliary measure for diagnosis or resuscitation. For continuous operation without a standard relay, it is not recommended to use a capacitor circuit without installing additional protection.
Diagnostics of faults at startup
If, when voltage is applied, the compressor is silent, but there is current consumption (as can be seen from heating the wires or ammeter readings), this may indicate a wedge in the mechanical part. An attempt to start with a “kick” (a blow to the housing or a sharp start) in modern hermetic compressors rarely gives results and can finish off the unit. If the motor hums and the thermal relay immediately clicks, most likely the problem is an interturn short circuit or jamming of the piston group.
The opposite situation also happens: the engine starts, runs, but gets very hot or consumes a current higher than the rated one. This may indicate problems with the cooling system of the compressor itself (the refrigerator condenser is clogged) or that the starting winding remains in the circuit. Checking current consumption with an ammeter is the most accurate diagnostic method. The current should not exceed the values indicated on the motor nameplate.
- 📉 Low voltage in the network may be the reason why the compressor does not start even with good windings.
- 🔨 Mechanical knocking during operation may indicate destruction of the connecting rod-piston group or valves.
- 🌡️ Excessive heating of the case (more than 80-90 degrees) indicates an overload or lack of refrigerant.
It is important to distinguish between operating noise and malfunction noise. A steady hum and vibration is normal. Metallic clanging, whistling, or sharp impacts are signs of internal failure. In such cases, starting without a relay does not make sense, since the motor requires replacement or major repairs, which is impossible under domestic conditions.
Safety measures and precautions
Working with refrigeration equipment involves not only the risk of electric shock, but also the danger of high pressure in the system. Although when starting without a relay we do not directly affect the freon circuit, damage to the sealed tubes due to careless handling of the tool can lead to depressurization. In addition, some refrigerants mixed with air can form explosive compounds, although this is rare in household refrigerators.
It is strictly forbidden to leave such a temporary connection circuit unattended. The absence of a standard thermal relay or a properly configured starting device deprives the engine of protection. If the rotor jams or there is a power surge, the compressor will burn out, possibly releasing smoke and a burning smell from the windings. Always have a fire extinguisher on hand and make sure that the wiring in the room can withstand starting currents.
⚠️ Attention: Never start work on the compressor in a closed, unventilated room without access to fresh air. If the system depressurizes (for example, when a tube is bitten off) and there is a gas leak, this can lead to suffocation or poisoning from freon combustion products.
If you do not have sufficient skills in working with electrical equipment, it is better to abandon the idea of starting it yourself. An error in connecting phase and zero or mixed up windings can lead to instant failure of the compressor. In modern inverter refrigerators, such manipulations are generally impossible, since they use three-phase motors and complex electronic control boards.
Why can’t you use a conventional relay as a replacement for a standard one?
A conventional electromagnetic relay does not have thermal protection and does not take into account the position of the piston at the moment of switching on. A standard relay often has a current-dependent cut-off mechanism and bimetallic thermal protection, which are absent in a conventional relay.
FAQ: Frequently Asked Questions
Is it possible to leave the refrigerator running without a start relay all the time?
No, this is impossible and dangerous. Without a relay, the starting winding will either not turn on (the motor will not start) or will burn out if turned on for a long time. The relay is necessary to automatically turn off the starting circuit after start. Constant operation without standard protection will lead to a fire.
Which capacitor is best to use to start an old compressor?
For starting, special starting capacitors (Start Capacitor) marked CD or similar, designed for a voltage of at least 300V AC, are best suited. The capacitance is selected experimentally, starting from 2-3 µF. The use of DC capacitors is unacceptable.
Why does the compressor hum but does not start even when connected directly?
There may be several reasons: a mechanical part (piston, shaft) is jammed, an interturn short circuit in the windings, or a critically low voltage in the network. It is also possible that the internal thermal protection has tripped and has not yet cooled down. In the case of a mechanical wedge, starting without a relay will no longer help.
Is it dangerous to touch the body of a running compressor with such a scheme?
Yes, it is dangerous. With a temporary connection scheme, the standard grounding is often broken, and the insulation of the wires may be temporary. In addition, if there is a breakdown of the winding on the housing (which often happens in old motors), touching it can result in an electric shock. Always check the absence of potential on the housing with an indicator screwdriver.
Is it possible to start an inverter compressor without a control board?
No. Inverter compressors operate from a three-phase current of variable frequency, which is generated by an electronic board. It is impossible to start such a motor directly from a 220V network - it will simply burn out or not move. They require a special tester or a native control board.