The situation when the refrigerator stops cooling and the motor does not make the usual sounds of operation often takes you by surprise. In most cases, the reason for the silence of the unit is a faulty starting relay, which is responsible for supplying voltage to the motor windings. Knowing how to start a compressor from a refrigerator without a start relay may be needed to diagnose the unit or as a temporary measure until purchasing a new spare part. This is a critical skill for a master who wants to understand whether the motor itself is alive or whether the problem lies in the electronics.
However, you should immediately warn: working with high-voltage equipment requires maximum concentration and compliance with all measures of extreme caution. Electric current is unforgiving of mistakes, and incorrect connection of windings can lead to instant failure of an expensive unit. In this article we will analyze the technical side of the issue, consider the connection diagrams and determine when such a start is permissible and when it is strictly prohibited.
⚠️ Attention: All manipulations to connect the compressor should be carried out only with the power supply completely disconnected from the network. Supplying voltage to the contacts is possible only during a short-term performance check.
Before starting a forced start, you must clearly understand what role the standard starting device plays. The standard electric motor circuit uses two windings: starting and working. The first is necessary to create the initial torque to move the rotor from its place, after which it must be turned off. The working winding ensures continuous rotation of the shaft during operation of the unit. If you try to apply voltage to only one of them, the motor either will not start or will begin to hum and quickly overheat.
The standard relay functions as an automatic switch that supplies current to the starting winding at the moment of start and turns it off when the speed increases. When starting manually, we will have to emulate this process, but we will have to do this manually or with the help of additional devices. It is important to understand that starting winding is designed for short-term operation, and long-term supply of voltage to it will lead to melting of the insulation and inter-turn short circuit.
To successfully implement your plan, you will need a minimum set of tools and consumables. It is better not to start the process without preparation, as searching for the necessary wires in a hurry can lead to mistakes. Prepare insulated wires with clamps, a screwdriver for removing the compressor cover and, preferably, a multimeter for preliminary diagnostics.
The principle of operation of the electric motor and types of windings
To safely start the compressor, you need to understand its internal structure. An induction motor installed in a refrigerator has a stator with two windings located at an angle of 90 degrees to each other. One of them, called the main or working one, has a larger wire cross-section and lower resistance. It is this that creates the main magnetic field during operation. The second winding, the starting winding, is made of thinner wire and has a high resistance.
The difference in resistance is a key parameter that allows you to identify contacts without documentation. If you measure the resistance between the contacts with a multimeter, you will see different values. The pair of contacts with the least resistance will point to the ends of the working winding. The pair with high resistance is the working and starting windings connected in series. The third contact, which gives the average resistance value relative to the other two, is common.
At the moment of switching on, voltage is applied to the common point and the working winding. At the same time, current is briefly supplied to the starting winding through a capacitor or directly (depending on the circuit). This creates the phase shift necessary to produce torque. Once the rotor reaches about 75% of rated speed, the starting winding should be disconnected. If this is not done, the engine will consume excess current and hum.
Why does the compressor hum without starting?
If the compressor hums but does not start, this often means that the starting winding does not receive an impulse, or the mechanical unit is jammed. In the first case, the motor tries to spin only on the working winding, which is not enough to start under freon load.
There is a common misconception that you can simply connect all the contacts together. This is categorically incorrect and will result in a short circuit. It is necessary to strictly observe the connection sequence: first, a circuit is provided for the working winding, and only for a fraction of a second is the starting circuit closed. Modern models may have several conclusions, but the principle remains the same for most household units.
Diagnostics and search for winding contacts
The first step before any connection is a visual inspection and continuity testing of the windings. Remove the plastic cover from the starter to gain access to the contact group. Usually there are three terminals there, forming a triangle. On older models they may be labeled, but often the markings are missing or worn off. In this case, a multimeter comes to the rescue.
Set the device in resistance measurement mode (Ohm). Touch the probes to any two contacts and record the readings. Then change the combination. You need to find three values. The smallest value (for example, 10-20 Ohms) will show the resistance of the working winding. The largest (for example, 30-50 Ohms) is the sum of the resistances of both windings. The average value will indicate the resistance of the starting winding.
Pay attention to the condition of the terminals. If the contacts are oxidized or covered with carbon deposits, they must be cleaned. Poor contact will result in sparking and heating, which can be dangerous. Also check the resistance between any terminal and the compressor housing. If the multimeter shows at least some resistance (not infinity), then there is a breakdown in the housing, and such a motor cannot be operated.
| Pair of contacts | Expected resistance | What does this mean |
|---|---|---|
| Contact 1 and 2 | Low (10-25 Ohm) | Working winding |
| Pin 2 and 3 | Medium (20-40 Ohm) | Start winding |
| Pin 1 and 3 | High (30-60 Ohm) | Sum of windings |
It is important to consider that in some compressor models, especially inverter type or with the No Frost system, the circuit may differ. There may be more than three pins, or the winding resistance may be very low (less than 10 ohms). In such cases, it is better to find technical documentation for a specific model compressorto avoid a fatal mistake.
Methods for manually starting a compressor
There are several ways to emulate the operation of the start relay. The simplest, but least safe method is a manual start using an insulated wire. It requires dexterity and an understanding of risks. The essence of the method is to apply voltage to the working winding, and then briefly close the starting winding circuit.
To do this, one wire from the plug (or power source) is connected to the common contact, and the second to the contact of the working winding. After plugging in, the motor will hum but will not start. At this moment, you need to touch the starting winding contact with the wire and immediately withdraw your hand. The motor should start. This method is dangerous because it is easy to get an electric shock or damage the winding if it is shorted for too long.
A safer option is to use a button without locking (for example, from a bell or old equipment). The button is connected to a break in the wire going to the starting winding. You apply power to the working winding, and then briefly press the button, sending a pulse to the starting winding. As soon as the motor picks up speed, the button must be released. This allows you to control the duration of the start pulse.
⚠️ Attention: Do not hold the start button pressed for more than 1-2 seconds. If the motor does not start during this time, further holding will lead to overheating and burning of the starting winding.
Another method involves using a capacitor of suitable capacity, if you have one at hand. The capacitor is connected in series with the starting winding. When voltage is applied, it creates the necessary phase shift. However, selecting a capacitance requires calculations, and using the wrong capacitor may not produce results or damage the engine.
Connection diagram and sequence of actions
For those who decide to act carefully, it is recommended to assemble a simple circuit with a button. You will need a power plug, two wires, a push button and insulating tape. First, determine the common contact and the contact of the working winding using the method described above. Connect the wires from the plug to them. This will be the main power circuit.
Then assemble the second circuit: connect one end of the wire from the button to the contact of the starting winding, and connect the other end of the button to the contact of the working winding (or common, depending on the design; most often the starting winding is closed with the working winding at start). Thus, pressing the button will supply voltage to the starting winding in parallel with the working one.
The sequence of actions must be strict:
1. Make sure that the plug is removed from the socket.
2. Connect the main circuit (working winding).
3. Prepare a circuit with a button (start winding).
4. Insert the plug into the socket (the motor will hum).
5. Press the button for 0.5–1 second.
6. Release the button, the motor should work.
☑️ Safe starting algorithm
If, after releasing the button, the motor continues to hum and does not develop speed, then the problem is not in the relay, but in the engine itself or the mechanical part. The piston may be stuck or there is no compression. In this case, the experiments must be stopped.
Safety precautions and possible risks
Working with 220 Volt electricity always carries a risk to life. Even briefly touching exposed wires can cause serious injury. In addition, a compressor is a high-pressure device. Incorrect handling can result in system depressurization and the release of refrigerant, which in some cases can be flammable or toxic.
One of the main dangers of manual starting is overheating of the windings. The standard relay often has thermal protection, which turns off the motor if it overheats. When started manually, this protection may not work in time, or you yourself may not notice a critical increase in temperature. Smoke, the smell of burnt insulation are signals for immediate shutdown.
It is also worth remembering the risk of electric shock when touching the housing. If the compressor's insulation is damaged or there is a breakdown in the housing, touching the metal parts of the unit can be fatal. Always use dielectric gloves and tools with insulated handles.
⚠️ Attention: Do not conduct startup experiments in a room with high humidity or on a wet floor. Water is an excellent conductor and greatly increases the risk of electrical injury.
Another risk is damage to the valve group. Frequent attempts to start "jerky" or running the starting winding for too long can lead to deformation of the valves. As a result, the compressor will work, but not pump freon, and repairs will become much more expensive than replacing the relay.
When professional repairs are needed
Manual starting without a relay is a temporary measure for diagnostics or an emergency. The refrigerator cannot be operated in this mode all the time. It's inconvenient, unsafe and ineffective. A motor operating without proper phasing and protection will quickly exhaust its service life. If the diagnostics showed that the compressor itself is working, but the relay is burned out, the right solution would be to buy a new spare part.
You need to contact a specialist if the situation has not changed after replacing the relay. This may indicate more serious problems: a break in the internal wiring, an interturn short circuit, a jammed mechanics, or a freon leak. In these cases, simple methods of “dancing with a tambourine” will no longer help.
Professional help is also needed if you are not confident in your abilities or do not have the necessary tools. An error in determining the windings costs an inexpensive relay, but can cost the cost of a new compressor. It is better to overpay for diagnostics than to finish off a working unit with incorrect actions.
Modern refrigerators are equipped with complex electronics that can block the operation of the compressor if there is no signal from the sensors. In such models, manual starting may be completely impossible without flashing the control board or signal emulation.
Is it possible to start the compressor directly from the outlet without a button?
Theoretically, it is possible if you short-circuit the starting winding with a wire and immediately break the circuit. However, this is extremely dangerous and requires a reaction that a person may not have. The risk of burning the winding or getting an electric shock is 99%. The use of a button or a starting device is strictly necessary.
Why does the compressor hum, but does not start even with the button?
Most likely, the problem is not electrical, but mechanical. The piston group could have jammed due to lack of oil or foreign objects. It is also possible that turns in the windings may be broken, causing the magnetic field to be too weak to start. The third option is the absence of freon, which means there is no load, but this is less likely to cause a hum without starting.
Will the compressor burn out if you hold down the start button?
Yes, the starting winding is designed to operate for 1-3 seconds. If you hold the button down longer, the thin winding wire will quickly heat up, melt the insulation, and short circuit will occur. At best, the compressor will stop starting, at worst, it will burn out completely.
Where can you find the markings of the windings on the compressor?
The markings are usually applied to the metal case next to the terminals or on the plastic cover of the starting relay. Designations can be alphabetic (R - working, S - starting, C - general) or digital. If there is no marking, use a multimeter to measure the resistance.
Is it dangerous to breathe fumes from burnt relay insulation?
Yes, the combustion products of plastic and insulation are toxic. If smoke starts up, immediately ventilate the room and do not inhale the vapors deeply. It is best to conduct such experiments in the open air or under a hood.