The situation when the refrigerator suddenly stops cooling, and diagnostics reveals a malfunction of the starting relay often leaves the owner with a choice: buy a new part or look for a temporary solution. Sometimes it is necessary to urgently start the unit in order to save food, or it is necessary to check the performance of the motor itself by disconnecting it from the control system. Understanding the principle of operation of an electric motor allows you to solve this problem, but requires strict adherence to safety precautions, since you are dealing with life-threatening voltage.
In this article we will analyze in detail the process of directly connecting asynchronous motor a refrigeration compressor, bypassing the standard automation. This knowledge will be useful not only for emergency resuscitation of equipment, but also for those who use old compressors in homemade installations, for example, for airbrushing or inflating tires. However, remember that such a scheme is temporary or test, and it is not recommended to operate the refrigerator in this mode permanently.
Before taking up tools, you must clearly understand the risks. An electric current of 220 volts does not forgive mistakes, and the freon inside the system is under pressure. Any work must be carried out in a dry room, using proper tools and, preferably, in the presence of an assistant. If you are not confident in your skills in working with electricity, it is better to stop at this stage and call a specialist.
The operating principle and design of a single-phase motor
Most household refrigerators are equipped with single-phase asynchronous motors that are not able to start on their own. Unlike three-phase analogues used in industry, the creation of an initial torque is required here. For this purpose, the motor design provides two distinct windings: main working winding and auxiliary starting winding. It is their interaction that creates the necessary magnetic field to start the rotor.
In normal mode, the operation of these windings is coordinated by the starting relay. It supplies current to the starting winding only at the moment of start, and then turns it off when the engine picks up speed. The working winding remains energized constantly, ensuring rotation of the compressor shaft during operation. Without a relay, the starting winding will either not turn on at all or will burn out due to overheating if current is applied to it for a long time.
Sometimes you can hear the opinion that modern inverter models work on a similar principle, but this is a misconception. Inverter compressors they use frequency converters and three-phase motors, the control of which is radically different and requires complex electronics. Our instructions are relevant exclusively for classic linear compressors with a start relay, which make up the lion's share of the household appliance fleet.
Diagnostics and search for winding contacts
The first step to a successful start is to identify the winding terminals on the motor terminal block. Typically, the compressor has three contacts arranged in a triangle or in a row. On the housings of some older Soviet-made models, such as Atlant or ZIL, the terminals could be marked with letters, but in modern units you often have to rely on measurements. You will need a multimeter switched to resistance measurement mode.
The search process is as follows: you need to “ring” all pairs of contacts. You will see some resistance between any two terminals. The third pin, which is not involved in this pair, will be connected to the other two. The total resistance between the two extreme contacts (if you look at the triangle) will be equal to the sum of the resistances of the remaining pairs. The greatest resistance will be shown by the circuit between the starting and working windings connected in series.
Having identified the pairs, it is important to understand which output is which. The resistance of the working winding is always less than the starting winding. Therefore, the pair of contacts with lower resistance is the working winding, and the pair with higher resistance is the starting winding. The common wire (phase) will be the one that gives the least amount of resistance when connected to the other two. Accurate knowledge of these parameters is critical for correct switching.
☑️ Checking the motor before starting
It is worth noting an important nuance: if the multimeter shows infinity or one on the screen when any pair is dialed, this indicates a winding break. In this case, the motor is faulty and requires replacement or rewinding, which is often impractical for household repairs. It is also unacceptable to have resistance between any contact and the copper tube or motor housing - this is a sign of insulation breakdown.
Necessary tools and safety measures
To implement a direct start circuit, you will need a minimum set of tools that any home craftsman can find. The main device will be a multimeter for checking circuits. You also need screwdrivers (flathead and Phillips) for dismantling the casing and removing the relay, pliers for manipulating the wires and, possibly, a knife for stripping the insulation. It would be a good idea to have electrical tape or terminal blocks on hand for temporary connection of wires.
⚠️ Attention: It is strictly forbidden to make twisted wire connections without proper insulation. When applying 220V voltage, an uninsulated contact can lead to a short circuit, sparking and fire. Use terminal blocks or high-quality electrical tape.
Particular attention should be paid to the insulation condition of the wires going from the plug to the compressor. Often old cables have scuffs or cracks. Before connecting, make sure that the current-carrying wires are hidden. If you are using a temporary circuit with a button, make sure that its body is also dielectric and does not conduct current.
You should work with only one hand, if possible, keeping the other in your pocket or behind your back. This old rule of electricians reduces the risk of current passing through the heart in the event of accidental contact between a phase and a grounded object. The floor under your feet should be dry, and your shoes should have rubber soles. There should be no metal jewelry on your hands.
Direct connection diagram via a button
The most reliable and controllable way to start a motor without a standard relay is to use a regular button with normally open contacts (for example, a doorbell button or a switch). The essence of the method is to simulate the operation of a starting relay: we manually supply current to the starting winding only at the moment of start, and then release the button.
The connection diagram looks like this: one wire from the plug (phase) is connected directly to the output of the working winding of the compressor. The second wire from the plug (zero) goes to the common terminal of the motor. The starting winding is connected in parallel with the working winding, but a button is inserted into the gap of one of its wires. Thus, the current will flow to the starting winding only when you press the button.
Algorithm of actions when starting:
- 🔌 Insert the plug into the socket (the engine is still standing, since the starting winding circuit is open).
- 🖱️ Press and hold the start winding connection button.
- ⚡ The engine should hum and start.
- ⏱️ After 1-3 seconds, when the motor picks up speed, release the button.
If everything is done correctly, the compressor will continue to work on the working winding. If after releasing the button the motor stops or hums but does not turn, the hold time was too short or the starting winding is not receiving enough current. In some cases, you need to hold the button a little longer, but no more than 5 seconds, so as not to burn the winding.
Why can’t you leave the button pressed?
You can’t leave the button pressed all the time, because the starting winding is wound with a thinner wire and is not designed for long-term operation. It will quickly heat up and burn, which will lead to expensive repairs or replacement of the compressor.
Alternative methods and use of a condenser
There is another method that allows you to start the engine, which is often used in homemade compressor installations. It involves the use of capacitor. Unlike the push-button method, here the starting winding can remain in the circuit constantly (circuits with a working capacitor) or turn off automatically (circuits with a starting capacitor and a centrifugal switch, but they are difficult to implement without special tools).
For a one-time start or check of the motor, a circuit with a capacitor connected in series with the starting winding. The capacitor capacity is selected experimentally or according to tables, based on the engine power. Typically, refrigeration compressors use capacitors with a capacity of 2 to 4 μF with an operating voltage of at least 400V. This allows you to create the phase shift necessary to rotate the rotor.
However, using a capacitor without accurate calculation can lead to the engine heating up or operating with low efficiency. For a temporary start, reviving the refrigerator with a button is a simpler and safer way. Capacitor circuits are more suitable for stationary home-made compressors, where the engine operates in a mode other than the refrigeration cycle.
| Parameter | Working winding | Starting winding | General wire |
|---|---|---|---|
| Resistance | Low (10-30 Ohm) | High (30-60 Ohm) | Sum of resistance |
| Mode work | Permanent | Short-term (start) | Permanent |
| Wire thickness | Thicker | Thinner | - |
| Purpose | Rotor rotation | Creating starting torque | Communication with the network |
Typical errors and troubleshooting
Even with the correct scheme, beginners often make mistakes that interfere with startup or disable the equipment. One of the most common problems is mixed up contacts. If you mix up the working and starting windings, the engine may hum, but not rotate, or rotate in the opposite direction (which is critical for a refrigerator compressor, since it may not pump freon). In this case, the motor will begin to heat up quickly.
Another error is insufficient time for holding the button. If you release it too early, the rotor inertia will not be enough to switch to work from one working winding, and it will stop. If you hold it too long, the starting winding will burn out. You need to find a balance: release the button as soon as you hear the smooth hum of the running motor.
It is also worth considering the condition of the compressor itself. If it is jammed due to exhaustion of mechanical parts or lack of oil, no electric start will help it. In this case, when voltage is applied, a powerful beep will be heard, the shaft will not budge, and the thermal protection will work (if it is built into the motor) or knock out the machine in the panel.
⚠️ Attention: If, when you try to start the compressor, it makes a loud knock, a metallic clanging sound, or a burning smell, immediately stop supplying power. Further attempts may lead to destruction of the valve group or fire.
FAQ: Frequently Asked Questions
Is it possible to leave the refrigerator running without a relay all the time?
Theoretically, it is possible if you implement a circuit with a button that someone will hold, or assemble a circuit with a capacitor. However, the standard relay contains thermal protection, which turns off the motor if it overheats. By working without a relay, you are deprived of this protection, which significantly reduces the service life of the compressor and increases the risk of fire if jammed.
It hums, but does not start - what is the reason?
Most likely, the problem is a mechanical jamming of the piston group or insufficient voltage in the network. It is also possible that the starting winding is faulty (turn-to-turn short circuit) or the capacitance of the capacitor, if used, is incorrectly selected. Try to carefully, without applying excessive force, turn the motor shaft (disassembly is required), but often this is a sign of the demise of the unit.
Which wire is common if there is no marking?
The common wire is always located between the working and starting windings. If you measure the resistance between three terminals (A, B, C), then the greatest resistance will be between the two extreme ones (A and C). The third wire (B) is common. Resistance A-B will be working (less), and B-C will be starting (more), or vice versa, depending on the connection of the probes, but the sum will give A-C.
Is such a start dangerous for the electrical network at home?
With a one-time short-term start to check - no. Inrush currents are high, but short-lived. However, if you plan to use the old compressor as a garage pump, make sure the wiring can handle 5-10 amps of current, and use a separate circuit breaker to protect the line.