Starting the compressor of a refrigeration unit directly, bypassing the standard automation system, is a task that home craftsmen often encounter when diagnosing faults or creating homemade devices. Start relay plays a critical role in the standard circuit, providing a short-term voltage supply to the starting winding, but in emergency cases or for tests it can be bypassed. However, this approach requires a clear understanding of the electrical processes occurring inside the electric motor and adherence to strict sufficiency measures.
In this article we will analyze in detail the physics of the process, the necessary tools and a step-by-step algorithm of actions. Induction motorinstalled in most household refrigerators, has two main windings: working and launcher It is the correct distribution of the current phase between them that allows the rotor to move and begin to rotate. Errors in the connection can lead to humming of the motor, overheating of the windings or even a short circuit, so carefully study the theoretical part before practice.
Before you begin manipulating electrical wiring, make sure that you have basic skills in working with electricity. Working with a voltage of 220 volts is always associated with a risk to life. Direct connection without a relay is only possible for a short time for diagnostics or startup; constant operation in this mode is unacceptable. Next we will look at how to safely implement this procedure.
Principle of operation and design of the electric motor refrigerator
To successfully start the motor, you need to understand how its internal mechanism works. A refrigerator compressor is a sealed unit containing an electric motor and the pump itself. The stator windings are wound with copper wire and have different resistances: the working winding is made of a thicker wire and has less resistance, and the starting winding is thin and has higher resistance.
In normal operation, the starting relay closes the starting winding circuit only at the moment of start. As soon as the rotor picks up speed, the current in the working winding drops (or the thermal sensor is triggered, depending on the relay design), and the contacts open. The motor continues to operate only on the working winding. If you apply voltage to both windings simultaneously and leave them on, the motor will burn out.
There are two main types of motors found in household appliances: with a starting winding and capacitor motors. In refrigerators, the first option is most often used, where the phase shift is created due to the difference in the resistance of the windings or using a starting capacitor. Identification of terminals - a key stage, without which further work is impossible and dangerous.
⚠️ Attention: Never leave starting winding under voltage for longer than 3-5 seconds. It is not designed for long-term operation and will instantly overheat, which will lead to an interturn short circuit and failure of the compressor.
The sealed compressor housing usually has three terminals arranged in a triangle. Their purpose must be determined experimentally or by labeling. On modern models, the conclusions can be signed with the letters: C (Common - general), R (Run - working), S (Start - starting). If the marking is erased, you will have to use a multimeter.
Necessary tools and safety measures
Preparing the workplace and having a working tool is the key to success and safety. You will need not only a diagram, but also personal protective equipment. Working with high electric current (the starting current of the compressor can reach 15-20 Amps) requires caution.
Gather the following set of equipment before starting work:
- 🔌 A multimeter or tester for measuring winding resistance and checking circuits.
- 🔧 A set of screwdrivers and pliers with insulated handles for dismantling the casing and working with contacts.
- 🔌 Wires with alligator clips for temporary connection to the compressor terminals.
- 🧤 Dielectric gloves and insulating tape to protect hands and insulate connections.
- 💡 Incandescent lamp (power 100-150 W) for use as a control load.
Pay special attention to the condition of the wire insulation. If the cable is cracked or damaged, it is strictly prohibited to use it. Also check the serviceability of the socket into which the circuit will be plugged in. It must withstand high starting currents without sparking.
Before starting any work, be sure to disconnect the refrigerator or compressor from the power supply. Even if you plan to check the resistance, the presence of voltage in the network can lead to electric shock or damage to the measuring device. Grounding The compressor housing is also an important safety aspect, especially if the unit is old and has signs of corrosion.
Diagnostics: how to determine winding terminals with a multimeter
If there are no markings on the compressor terminals or they are unreadable, you need to independently determine which pin corresponds to which winding. For this purpose, the resistance measurement method is used. Switch the multimeter to the resistance measurement mode (Ohm) to the limit of 200 Ohm or 2 kOhm.
The measurement process is as follows:
- Clean the terminal contacts from oxides and dirt to ensure reliable contact of the probes.
- Touch any two terminals with the probes and write down resistance readings.
- Repeat the procedure for all three possible pairs of leads.
As a result, you will get three resistance values. The logic here is simple: the greatest resistance will be between the working and starting windings (total). The least resistance will be between the common terminal and the working winding. The average value will indicate the “common - starting” pair.
Let's look at an example in the table to make it clearer:
| Pair of contacts | Resistance (Ohm) | Pin |
|---|---|---|
| Pin 1 and Pin 2 | 35 Ohm | Maximum (Sum) |
| Pin 1 and Pin 3 | 15 Ohm | Average (Start) |
| Pin 2 and Pin 3 | 20 Ohm | Lowest (Working) |
In this example, Pin 3 is common, since it is involved in the pair with the lowest resistance (working winding) and in pair with the average (starting winding). Pin 2 is working, and Pin 1 is starting. Resistance may vary depending on the power of the motor, but the proportions are usually the same.
Direct connection diagram: step-by-step instructions
Once the pins have been determined, you can proceed to assembling the temporary circuit. We will use a button or switch to control the starting winding, since holding the wires with your hands is deadly and ineffective.
Connection algorithm:
- 🔌 Connect the phase wire of the 220V network to one end of the working winding (via the power switch for convenience).
- 🔌 Connect the neutral wire of the network to the common terminal of the compressor.
- 🔌 Connect the starting winding in parallel to the working winding, but insert a button (toggle switch) into the gap of one of its wires.
- 🔌 Connect the second end of the starting winding to the phase one wire (the same point where the working winding is connected).
The essence of the circuit is that when the button is pressed, voltage is applied to both windings, creating a starting torque. As soon as the engine starts, the button must be released, and the motor will continue to operate only on the working winding. If you mix up the wires, the engine will hum, but will not start, or will begin to rotate in the opposite direction (which is critical for a refrigerator piston compressor and can lead to breakdown).
☑️ Check before starting
To visualize the process, you can imagine the sequence of actions like this: you turn on the main switch, the motor hums (current flows only through the working winding, but the rotor is standing). You press the button - current flows through the trigger, the rotor breaks off. You release the button - the starting winding is turned off, the motor runs smoothly.
⚠️ Attention: The direction of rotation of the refrigerator compressor shaft is strictly determined by the design. If the connection is incorrect (if the phasing is mixed up), the compressor may not pump freon or work with overload. Make sure that there is a flow of air from the outlet pipe when starting for a short time.
Starting using a capacitor
Sometimes for a softer and more reliable start, especially if the compressor is old or the network is weak, they use starting capacitor. It creates the necessary phase shift of currents, simulating a three-phase network. The capacitance of the capacitor is selected experimentally, usually in the range from 30 to 50 uF for household refrigerators, with a voltage of at least 300V (preferably 400-450V).
The connection diagram with a capacitor is similar to that described above, but the button and the capacitor are connected in series to the starting circuit windings By pressing the button, you connect a capacitor, which gives a powerful impulse to start. After startup, the button opens, removing the capacitor from the circuit. Permanently connecting a capacitor to the starting winding is not recommended for refrigerator engines designed for short-term operation of the starting circuit.
Using a capacitor allows you to reduce starting currents and reduce the load on the network. This is especially true when operating from generators or inverters. However, if the capacitor is selected incorrectly (the capacitance is too large), the current in the starting winding may exceed the permissible value, which will lead to its combustion.
Is it possible to use a working capacitor constantly?
In some circuits (capacitor starting and capacitor operation), the capacitance remains in the circuit. But for standard refrigeration compressors this is an abnormal mode. Constant operation of the starting winding with a capacitor will change the characteristics of the motor, increase the temperature and reduce the service life.
Typical errors and troubleshooting
Even with a circuit, beginners often make mistakes. The most common is poor contact where the wires are twisted. The junction heats up, oxidizes, and the contact disappears. Always use terminal strips or quality soldering for temporary circuits.
Another common problem is ignoring the thermal state of the compressor. If you have made several attempts to start, the motor housing may have become hot. The thermal relay (if it is built into the compressor or hangs separately) may prevent it from starting until the unit cools down. It is impossible to forcibly close the thermal relay - this is a recipe for fire.
If the compressor hums, but does not start even with the starting winding:
- 🛑 The piston mechanism may have jammed (the compressor has been “seized”). You can try to revive it by briefly applying increased voltage (through a transformer), but this is risky.
- 🛑 Interturn short circuit in the windings. In this case, the resistance will be significantly lower than normal, and when trying to start, the machines will knock out.
- 🛑 Malfunction of the valve group. The motor spins, but does not create pressure. This can only be cured by replacing the unit.
It is also worth remembering about the oil. The compressor contains oil, which may have entered the circuit during transportation on its side. If you have just delivered a refrigerator or compressor, let it stand upright for at least 12-24 hours before starting it for the first time.
Frequently asked questions (FAQ)
How long can the starting winding be kept on?
The starting winding is designed to operate for 1-3 seconds, up to a maximum of 5 seconds. This time is necessary to accelerate the rotor to rated speed. Prolonged exposure to voltage will lead to rapid overheating of a thin wire and melting of the varnish insulation, which will cause a short circuit.
Is it possible to leave the compressor running without a relay all the time?
Theoretically, if you assemble a circuit with a button that you hold with your hand (or automate its shutdown), then the motor will work. But the standard relay also performs a protection function. Without thermal protection, the compressor may burn out if overloaded or jammed. For constant operation of a homemade refrigerator, it is better to buy a new universal relay, it is inexpensive.
Why does the compressor hum, but does not start?
The humming means that there is current in the working winding, and a magnetic field is created, but there is not enough starting torque. Reasons: the starting winding is faulty (break), voltage is not supplied to the starting circuit, the piston is jammed or the mains voltage has dropped. It is also possible that the oil will dry out and scuff the cylinder.
What capacitor is needed to start the compressor from the refrigerator?
Usually they use electrolytic capacitors (special starting ones) with a voltage of 300V and above. The capacitance is selected in the range of 30-50 µF. It is important to use non-polar capacitors or maintain polarity if the capacitor is polar (although special non-polar starting ones are often used for starting). Using capacitors of lower voltage will lead to their explosion.
Is it dangerous to open the sealed compressor casing?
Yes, it is extremely dangerous and impractical. There is freon under pressure inside. Opening the casing (“grinder” or hacksaw) requires special skills for subsequent sealing and charging with refrigerant. For a home mechanic, repairing an internal mechanical unit is almost impossible due to the lack of cleanliness and vacuum conditions. If the motor burns out inside, replace the entire unit.