The situation when the refrigerator stops freezing due to failure start relay, often takes you by surprise. Many craftsmen and home craftsmen wonder whether it is possible to temporarily start the unit bypassing the burnt part. Theoretically, start the compressor directly possible, however, this process requires a deep understanding of electrical circuits and strict adherence to safety precautions. Ignoring the nuances can lead to final engine failure or injury.
In the standard scheme of motor operation, it is the starting device that is responsible for briefly supplying voltage to the starting winding, creating the necessary torque. Without this impulse, the rotor simply hums, but does not rotate. A temporary connection without a standard relay is often used for diagnostics or as an emergency measure to evacuate products, but it is extremely undesirable to constantly operate equipment in this mode.
Before you begin any manipulations with electricity, you must be aware of the risks. Working with 220 volt mains voltage is life-threatening. In addition, improper switching of windings can instantly burn the insulation or cause a short circuit. In this material we will analyze the technical aspects of forced starting, connection diagrams and methods for checking the integrity of the windings.
The principle of operation and the role of the starting device
Single-phase asynchronous motors, which are installed in most household refrigerators, are not capable of starting rotation on their own. To start, they need to create a phase shift, which is achieved by connecting a second, starting winding. This is exactly what starting relaydoes, which can be electromagnetic or posistor. At the moment of switching on, it closes the circuit of the starting winding, and after the rotor accelerates, it opens it.
If the relay is missing or faulty, current flows only through the working winding, creating a pulsating magnetic field that is insufficient to break the rotor from its place. The engine begins to hum strongly and heat up. To bypass this mechanism, it is necessary to artificially simulate the process of applying a pulse to the starting winding at the moment of switching on.
There are several ways to implement this task: from using a button to manually switching wires. However, it is worth remembering that modern inverter models may have a completely different motor design, where direct starting without a controller is impossible in principle. We are considering classic piston units.
- 🔌 Electromagnetic relay —closes the circuit at a certain current, typical of older models.
- 🔥 Posistor relay —uses a heating element to open the circuit, common in modern technology.
- ⚙️ Capacitor starting —requires a capacitance to create a phase shift.
⚠️ Attention: Forced starting without a relay deprives the motor of overload protection. If the rotor jams or the load is excessive, the windings will burn out in a matter of seconds. Do not leave the compressor turned on unattended for even a minute.
Necessary tools and preparation
To carry out work on connecting the compressor, you will need a minimum set of tools, which are found in most home craftsmen. It is critical to have a working multimeter to test continuity and determine winding leads. Without it, working blindly is tantamount to a lottery with a high risk of losing.
You will also need insulating material, pliers, screwdrivers and, possibly, a non-latching button for convenient control of the starting impulse. If you plan to use the capacitor starting method, you will need to select a capacitance of the appropriate value, usually 2-4 uF for medium-power motors.
Before starting any actions, be sure to turn off the power to the refrigerator. Unplug the cord from the outlet. Even if you plan to immediately apply voltage for testing, the initial installation of the circuit should be done with the device completely de-energized. This is a basic rule of electrical safety.
☑️ Preparation for startup
Visually check the condition of the windings for blackening or a burning smell. If the insulation is broken, starting such a unit is useless and dangerous. Make sure that there is freon in the system, although for a short-term start of the compressor without a load on the cooling system this is not a critical parameter, but a vacuum pump can quickly fail when running dry.
Determining the winding terminals with a multimeter
The most important step before connecting is the correct identification of the contacts. The compressor terminal block usually has three terminals. They may be signed, but often the markings are worn off or missing. In this case, a multimeter switched to resistance measurement mode (Ohm) comes to the rescue.
Ring all pairs of contacts with each other. You will get three resistance values. The sum of the two smaller resistances must be equal to the largest. The highest resistance is the sum of the resistances of the starting and working windings, that is, the measurement takes place between the extreme terminals. Between these same terminals, the resistance will be maximum.
The winding with higher resistance is the starting winding, and the one with lower resistance is the working (running) winding. The common wire (phase) is located between them. Correct definition working and starting windings guarantees that the engine will start in the right direction and will not burn out.
| Pair of contacts | Nature of resistance | Purpose outputs |
|---|---|---|
| Contacts 1-2 | Small (for example, 20 ohms) | Working winding |
| Contacts 2-3 | Medium (for example, 30 Ohm) | Start winding |
| Contacts 1-3 | Sum (50 Ohm) | Total resistance |
What to do if the resistances are the same?
In some motors, the winding resistances may be close. In this case, the starting winding can often be determined by the thickness of the wire (it is thinner) or experimentally by applying a short-term pulse.
Schemes for direct connection of a compressor
There are several proven methods for starting a motor without a standard relay. The simplest and most accessible way is to use a non-latching button (for example, from a doorbell). The circuit is assembled like this: the phase is supplied to the common wire, the zero is constantly supplied to the working winding, and the starting winding is powered through a button in parallel to the working one.
When the button is pressed, voltage is supplied to the starting winding, creating torque. As soon as the motor shaft spins up (usually within 1-2 seconds), the button must be released. If everything is done correctly, the motor will continue to operate on the working winding. This method requires some skill.
A more advanced option is to use a capacitor. It is connected in series with the starting winding and is constantly in the circuit (or only at the time of starting, if a circuit with a button is used). The capacitor creates a phase shift, improving the starting characteristics and efficiency of the motor.
Connection diagram with a button:Network (L) --> General contact
Network (N) --> Working winding
Network (L) --> Button --> Start winding
Checking functionality and starting
After assembling the circuit, you can proceed to testing. Plug the plug into the outlet. The engine should be silent. Click the start button. If you hear a confident hum and feel vibration, and the shaft begins to move, release the button. The motor should continue to hum smoothly, without sudden surges in current.
Pay attention to the direction of rotation of the shaft (if visible) or to the presence of pressure at the compressor outlet. When working properly, air pressure should be felt from the outlet tube. If the motor hums but does not spin, the windings may be reversed or there is not enough starting torque.
During operation, regularly check the temperature of the motor housing. The hand must tolerate touching metal. If the compressor heats up within 30-40 seconds, it means there is a problem with the windings or operating mode. In this case, immediately turn off the power.
⚠️ Attention: If the circuit breaker in the panel is knocked out during startup or a cracking sound is heard, stop trying immediately. This indicates a short circuit in the windings or a breakdown to the housing.
Typical errors and safety measures
One of the most common mistakes is ignoring phasing. Although a single-phase motor will often start in either direction, improper connection can result in single-winding operation or insufficient torque. Always double-check the circuit before applying voltage.
Another mistake is using wires that are too thin for connection. Compressor starting currents can be 5-7 times higher than the rated current. A thin wire can melt, creating a fire hazard. Use copper wire with a cross-section of at least 1.5 mm².
Do not forget about grounding. The compressor and refrigerator housing must be grounded. In a garage or workshop, this is often neglected, which is a serious mistake. If the insulation breaks down, there will be a dangerous potential on the case.
- 🚫 Do not touch metal parts when the power is on.
- 🚫 Do not hold the start button for longer than necessary.
- 🚫 Do not leave working the unit is unattended.
Frequently asked questions (FAQ)
Is it possible to leave the refrigerator running without a starting relay all the time?
Theoretically, if the correct circuit with a capacitor is selected, the engine can run for a long time. However, the lack of standard protection (thermal relay) makes such operation risky. If there is a power surge or the piston group jams, the engine will burn out. It is recommended to use this method only as a temporary solution.
Why does the compressor hum but does not start without a relay?
This means that the impulse is not supplied to the starting winding or it is too weak. The rotor cannot overcome inertia and magnetic sticking. It is necessary to check the integrity of the starting winding and the correct connection of the phase to this pin at the time of start.
What capacitor is needed for starting?
For most household refrigerators, starting capacitors with a voltage of at least 300-400V and a capacity of 2 to 4 μF are suitable. Using a capacitor with a smaller capacity will not provide the required torque, and a larger one may overheat the winding.
Is it dangerous to start a compressor outside the refrigerator body?
Yes, it is dangerous. First, there is a risk of electric shock from exposed contacts. Secondly, the compressor can throw out oil along with freon under pressure. Thirdly, without a radiator on the body, the engine may overheat faster than usual.