The situation when the refrigerator stops freezing, and the compressor is silent or hums, but does not start, often confronts the home mechanic with a choice: change the expensive starting relay or try to start the unit directly. Direct connection motor is a temporary solution or a diagnostic procedure that allows you to understand whether the compressor itself is alive, or whether the problem lies in the protection and starting system. Understanding the principles of operation of the electric motor is critical for safe work.
In this article we will look in detail at how to bypass the starting relay, what tools are required and why you cannot leave such a circuit in operation on a permanent basis. Asynchronous motorinstalled in household refrigerators requires the creation of a rotating torque, which in normal mode provides exactly relay Bypassing this node requires precise knowledge of the winding circuit.
Before handling the wires, you need to be aware of the risks. Working with high voltage 220 volts is dangerous to life, and incorrect switching can lead to a short circuit or fire of the insulation. Safety should be priority number one, so all manipulations are carried out only when the device is disconnected from the network.
⚠️ Attention: Operation A refrigerator with a directly connected compressor without a protective relay is permanently prohibited. Such a circuit does not provide protection against overheating and overcurrent, which can lead to failure of the motor windings and a fire.
Principle of operation and design of the trigger mechanism
To correctly connect, you need to understand what we are bypassing. In the classic circuit of a single-phase refrigerator motor, there are two windings: the main (working) and auxiliary (starting) windings. Working winding has a larger wire cross-section and lower resistance, it ensures rotation of the rotor after starting. The starting winding is turned on only for a short moment of start, creating the necessary magnetic phase shift.
The standard starting relay operates on the principle of thermal expansion or electromagnetic retraction. At the moment of switching on, the current in the circuit increases sharply, the relay closes the contacts of the starting winding, the motor spins up, the current drops, and the relay opens the circuit of the starting winding. If you want to connect a compressor without a relay, you will have to manually or using a button simulate this process.
There are two main types of relays that we exclude from the circuit: posistor and induction. Posistor relay uses the property of a ceramic element to heat up and lose conductivity, breaking the circuit. The induction relay opens the contacts when the current drops after the rotor spins. Understanding this mechanism helps you realize that you cannot simply apply voltage to all contacts - the engine will hum and overheat.
- 🔌 Working winding - consumes current constantly during compressor operation.
- 🚀 Starting winding - is needed only to create torque in the first seconds.
- 🛡️ Protective function —the relay is also often combined with a thermal release that saves the motor.
It is important to note that the body of most modern compressors is already built in thermal protection (tablet), which opens the circuit during critical overheating. However, you should not rely only on it for experimental connections, since its inertia may be insufficient during sudden current surges.
Necessary tools and precautions
To carry out the work, you will need a minimum set of electricians. The main tool will be a multimeter (tester), without which it is impossible to determine the type of windings and check the integrity of the circuit. You will also need pliers, screwdrivers for removing the casing, insulating tape and, preferably, a non-latching button to temporarily close the starting circuit.
Safety is not just words. Before starting any operation, make sure that the power cord is unplugged from the outlet. Even if you plan to check operation under voltage, the initial switching of wires is carried out exclusively on a de-energized unit. Capacitor, if it is in the circuit, can retain a charge, so it should also be discharged before touching the contacts.
☑️ Checking readiness for operation
Use only serviceable wires with intact insulation. If you use homemade jumpers, make sure that their cross-section matches the current consumption of the compressor (usually at least 1 mm² for copper). Poor contact at the twisting point will lead to heating and melting of the insulation.
⚠️ Attention: Never touch exposed wires and compressor terminals while the engine is running. A voltage of 220 volts is deadly, and the metal housing of the compressor may be exposed to network potential if the insulation breaks down.
Identification of contacts and continuity of windings
The most critical stage is determining which contact is responsible for what. The compressor block usually has three terminals arranged in a triangle. They may be signed, but often the markings are worn off or missing. Here, multimeterswitched to the resistance measurement mode (Ohms) will help us.
The dialing process is simple: we measure the resistance between each pair of contacts. We need to find three values: between the working and starting windings (total), between the working and general, between the starting and general. Pairs of contacts that give the least resistance will indicate the working winding, and a pair with higher resistance will indicate the starting winding.
Table of winding resistances
Usually the resistance of the working winding is 10-30 Ohms, and the starting winding is 30-60 Ohms. The total resistance between the extreme contacts will be equal to the sum of the resistances of each winding relative to the common wire.
The common wire (Common) is always located between the working and starting contacts. If you measure the resistance between two contacts and get the maximum value, then the third, free contact is the common one. This is golden rule compressor diagnostics.
| Pair of contacts | Winding type | Expected resistance | Purpose |
|---|---|---|---|
| General - Working | Working (Run) | Low (10-30 Ohm) | Main power |
| General - Start | Start | Average (30-60 Ohm) | Engine start |
| Working - Start | Total | High (sum) | Circuit diagnostics |
| Any - Housing | Breakdown | Infinity | Insulation check |
If the multimeter shows a resistance close to zero, there is a short circuit. If the device shows one (infinity), the circuit is open. In both cases, starting the compressor is useless and dangerous. Also be sure to check the resistance between any contact and the copper tube or motor housing - there must be absolute insulation.
Direct connection diagram: step-by-step instructions
Once the contacts have been determined, you can begin assembling the temporary circuit. To do this, we need to apply phase and zero to the common and working contacts, and briefly close the starting contact with the working contact (or common, depending on the design, but more often with the working contact via a button). Let's consider the classic circuit for most household refrigerators.
Prepare two wires to connect to a 220V network. One wire (for example, blue) goes directly to the "Common" (C) pin. The second wire (brown, phase) will go to the “Working” contact (R). Now the most important point: to start, we need to apply an impulse to the “Start” contact (S).
To start, use the non-latching button. Connect one end of the button to the phase wire (which goes to the working contact), and the other end of the button to the start contact of the compressor. When you press the button, the phase will go simultaneously to both the working and starting windings, the motor will begin to rotate.
CONNECTION DIAGRAM:
220V network (Phase) -----> [Button] -----> Start contact (S)
|
+-----------------> Working contact (R)
Network 220V (Zero) -----> General contact (C)
The algorithm of actions is as follows: plug the plug into the socket (the engine is standing), press the start button (you can hear a hum and start), wait 1-3 seconds until the engine will gain momentum, and release the button. The motor should continue to run. If, after releasing the button, the motor stops and hums, it means that the holding time was too short or the starting winding is faulty.
Diagnostics of faults during startup
If, when you try to connect directly, the compressor hums, but the shaft does not spin, the problem may lie in a jammed mechanical part or a faulty winding. Jagging often occurs due to oil production or dirt entering the system. In such cases, sometimes short-term supply of voltage to the starting winding in the reverse order helps, but this is a risky procedure.
Another reason is an interturn short circuit. If the engine gets very hot, smells of burnt insulation, or knocks out the circuit breaker in the panel, it means there is a short circuit inside the windings. It is impossible to operate such a unit; rewinding or replacement of the compressor is required. Thermal relay in the standard circuit this would be what would protect the motor in such situations.
- 🔊 Humming without starting —a wedge of the piston group or a lack of phase on the starting winding is possible.
- 🔥 Heating of the case —a sign of an interturn short circuit or operation without load (rarely).
- ⚡ Knocking out plugs —breakdown of the insulation on the case or a short circuit in the circuit.
⚠️ Attention: If the compressor makes a metallic knock or grinding noise when starting directly, stop experimenting immediately. This indicates destruction of the internal suspension or valve group. Further starting will lead to complete destruction of the mechanism.
Is it possible to use a capacitor instead of a relay?
The question often arises: is it possible to connect a capacitor so as not to hold the button? Yes, for motors with a phase-shifting capacitor (which is rare for classic refrigerators, but found in some models) this is possible. However, most household refrigerators use motors with a starting winding designed for short-term operation.
If you leave the starting winding connected constantly through a capacitor, it will burn out, since the wire there is thinner and the operating mode is different. There are circuits with two capacitors (starting and running) and a switch, but their assembly requires accurate calculation of the capacitance. For diagnostics it's easier and safer to use a button.
The use of a capacitor is justified only if you are converting the motor to a different connection circuit (for example, to a three-phase network or changing the type of motor), but for a standard refrigeration compressor, the “button-start” circuit is the only correct one for tests.
Results and safety recommendations
Connecting the compressor without a relay is an effective diagnostic method that allows you to determine the state of the “heart” of the refrigerator in a couple of minutes. If the engine starts and runs smoothly, then the problem was in the relay or thermostat. If not, you will have to look for a new compressor or engage in complex repairs.
Remember that you cannot leave such a scheme “forever”. The standard relay provides not only starting, but also overload protection. Without it, the engine life is reduced significantly, and the risk of fire increases exponentially. Restoring the standard circuit is the only correct decision after diagnostics.
If you are not confident in your abilities or do not have experience working with live electrical appliances, it is better to contact a professional technician. Repairing refrigeration equipment requires not only electrical knowledge, but also an understanding of the refrigeration cycle.
Frequently asked questions (FAQ)
Is it possible to leave the compressor permanently connected via a button?
No, this is strictly prohibited. The button does not automatically turn off the starting winding, which will lead to its burnout. In addition, the lack of thermal protection can cause a fire if the motor is jammed.
Why does the compressor hum but does not start even when connected directly?
Most likely, the piston group is jammed due to lack of oil or mechanical wear. A break in the starting winding is also possible. In rare cases, a gentle blow to the body of a running compressor helps (the “impact treatment” method), but this is a temporary measure.
Which wire on the compressor is common?
The common wire is visually located between the working and starting contacts on the block. Electrically, it shows the least resistance with the working contact and average resistance with the starting contact. The sum of these resistances will give the resistance between the operating and starting ones.
Is it dangerous to touch the body of a running compressor with such a circuit?
Yes, it is dangerous. If the insulation of the windings is damaged, phase voltage may appear on the housing. Additionally, the chassis can be grounded through other structural components, which will create a path for current through your body. Always work with dielectric gloves or with protective measures.
Is it possible to use a car relay for starting?
Theoretically, it is possible to assemble a shutdown delay circuit on a car relay, but this is difficult and requires additional 12V power. It’s easier and cheaper to buy a standard start relay for your refrigerator model, which is inexpensive and guarantees proper operation.