In a situation where the refrigerator suddenly stops freezing, and diagnostics indicate a faulty start-up relay, the owner of the unit faces a difficult dilemma. It often happens that replacing a part right now is impossible due to the lack of a suitable spare part or the inability to call a technician on weekends. In such emergency cases, it may be necessary to temporarily start the compressor bypassing the failed switching unit to save the products.
However, it is important to immediately emphasize that direct connection of windings is exclusively a diagnostic or emergency measure, and not a normal mode of operation. Long-term operation of the motor without automatic protection and correct phasing of currents will lead to rapid overheating and final failure of the expensive unit. Understanding the principles of operation of the electric motor will help you carry out competent diagnostics and safely perform a temporary start.
The main purpose of this procedure is to check the performance of the compressor itself and determine whether the problem lies solely in the relay or whether the fault is deeper. If the engine starts and begins to create pressure, it means that the mechanical part and electrical windings are working properly, and repairs will come down to buying a new “tablet” or starting device. Next, we will analyze in detail the design of the motor and the algorithm of actions.
The principle of operation of a single-phase asynchronous motor
In order to safely interfere with the electrical circuit, it is necessary to clearly understand exactly how it works single-phase asynchronous motorinstalled in most household refrigerators. Such a motor cannot start on its own, since the magnetic field of one winding does not create the torque necessary to move the rotor from place. To create this initial pulse, the second, starting winding is used.
In normal operation, current is supplied simultaneously to the working and starting windings, but the starting winding is turned on only for a short period of time. It is for the temporary connection of this second circuit that the starting relay is responsible. As soon as the rotor reaches about 75% of the rated rotation speed, the centrifugal mechanism or a change in current opens the starting winding circuit, and the engine continues to operate only on the working winding.
If you try to apply voltage to both windings at once and keep them on for too long, the starting winding, which has a thinner wire and high resistance, will burn out in a matter of seconds. Therefore, when starting manually, it is critically important to imitate the operation of the relay: send an impulse to the start and turn it off in time. Induction starting technology requires accuracy, since an error in the duration of switching on the starting winding is fatal to the engine.
There are two main types of starting devices, which we exclude from the circuit: electromagnetic and posistor (thermal). In the first case, the opening occurs under the influence of current, in the second - due to heating of the ceramic element. When starting manually, we need to physically close the contacts corresponding to the starting winding for 1-3 seconds until the motor reaches operating mode.
⚠️ Attention: The starting winding is designed for short-term operation. Keeping the circuit closed for more than 3-4 seconds is strictly prohibited - this will lead to burnout of the winding and expensive repair of the compressor.
Preparation of tools and safety measures
Before starting to work with electric current of 220 volts, it is necessary to ensure maximum safety. Any manipulations with the wiring must be carried out with the refrigerator completely disconnected from the network. Even briefly touching exposed live wires can lead to severe electric shock, so neglecting safety rules is unacceptable.
To carry out the startup procedure, you will need a minimum set of tools and materials. It is important to prepare everything in advance so as not to look for the right thing at the moment when the chain is already assembled. The main tool will be a screwdriver for removing the compressor casing and, possibly, pliers for fixing the wires.
- 🛠️ A set of screwdrivers with dielectric handles for safe dismantling of the housing.
- 🔌 A piece of copper wire with a cross-section of at least 1.5 mm² to create jumpers.
- 🧤 Dielectric gloves to protect hands from accidental breakdown of current.
- 🔦 Flashlight for high-quality illumination of the working area in the compressor niche.
It is also highly recommended to use a button without locking or have an assistant on hand who will quickly break the circuit. If you work alone, make sure that your circuit allows you to quickly and safely open the contacts of the starting winding. Insulation of connections - another critical point: all twists must be securely insulated with electrical tape to prevent a short circuit to the refrigerator body.
Work should be carried out in dry room, standing on a rubber mat or wooden surface. Do not allow moisture to come into contact with the electrical contacts of the compressor. If you feel unsure of your abilities or do not have basic skills in working with electrical appliances, it is better to abandon the idea of independent intervention and wait for a specialist to arrive.
Diagnostics and testing of compressor windings
Before assembling a circuit for forced starting, you need to make sure that the compressor itself is working and the problem really lies in the relay. The first step should always be a visual inspection and testing of the windings with a multimeter. This will avoid attempts to start an already burnt-out engine, which can lead to knocked out plugs or a fire.
Remove the rear protective cover of the refrigerator and get to the compressor. On its body you will see three contact pins, usually arranged in a triangle. Remove the start relay and protective box to gain access to these contacts. There is often a marking on the motor body indicating which contact is responsible for what: C (Common) - common, R (Run) - working winding, S (Start) - starting winding.
Using a multimeter in resistance measurement mode, check pairs of contacts. The resistance between the common terminal and the working winding is usually 10-30 Ohms, and between the common and starting windings - 20-50 Ohms. The resistance between the working and starting windings (through the common) will be the sum of the two previous values. If the device shows infinity (open circuit) or zero (short circuit), starting such a motor is useless and dangerous.
| Pair of contacts | Normal resistance (Ohm) | Possible malfunction |
|---|---|---|
| Common - Working (C-R) | 10 – 30 Ohm | Open or short circuit of winding |
| Common - Starting (C-S) | 20 - 50 Ohm | Open or short circuit windings |
| Working - Starting (R-S) | 30 - 80 Ohm | Circuit malfunction |
| Case - Any contact | Infinity (∞) | Breakthrough to the body (dangerous!) |
Pay special attention to checking for breakdown to the body. Press one multimeter probe to the cleaned area on the compressor body (where there is no paint), and with the other touch all three contacts one by one. The device should show infinity. If the arrow deviates or the digital indicator shows any value, it means that the insulation is broken, and operating such a refrigerator is strictly prohibited.
Connection diagram and procedure
After successful diagnostics, when you are convinced of the integrity of the windings, you can move on to the most important stage - assembling a temporary circuit. To do this, we need to apply voltage to the common and working windings constantly, and to the starting winding only briefly. For convenience and safety, it is best to use a piece of wire with a plug, which will act as a temporary power cord.
Identify the contacts on the compressor. If the marking is erased, use these continuities: the pair with the lowest resistance is the working and common windings. The third contact, left “to the side”, will be the starting one. Connect one wire from the plug (phase) to the common terminal (C). Connect the second wire from the plug (zero) to the working terminal (R). Now we have a circuit that is energized, but the motor has not yet started.
To start, you will need a third jumper. One end of this wire is connected to the start terminal (S), and the other end is not connected anywhere yet. Plug the plug into the outlet. The engine will hum, but will not start. Now you need to briefly touch the free end of the jumper to any of the wires going to the working winding (or to the common terminal, depending on the design, most often shorted S to R or C). This will create the necessary shearing impulse.
☑️ Algorithm for starting the motor
As soon as the engine starts and the hum pattern changes to the smooth hum of a running compressor, the starting winding jumper must be removed immediately. If the engine does not start on the first try, repeat the procedure no earlier than 3-5 minutes later, allowing the engine to cool and equalize the pressure in the system. A prolonged hum without rotation of the rotor indicates jamming or insufficient starting torque.
⚠️ Attention: Make sure your hands are dry and the wires are securely fixed. When touching the contacts to start, use an insulated tool or dielectric gloves to avoid electric shock.
Typical errors and possible risks
The most common mistake when starting yourself is confusion in the contacts. If you mix up the working and starting windings, the engine may start in the opposite direction (which for a refrigerator piston compressor often means no compression) or the starting winding may burn out due to prolonged current flow. Always double-check the circuit before plugging it into the network.
The second risk is related to the holding time of the starting circuit. Beginners are often afraid and release the button too early, preventing the rotor from spinning, or, conversely, hold it too long. The optimal time is 1-2 seconds. If during this time the motor does not start, it means that the problem is not in the relay, but in the motor itself (jammed piston, interturn short circuit) or low voltage in the network.
It is also worth mentioning the risk of using low-quality temporary connections. Poor contact at the point where the wires are twisted leads to sparking, heating and melting of the insulation. This may cause a short circuit. All connections must be tight, or better yet, soldered, although for a one-time diagnosis a tight twist is sufficient.
What to do if the motor hums but does not spin?
If a loud hum is heard when voltage is applied, but the shaft does not rotate, the compressor may be jammed. In some cases, the method of “tapping” the housing with a hammer through a wooden spacer during an attempt to start helps, but this is a risky procedure that can completely kill the unit. Most often, this is a sign of mechanical destruction of components inside the housing.
Do not forget that operation without a standard thermal relay leaves the motor without overload protection. If a water hammer or power surge occurs in the system, the windings will burn out instantly. Therefore, this method is only suitable for making sure: “The compressor is alive, the relay is dead,” and getting to the spare parts store.
Completing the work and installing a new relay
After you have verified that the compressor is working, you need to turn it off and let the system cool completely. The pressure in the circuit should equalize, this usually takes from 15 to 30 minutes. Only then can you plan to install a new start relay. You cannot operate a refrigerator with protruding wires and a manual starting circuit.
When purchasing a new relay, pay attention to the model of your refrigerator and the markings of the old device. Relays are selected strictly according to engine power and compressor type. There are no universal solutions here: a relay from a small refrigerator will not fit a powerful two-chamber unit. Install the new part by snapping it onto the compressor contacts and securing it with a fixing bracket.
Check the installation correctly: the relay must be located strictly in the position in which it worked previously (usually indicated by the “UP” or “This side up” arrow). An inverted relay will not perform its protection and switching function. After assembly, turn on the refrigerator and listen: the start-up should be easy, with a characteristic click after a few seconds of operation.
If after installing the new relay the situation has not changed, perhaps the problem lies deeper: in the thermostat, starting capacitor (if it is in the circuit) or in the compressor itself. In this case, you cannot do without professional diagnostics and vacuuming of the system. However, a successful manual start has already given you important information - the “heart” of the refrigerator is beating.
Is it possible to start a three-phase compressor from a single-phase network?
Theoretically, this is possible using capacitors, but such a scheme is not used for household refrigerators. Compressors for domestic refrigerators are initially designed as single-phase. Three-phase motors are found in industrial refrigeration equipment, and their conversion requires complex calculations of capacitor capacity and does not guarantee stable operation.
Why does the compressor hum, but does not start without a relay?
Humming means that electric current enters the working winding and creates a magnetic field, but there is not enough torque to move pistons from place. The starting winding creates this additional impulse. If the starting circuit does not start when the starting circuit is closed, it is possible that the motor is mechanically jammed or an inter-turn short circuit has occurred.
Is it dangerous to keep the starting winding on all the time?
Yes, it is extremely dangerous. The starting winding is made of thinner wire and is not intended for long-term operation under load. When turned on constantly, it will quickly heat up, the insulation will melt, and a short circuit will occur, which will lead to the winding burning out and a possible fire.
Is a capacitor needed to start a refrigerator without a relay?
In most modern circuits with a starting relay, a capacitor is not used, it is only needed in circuits with increased starting torque or in old models. When starting manually, we simulate the operation of a relay, so an additional capacitor is usually not required, unless the specifics of your model imply its presence in the starting winding circuit.
What to do if after starting the compressor does not freeze?
If the motor runs smoothly, but there is no cold, the problem is not in the electrics, but in the refrigeration circuit. There may be a freon leak or a clogged capillary tube. It is also worth checking whether the fan rotates (in No Frost systems) and whether the door seal is intact. In this case, the engine started successfully, but a call to a technician is required to refuel or repair the system.