The situation when The refrigerator stops cooling, and the compressor is silent or hums, but does not start, often indicating a faulty start relay. However, there are times when it is necessary to check the performance of the motor-compressor itself, eliminating the influence of the starting equipment. This may be required for accurate diagnostics before purchasing expensive spare parts or when checking a used unit. Understanding the principle of operation single-phase asynchronous motor will help you correctly assess the condition of the equipment.
Direct connection of the compressor to a 220 volt network is a dangerous procedure that requires strict adherence to safety precautions. If you are not confident in your abilities or do not have experience working with electricity, it is better to entrust this work to professionals. However, knowledge of the theory and algorithm of actions is necessary for every owner of household appliances in order to understand the essence of the problem and not become a victim of unscrupulous repairs.
In this article we will look at how to safely carry out diagnostics, what tools will be needed and what to pay attention to first. We will also look at typical symptoms of malfunctions and how to fix them without replacing the entire unit. Remember that hermetic compressor is the heart of the refrigerator, and its serviceability is critical to preserving food.
Operating principle and role of the start relay
To understand how to check a refrigerator without a start relay, you must first understand its function. The starting relay is responsible for briefly supplying voltage to the starting winding of the engine at the moment of starting. As soon as the rotor reaches the required speed, the relay opens the circuit and the engine continues to operate only on the working winding. Without this mechanism, starting asynchronous motor is impossible, since it does not have an initial torque.
In modern refrigerators, posistor or electromagnetic relays are most often used. PTC models operate by changing the resistance when heated, and electromagnetic models by changing the current in the working winding. If the relay is faulty, the contacts may not close or, conversely, stick, which leads either to a lack of startup or to overheating and burnout of the windings. Diagnostics begins with the exclusion of this part from the circuit.
⚠️ Attention: Direct supply of voltage to the windings without relay protective mechanisms can lead to rapid overheating and failure of the compressor. Keep your finger on the start button for no more than 2-3 seconds!
When checking, it is important to consider that the motor windings have different resistance. The starting winding usually has a higher resistance than the working winding. It is this difference and the connection sequence that determines the direction and efficiency of the rotor rotation. An error in the connection can lead to a hum, but no rotation, which can lead to thermal breakdown of the insulation.
Required tools and safety measures
Before starting any work with electrical equipment, it is necessary to prepare the appropriate tools. You will need a multimeter (tester) to measure resistance and check the continuity of the circuit, insulated wires with crocodile clips, screwdrivers for removing the casing, and possibly pliers. It is also extremely important to have a working start relay or forced start button on hand for temporary switching.
Safety is priority number one. All manipulations should be carried out only with the refrigerator completely disconnected from the network. Wear rubber gloves and shoes with insulating soles. The workplace should be dry and well lit. Do not touch the metal parts of the compressor or wiring while applying voltage.
- 🔌 Multimeter: Necessary for measuring the resistance of the windings and checking for breakdown of the housing.
- 🧤 Protective equipment: Dielectric gloves and goggles to protect the eyes from possible sparks.
- 🔧 Tools: a set of screwdrivers, side cutters, insulating tape for safe connection of wires.
- 💡 Indication lamp: optional, but useful for visually checking the presence of voltage in the circuit.
If you are using a homemade launch circuit, make sure that all connections are securely isolated. Temporary contacts should not dangle or touch the refrigerator body. Any spark in the presence of refrigerant (although the likelihood of a leak in the compressor area is small) can theoretically be dangerous, but the main threat is electrical shock. Always check the integrity of the wire insulation before connecting. Cracks or abrasions can lead to a short circuit when voltage is applied. electric shock.
Visual inspection and preparation of the compressor
The first stage of diagnosis is a thorough visual inspection. Remove the rear protective panel of the refrigerator and get to the compressor. Pay attention to the condition of the motor itself: whether there are any traces of oil, rust or mechanical damage. The presence of oil stains around the tubes or on the housing may indicate a leak in the system, which makes further checking the engine pointless without refueling.
Carefully remove the plastic casing covering the start relay and heat sensor. It is usually secured with latches or screws. Inspect the relay contacts: they should be clean, without traces of carbon deposits or melting. If you see black spots or smell a burning smell, the relay has probably already failed, and the problem may be in it, and not in the engine.
| Element | Normal condition | Symptoms of malfunction | Action |
|---|---|---|---|
| Relay housing | Intact, no cracks | Fusing, blackening | Replacement of relay |
| Contact | Shiny, clean | Soot, oxidation | Cleaning or replacement |
| Wiring | Insulation intact | Cracks, breaks | Insulation restoration |
| Thermal relay | No deformation | Bloating, burning smell | Replacing the sensor |
Disconnect the relay from the compressor. Usually it is simply removed from the three pins coming out of the motor housing. Be careful not to damage the wires. You now have access to the motor contact group. Before connecting the power, be sure to wipe the contacts with a dry cloth to eliminate the influence of oxides on the test results.
Checking the integrity of the windings with a multimeter
Before applying voltage, you must ensure the integrity of the motor windings. Take your multimeter and switch it to resistance (ohms) measurement mode. On the compressor body you will see three terminals: two upper and one lower (or arranged in a triangle). Typically, the common wire (C) is located separately, and the starting (S) and working (R) wires are located nearby.
Measure the resistance between each pair of contacts. The resistance between the working and common wires should be minimal. Between starting and general - average (3-5 times more than working). The sum of these two values should equal the resistance between the start and run contacts. If the device shows infinity (open circuit) or zero (short circuit), the compressor is faulty.
How to determine the common wire without a circuit?
The greatest resistance will always be between the starting and working terminals. The remaining third contact is the common one (C).
It is also critically important to check the breakdown on the housing. Press one multimeter probe to the cleaned area on the compressor body (where there is no paint), and with the other touch each of the three contacts in turn. The device should show infinity. If the arrow deviates or numbers appear, it means that the winding is broken into the housing, and it is strictly prohibited to operate such a compressor strictly prohibited.
- 📉 Low resistance: indicates an interturn short circuit, the engine will heat up.
- ♾️ Infinity: open circuit, current does not flow, starting is impossible.
- ⚡ Breakage to the body: deadly dangerous, requires disposal of the unit.
If all measurements are normal, you can proceed to test run. Remember that the absence of a start relay requires simulating its operation. To do this, use a button or a short-term connection of wires. The main thing is not to overexpose the starting winding under voltage.
Method of direct start of the compressor
To start without a standard relay, assemble a simple circuit. You will need a wire with a plug going to the compressor contacts. Connect one end of the wire to the common terminal (C) and the other to the working terminal (R). To start, you need to briefly apply voltage to the starting winding (S). This can be done by touching the third wire to terminal S while power is applied to C and R.
Plug the plug into the outlet. The compressor will start humming, but will not start. At this moment, briefly (for 1-2 seconds!) touch the starting contact with the wire. If the engine is working properly, it should start with a characteristic sound and start running smoothly. After starting, the wire from the starting winding must be immediately removed, since it is not intended for long-term operation.
⚠️ Attention: The duration of voltage supply to the starting winding should not exceed 3 seconds. Overheating of the starting winding will cause it to burn out in a matter of moments.
☑️ Direct start algorithm
If the compressor starts, let it run 5-10 minutes. Check to see if the case is heating up (it should be warm, but not hot), and listen to the sounds of operation. The absence of vibration, knocking and a uniform hum indicate the serviceability of the mechanical part. However, such work without a standard relay and thermal protection is only permissible for diagnostics!
Analysis of results and troubleshooting
Diagnostic results may be different. If the compressor starts and runs smoothly, then the problem was in the start relay or heat sensor. In this case, it is enough to replace the faulty part with a new one that matches the model of your refrigerator. The cost of the relay is low, and replacement takes a few minutes.
If, when voltage is applied to the starting winding, the engine hums, twitches, but does not start, several options are possible. Either the mechanical part (piston group) is jammed, or an interturn short circuit has occurred in the windings, which is why there is not enough starting torque. In such cases, the “wedging” method by applying increased voltage often helps, but this is a risky procedure, accessible only to experienced craftsmen.
In the case where the compressor does not respond at all, even with a direct connection, there is most likely an open circuit inside the motor or a burnt out winding. Repairing such a unit is not economically feasible; replacement of the compressor or the entire refrigerator is required. It is also worth checking the integrity of the supply wires inside the casing; sometimes a break occurs at the exit from the housing.
Frequently asked questions (FAQ)
Is it possible to leave the refrigerator running without a start relay all the time?
No, this is impossible and dangerous. The starting relay is necessary for the initial acceleration of the rotor. Without it, the engine will only hum and overheat the windings, which will lead to a fire or final failure of the compressor. In addition, the relay provides a break in the starting winding circuit, which is not designed for constant operation.
How to distinguish a starting relay from a thermal one?
The starting relay usually has a plastic case and is attached directly to the compressor contacts. A thermal relay (thermocouple) is often placed on the compressor housing or built into the power circuit and senses heat. In modern units, they can be combined into one unit, but functionally these are different elements: one starts, the other protects from overheating.
Why does the compressor hum, but does not start?
The most common reason is a malfunction of the starting relay, which does not supply an impulse to the starting winding. This may also indicate jamming of the piston group due to lack of oil or moisture entering the system, or an interturn short circuit of the windings when the engine loses power.
Is it dangerous to check the compressor yourself?
Yes, this is associated with the risk of electric shock 220V. In addition, inept actions can lead to short circuits or damage to serviceable components. If you do not have skills in working with electrical appliances, it is better to call a specialist. Carry out all work only with the appliance disconnected from the network.