The situation when the refrigerator stops freezing and the compressor is silent or makes only a quiet hum is familiar to many. Often the cause is not the motor itself, but a faulty starting relay that sends a signal to start. Before buying a new spare part or calling a technician, it is useful to conduct independent diagnostics by removing the relay from the circuit. This will allow you to understand whether engine or the problem lies deeper.
Direct connection to the network without automatic protective equipment is a risky procedure that requires strict adherence to safety precautions. Connection errors may result in short circuit or electric shock. However, if you act carefully and use measuring instruments, you can accurately determine the condition of the windings and the integrity of the electrical circuit. In this article we will look at how to safely check the performance of the unit using a multimeter and a minimal set of tools.
There are several testing methods: from simple visual inspection to measuring the resistance of the windings. Each diagnostic stage provides its own piece of information about the technical condition of the node. It is important to understand that even an electrically serviceable compressor can have mechanical defects, such as jamming of the piston group. Therefore, an integrated approach will avoid unnecessary expenses on replacing serviceable parts.
Preparation for diagnostics and safety measures
Before starting any work on electrical equipment, it is necessary to completely disconnect the household appliance. Unplug the power cord from the outlet and gain access to the back of the refrigerator. If the unit is built-in, it will have to be moved away from the niche, being careful not to damage the cooling circuit or decorative panels. The work place should be dry and well lit.
You will need a basic set of tools: screwdrivers for removing the casing, pliers and, most importantly, multimeter. Without a measuring device, diagnostics will be only speculative. Also prepare insulating tape and, possibly, new contact terminals, since the old ones may oxidize or become deformed during the dismantling process.
⚠️ Attention: It is strictly forbidden to touch live parts under voltage. All manipulations with wires and contacts are carried out only when the refrigerator is disconnected from the network. Residual voltage in the capacitors may persist for several minutes.
Remove the protective plastic or metal casing at the bottom of the rear wall. Below it you will see the compressor, capacitor (if external) and starter circuit. It is the relay, mounted on the three contact pins of the motor, that we will need to temporarily dismantle. Carefully remove the clips and disconnect the wires leading to the starter.
Visual inspection and search for external defects
Before picking up a multimeter, carefully inspect the compressor itself and the communications suitable to it. Often the cause of the malfunction is visible to the naked eye. Look for signs of soot, melted insulation, or blackened contacts. If you notice black streaks around the tube fittings or on the motor housing, this may indicate an insulation breakdown or serious overheating.
Check the condition of the copper tubes coming from the housing. If they are flattened, broken, or have obvious signs of corrosion with holes, then you cannot start the engine without restoring the tightness of the system. Working in a vacuum or with a freon leak will lead to instantaneous combustion of the windings due to lack of refrigerant cooling.
- 🔍 Inspect the contacts for oxidation and carbon deposits - they need to be cleaned.
- 🔍 Check the integrity of the insulation of the supply wires - there should be no cracks.
- 🔍 Pay attention to the condition of the springs on which the motor is suspended - they should not be compressed all the way.
Pay special attention to the place where the electrical cable enters the compressor housing. The sealed sleeve must not be damaged. If oil or moisture penetrates through it, this destroys the dielectric properties of the insulation. In such cases, even serviceable windings can show current leakage to the housing.
Method of testing windings with a multimeter
The most reliable way to check electrical integrity the motor is to measure the resistance of the windings. After removing the relay, you will see three terminals (studs) arranged in a triangle. They are usually marked, but the markings may wear off. We need to find the common point, the starting and operating windings.
Switch the multimeter to resistance measurement mode (Ohm). First check to see if there is a hole in the housing. Touch any stud with one feeler gauge and touch the paint-free area on the metal compressor housing with the other. The device should show infinity (one in the most significant digit). If you see zeros or values close to them, it means that an interturn short circuit or insulation breakdown has occurred.
Next, we measure the resistance between the contacts themselves. Depending on the refrigerator model, the resistance may vary. Typically, between the common point and the working winding it is 10-30 Ohms, and the starting winding has a slightly smaller or larger value, depending on the design of the motor. It is important that the values are stable and do not “float.”
Table of typical resistance values
For different brands of refrigerators (Indesit, LG, Samsung), normal resistance values may differ. Typically, the sum of the resistances of the two smaller arms is equal to the resistance of the largest arm (between the two extreme contacts).
If the multimeter shows an open (infinity) on any of the windings, then the circuit is broken inside the motor. It is impossible to restore such a winding at home; the compressor must be replaced. If the resistance is too low (less than 1-2 Ohms), this is a sign of an interturn short circuit, which also leads to replacement of the unit.
Checking for interturn short circuit and starting current
Simple continuity does not always reveal hidden defects. An interturn short circuit can only occur under load. For deeper diagnostics, professionals use special testers, but indirect methods can also be used. One of them is to measure current consumption during direct starting, but this requires the presence of current clamps.
If you have an ammeter, you can apply a short-term voltage while measuring the current. At the moment of starting, the current increases sharply and then drops to the nominal value. If the current immediately jumps to maximum values (10-15 Amps and above) and knocks out the circuit breaker, it means that there is a short circuit in the windings.
| Type of fault | Multimeter readings | Starting behavior |
|---|---|---|
| Normal | 10-40 Ohm (depending on the winding) | Smooth hum, operation |
| Winding break | Infinity (∞) | Silence, no reaction |
| Short circuit | Close to 0 Ohm | Humming, knocks out plugs |
| Breakage to housing | Short circuit to body | Electric shock, tripping of RCD |
It is also worth paying attention to the smell. If, when attempting to start (even briefly), a strong smell of burnt insulation appears, stop testing immediately. This is a sure sign that dielectric varnish the windings are destroyed and further operation is impossible.
Direct start of the compressor bypassing the relay
If the electrical tests are successful, you can proceed to a practical start test. To do this, you need to apply 220 Volts directly to the working winding. Be extremely careful: you are working with life-threatening voltage without the automatic protection that is usually provided by a relay and thermostat.
Determine which two pins correspond to the operating winding (usually the pair with the highest resistance, if counted from the common wire, or use the circuit diagram of your refrigerator). Connect the wires from the plug directly to these pins. We do not touch the third contact (starting) yet. Plug the plug into the outlet.
If the motor is working properly, it should start running smoothly, without strong vibration and humming. However, since single-phase motors do not have a starting winding in this circuit, it may not start on its own or may hum. At this moment, you need to briefly (for 1-2 seconds) apply voltage to the starting winding through a capacitor or simply close the circuit, simulating the operation of a relay. But it’s safer to use a button or a special starting adapter.
- ⚡ Prepare insulated wires with alligator clips.
- ⚡ Make sure your hands are dry and there are no puddles or metal objects under your feet.
- ⚡ The duration of direct switching should not exceed 5-10 seconds to avoid overheating.
⚠️ Attention: When switched on directly, the compressor operates without overheating protection. Long-term operation in this mode (more than 1 minute) without a connected cooling system (condenser and evaporator) will lead to rapid overheating and failure of the valves.
If the engine starts, listen to its operation. Extraneous knocks, metal clanging or intermittent hum indicate a mechanical breakdown inside the “pot”. In this case, even if the electrics are in order, the compressor requires replacement. Also check whether it creates a vacuum at the inlet and pressure at the outlet (you can feel it with your finger, but be careful, there may be oil there).
Analysis of results and decision making
After all the tests, it is necessary to systematize the data obtained. If the compressor rings, does not have a breakdown on the housing and starts with an even sound, then the problem does not lie there. With a 90% probability, the starting relay, thermostat or electronic control unit is faulty.
In the case where a break, short circuit or breakdown to the housing is detected, repair is not economically feasible. The cost of a new compressor and the work to replace it (including evacuation and refilling with freon) often amounts to more than 70% of the price of a new refrigerator. In such situations, it is more rational to consider purchasing new equipment.
Do not forget that replacing a compressor is a complex technological process that requires a vacuum pump, a pressure gauge station and a refrigerant cylinder. You can’t simply “resolder” the motor, the system will lose its tightness and air with moisture will damage the new compressor in a matter of days.
☑️ Criteria for replacing the compressor
Frequently asked questions (FAQ)
Is it possible to start a refrigerator without a relay forever?
Theoretically, it is possible by assembling a circuit with a capacitor or using a button, but you cannot constantly operate the refrigerator in this mode. This is unsafe and will lead to overheating of the windings, since the starting winding will not turn off or turn on correctly.
Why does the compressor ring but does not start?
This may indicate a mechanical wedge of the piston group (“sticking”) or insufficient voltage in the network. It is also possible that it is the starting device that is faulty, which does not provide a short-term impulse to the starting winding.
Is it dangerous to check the compressor without special knowledge?
Yes, it is dangerous. The risk of electric shock is high. In addition, inept actions can lead to damage to pipelines and leakage of freon, which will require expensive repairs of the entire refrigeration system.
How to distinguish the starting winding from the working one?
Usually the starting winding has a higher resistance than the working one. By measuring the resistance between the contacts, you will find the pair with the highest resistance - this is the sum of the two windings. The contact giving the average value with one of the ends of this pair is common. The winding with high resistance from the common wire is the starting one.