How to Check a Refrigerator Motor Yourself and Determine Its Malfunction

Compressors are often called the "heart" of a refrigerator because they are responsible for circulating the refrigerant and maintaining the necessary temperature in the compartments. If the household appliance suddenly stops working—the motor won't start, makes strange clicking sounds, hums continuously, or shuts down a couple of seconds after starting—there is a high probability that this unit is faulty.

Calling a technician from a service center is often expensive, but you can perform a preliminary diagnosis of the refrigerator motor yourself. You won't need professional test benches for this: you just need a basic multimeter and a clear algorithm.

In this practical guide, we will thoroughly examine how to check a refrigerator compressor independently, correctly test its windings, detect a short circuit to the casing, and safely test the overload relay. This will help you accurately determine the cause of the failure and understand whether the motor can be repaired or requires complete replacement.

Preparation for Diagnosis and Safety Precautions

Before proceeding to the direct testing of the compressor, it is crucial to properly organize the workspace and prepare everything necessary. Diagnosing the electrical components of household appliances is a process that requires extreme concentration and strict adherence to safety rules. Any mistake at this stage can lead not only to the complete failure of the refrigerator but also to serious injury.

Proper preparation includes two key aspects: selecting accurate measuring instruments and ensuring personal safety when coming into contact with live parts. Let's look at what a home technician will need for the job and what rules will help conduct the check without health risks.

Necessary Tools for Testing

To perform a high-quality and safe diagnosis of the motor-compressor yourself, you will need a basic set of tools that most home technicians have:

• Digital Multimeter (Tester). This is the main instrument for the job. It will be needed to measure winding resistance (ohmmeter mode) and check for insulation breakdown to the casing (continuity mode).
• Screwdriver Set. Usually, medium-sized flathead and Phillips screwdrivers are required to remove the overload relay protective cover and dismantle mounting elements.
• Clamp Meter. Necessary for measuring the current consumption during startup and while the compressor is running.
• Pliers or Needle-nose Pliers. Useful for carefully disconnecting tightly fitted terminals from the compressor contacts.
• Fine-grit Sandpaper. Needed to clean the motor leads of oxides and soot, which guarantees the accuracy of the multimeter readings.

By preparing this simple inventory, you can move on to studying electrical safety rules that will protect you from injury when working with live circuits.

Electrical Safety Precautions

Diagnosing the electrical components of a refrigerator carries the risk of electric shock. To protect yourself during the check, strictly follow these rules:

• Complete Power Disconnection. Before starting any work, removing the overload relay cover, or testing the windings, be sure to unplug the refrigerator from the outlet. Do not rely only on the power switch on the control panel.
• Dry Conditions. Work only with dry hands. Ensure there is no moisture on the floor near the refrigerator. It is recommended to use a rubber insulating mat.
• Capacitor Discharge. If a run or start capacitor is installed in the compressor circuit, discharge it using a resistor or a special tool before touching its terminals to avoid a strong shock from the stored charge.
• Care When Applying Power. If the diagnosis requires measuring the operating voltage or running the motor directly, perform all connections with the power disconnected, and only then plug the appliance into the outlet. Never touch exposed live contacts.

Testing Compressor Windings with a Multimeter

After you have prepared the tools and de-energized the appliance, the most critical stage begins—the electrical diagnosis of the refrigerator's "heart." Testing the compressor windings with a multimeter allows you to quickly and accurately assess the condition of the electric motor without disassembling it or risking a direct startup.

This method is based on measuring the internal resistance of the copper coils hidden inside the sealed casing. Any deviation from the norm—whether an open circuit or an inter-turn short—will immediately show up on the tester's screen. Let's break down step-by-step how to correctly connect the instrument probes to the compressor leads and interpret the resulting values.

Identifying Contacts: Start, Run, and Common Terminals

On the side of the compressor, under the protective cover, there are three contacts arranged in a triangle. To check the motor correctly, you must accurately determine where the common (C), run (R), and start (S) windings are located.

To do this, set the multimeter to resistance measurement mode (ohmmeter) up to 200 Ohms and perform three simple steps:

1. Measure the resistance between all pairs of contacts (you will get three readings) and record the results.
2. Find the pair with the maximum value. The remaining third contact, which was not involved in this measurement, is guaranteed to be the common (C).
3. Determine the run and start terminals. Measure the resistance from the found common contact (C) to the two remaining leads:
   • The contact with the lower resistance is the run winding (R). It is designed for continuous operation under load.
   • The contact with the higher resistance is the start winding (S). It is connected only briefly during startup.

For a self-check, use the formula: the sum of the resistances of the run and start windings should equal (or be very close to) the value between the R and S terminals.

Measuring Winding Resistance and Detecting Open Circuits

To check the windings for an open circuit, set the multimeter to resistance measurement mode (set the range to 200 Ohms). Apply the probes alternately to the three pairs of contacts and record the readings.

When the motor is in good condition, the following rules must be observed:

• Run Winding (C–R): has the lowest resistance (usually within 10–20 Ohms).
• Start Winding (C–S): has higher resistance (approximately 15–35 Ohms).
• Total Resistance (R–S): must equal the sum of the first two measurements ($R_{C–R} + R_{C–S} = R_{R–S}$).

Compressor Family / Model	Run Winding, Ohms	Start Winding, Ohms
Atlant (SK series)	~15–20	~25–35
Danfoss (domestic series)	~10–15	~15–25
ACC / Secop	~11–14	~13–18

How to Detect an Open Circuit:
If the multimeter shows the symbol "1," "OL" (open loop), or infinity when measuring any pair of contacts, this unequivocally indicates a winding open circuit. In this case, the compressor motor will not start and must be replaced.

Checking for Breakdown and Short to Ground

Even if the resistance measurements between the terminals fall within the normal range, this does not guarantee the complete functionality of the motor-compressor. Insulation failure of the windings poses a serious danger to both the appliance and the user's safety. In such cases, electric current begins to "break down" onto the metal casing of the compressor, or the turns within one winding short-circuit each other, bypassing the useful resistance.

Such defects often lead to the immediate tripping of circuit breakers in the panel, severe motor overheating, or the appearance of dangerous potential on the refrigerator casing. To rule out these hidden threats, two crucial tests must be performed: checking for current leakage to ground and identifying possible signs of inter-turn short circuits.

How to Check for Current Leakage to Ground with a Multimeter

Checking the compressor for breakdown (winding short to ground) is a vital diagnostic step that determines the safety of using the device. If the insulation is compromised, current flows to the metal casing, which can lead to electric shock when touching the refrigerator body.

To perform the check, follow these steps:

1. Disconnect the refrigerator's power and remove the overload relay from the compressor terminals.
2. Set the multimeter to resistance measurement (megaohms) or the audible continuity test mode.
3. Clean a small area on the compressor's copper pipe or its casing of paint and rust to ensure a reliable electrical contact.
4. Press one multimeter probe against the cleaned area on the casing.
5. With the second probe, alternately touch each of the three main compressor contacts.

If the device shows infinity (symbol "1" or "OL"), the insulation is fine. Any numerical resistance value or the buzzer sound indicates a current leak. Such a compressor is faulty and requires mandatory replacement.

Signs of Inter-Turn Winding Short Circuit

An inter-turn winding short circuit is one of the most insidious failures of a refrigerator compressor. With this fault, the insulation of adjacent turns of the copper wire inside the winding is destroyed, causing part of the turns to be excluded from the circuit. As a result, the total resistance of the winding drops, and the current passing through it sharply increases.

Main signs of an inter-turn short circuit:

• Quick shutdown: The compressor starts, runs for a few seconds (or just hums), overheats significantly, after which the overload relay clicks, and the motor shuts off.
• Severe casing heating: Even over a short period, the compressor casing becomes hot to the touch.
• Reduced resistance: When testing with a multimeter, the resistance of the running or starting winding is noticeably lower than the manufacturer's specifications (e.g., showing 5–8 Ohms instead of the required 15 Ohms).

If the total resistance of the running and starting windings does not match the measured value between the start and run terminals (accounting for tolerance), or if the values are critically low—this is a clear sign of an inter-turn short circuit. Such a compressor must be replaced.

Diagnosing the Overload Relay and Direct Start

If the winding tests with the multimeter do not reveal any open circuits or shorts to ground, but the compressor still refuses to start, makes characteristic clicking sounds, or shuts down instantly, the problem often lies in the external control components. The overload relay is the key component here. It is responsible for supplying a brief pulse to the starting winding to start the motor and protects the system from overload.

Before writing off the compressor, it is necessary to locate the fault. To do this, we first check the functionality of the relay itself, and then, if necessary, perform a test start of the motor directly, bypassing the protective circuitry. This will allow us to determine with one hundred percent accuracy whether the motor-compressor itself is functional.

Checking the Overload Relay's Integrity

The overload relay is responsible for supplying a brief pulse to the starting winding and protecting the motor from overload. If the compressor hums and immediately shuts off with a click, or shows no signs of life, the problem often lies in this unit.

To diagnose, perform the following actions:

1. Visual inspection and auditory test. Carefully remove the relay from the compressor terminals and shake it near your ear. If a distinct rattling or rustling sound is heard inside, it indicates the destruction of the ceramic tablet (thermal overload). Such a relay must be replaced.
2. Checking the thermal overload resistance. Switch the multimeter to resistance measurement (ohmmeter). Apply the probes to the contacts connected to the compressor windings. For a functional relay at room temperature, the resistance should be within the range of 10–30 Ohms. A reading of "infinity" (open circuit) indicates a fault.
3. Checking the coil (for electromagnetic relays). Test the solenoid coil contacts for continuity. When flipping the relay upside down, the movable contacts inside must freely engage and disengage under the influence of gravity.

Instructions for Safe Direct Compressor Start

Starting the compressor directly (without the overload relay) is an extreme diagnostic measure that requires extreme caution. This method allows for the final exclusion or confirmation of a fault in the motor itself.

For a safe test, you will need a special diagnostic cable with a plug, equipped with three insulated terminals and a non-latching button for momentarily closing the starting circuit.

Step-by-step direct start algorithm:

1. Connection: Connect one wire of the power cable to the common terminal (C), and the second to the running winding (R).
2. Start Preparation: Connect the starting wire through the button to the starting winding (S). If there is no button, use a temporary jumper between contacts R and S, which can be quickly and safely removed.
3. Power On: Plug the cable into the mains.
4. Start: At the moment power is applied, momentarily (for 1–2 seconds) close the contacts of the running (R) and starting (S) windings. As soon as the compressor starts, immediately break this connection.

Important: If the motor does not start within 2–3 seconds, immediately cut power to the circuit to prevent overheating and winding damage.

Assessing Mechanical Condition and Current Draw

Electrical integrity of the windings and successful motor start are only half the battle. Often, the compressor starts but cannot perform its main function due to mechanical wear or hidden defects. To make a final diagnosis, its operation under load must be assessed.

At this stage, diagnostics move from simple electrical circuit checks to analyzing the physical parameters of the operating unit. We will assess how much energy the motor consumes while running and whether its mechanical part can generate the required pressure in the system.

Measuring Operating Current with Clamp Meters

Measuring the consumed current is one of the most reliable ways to assess the actual condition of the compressor under load. For this test, you will need clamp meters.

Step-by-Step Measurement Process:

1. Instrument Preparation: Set the clamp meter switch to AC current measurement mode with the minimum range (usually 2 A or 20 A).
2. Connection: Clamp only one of the power wires (phase or neutral) leading to the overload relay. If you clamp the entire two-wire cable, the instrument will show zero due to mutual magnetic field cancellation.
3. Start and Measure: Plug the refrigerator into the mains. Pay attention to two readings: the starting current (it may briefly spike to 3–6 A in the first second) and the running current (it should stabilize after startup).

Interpreting Results:

• Normal: For most domestic compressors (e.g., "Atlant" or medium-power Danfoss models), the running current is 0.8–1.3 A.
• Exceeding Normal (more than 1.3–1.5 A): Indicates mechanical jamming of the piston group or inter-turn short circuit. The motor is running overloaded, causing the relay's thermal protection to trip quickly.
• Low Current (less than 0.5–0.6 A): Indicates that the compressor is running without load. Most likely, there is a refrigerant leak, and the motor is pumping in vain.

Pressure Gauge Check and Jamming Diagnosis

If the electrical parameters are normal, but the compressor is not pumping or not starting, the problem lies in its mechanical part. A pressure measurement and jamming diagnosis are performed for a final verdict.

Pressure Gauge Check:

1. A pressure manifold is connected to the compressor's discharge port (via a Hansen quick-release coupling or a Schrader valve).
2. The compressor is started. A healthy motor should quickly build up pressure from 6 to 8 atmospheres (bar).
3. After powering off, the pressure should not drop sharply. If the needle drops quickly, it indicates wear or failure of the compressor valves (it is "not holding" pressure).

Jamming (Seizing) Diagnosis:

• Symptoms: When switched on, the compressor emits a loud hum, heats up significantly, but does not start, and after a few seconds, the overload relay clicks.
• Confirmation: If the winding resistance is normal, there is no short to the casing, the starting relay is functional, and the starting current exceeds the nominal value by several times (reaching 5–10 A) — the piston group is seized. In this case, the compressor is subject to replacement.

Conclusion

Self-diagnosing a refrigerator motor-compressor is a completely achievable task that allows you to save time and money. By step-by-step checking the winding resistance with a multimeter, ruling out shorts to the casing, testing the overload relay, and measuring the running current, you can accurately locate the fault and understand why the unit is not working.

Based on the results obtained during these checks, make a decision about the next steps:

• Replacing the Overload Relay. This is the simplest and most budget-friendly repair option. If the compressor starts successfully when run directly or if replacing the relay completely restores the operating cycle, an expensive motor replacement will not be necessary.
• Replacing the Compressor. If the diagnosis reveals a winding open circuit, inter-turn short circuit, short to the metal casing, or complete mechanical jamming of the piston group, the motor must be replaced. Such a repair requires specialized equipment (welding station, vacuum pump) and skills in refrigerant charging, so it is best left to a qualified technician.

Always observe safety precautions: perform any manipulation of electrical contacts only when the appliance is completely de-energized. If the measurement results cause doubt, consult professionals to avoid the complete failure of the equipment.