Checking the refrigerator motor without a relay: a detailed guide with diagrams

When the refrigerator stops freezing, the first suspicion falls on the compressor - the “heart” of the unit. But how can you be sure that this is the problem if you don’t have a spare relay or a multimeter with a function for checking the starting windings? Experienced craftsmen know: you can diagnose a motor without a starting relayusing available tools and basic knowledge of electrical engineering.

In this article we will examine 5 reliable methods for checking the compressor without a relay - from visual inspection to direct connection to the network in compliance with all safety measures. You will learn what signs indicate turn-to-turn short circuit or winding breakagehow to correctly “ring” the contacts and what to do if the engine hums but does not start. Important: all the described actions are suitable for most household refrigerators (Atlant, Indesit, Samsung, LG, Biryusa etc.), but require extreme caution when working with electricity.

Before you begin diagnostics, remember: the refrigerator compressor operates under high pressure and contains refrigerant. Incorrect actions can lead not only to electric shock, but also to freon leakage or mechanical damage. If you are not confident in your skills, it is better to contact a specialist.

1. Preparation for testing: what needs to be done before diagnosis

Before checking the motor, it is necessary to exclude other possible causes of the malfunction. Start with simple steps:

• 🔌 Check the power supply: make sure that the outlet works (connect another device) and the refrigerator's power cord is not damaged. Sometimes the problem lies in the oxidized contacts of the plug.
• ❄️ Evaluate the temperature in the chambers: if the refrigerator does not freeze well, but the compressor turns on, it may be a freon leak or a clogged capillary tube.
• 🔊 Listen to the sounds: a hum without starting the engine may indicate a malfunction of the starting relay (even if you turned it off), and silence - a break in the winding.
• 📏 Inspect compressor housing: cracks, traces of oil or rust on the tubes are a signal of mechanical damage.

If there are no external signs of breakdown, but the refrigerator still does not work, proceed to diagnose the motor. To do this you will need:

• 🔧 Screwdriver (Phillips/flathead) - to remove the protective casing.
• 📊 Multimeter (tester) - to check the resistance of the windings.
• 🔌 Extension cord with grounding - for a safe connection.
• 🧲 Magnet - to check the tightness of the case (optional).

⚠️ Attention! Before starting work unplug the refrigerator and discharge the capacitor (if it is in the circuit). Even when turned off, capacitors can store a dangerous charge.

2. Visual inspection of the compressor: 4 signs of malfunction

Start with an external inspection of the motor. Even without tools, you can identify obvious problems:

1. Oil smudges on the body or tubes. This is a sign of depressurization of the system or wear of the seals. In this case, the compressor must be replaced.
2. Rust on the contacts or threaded connections. Oxidation worsens electrical contact and can lead to overheating of the windings.
3. Swelling or cracks on the housing. Indicates overheating or mechanical damage (for example, from vibration).
4. Burnt wires on the terminals. This is a consequence of a short circuit or incorrect connection.

Pay special attention three tubescoming from the compressor:

• 🔹 Thin (suction) - must be cold when operation.
• 🔹 Thick (discharge) - heats up to 60–90°C.
• 🔹 Soldered (service port) - should not be damaged.

If the tubes are covered with frost or condensation, this may indicate insufficient thermal insulation or malfunction of the thermostat. In this case, check the door seals and temperature settings.

What to do if there is rust on the compressor?

Clean the contacts with fine sandpaper (600-800 grit), then treat with alcohol. If the rust is deep, replace the terminal block or compressor.

3. Checking the winding resistance with a multimeter

The most reliable diagnostic method is to measure the winding resistance. To do this:

1. Remove the compressor protective casing (usually secured with 3-4 bolts).
2. Disconnect the wires from the terminals (take a photo of the connection diagram!).
3. Find three contacts:
   • C (common) - general;
   • S (start) - starting winding;
   • R (run) - working winding.

Switch the multimeter to resistance measurement mode (200 Ohms).

Now take measurements between pairs of contacts:

If the multimeter shows 0 (short circuit) or ∞ (open) - the compressor is faulty. Also check resistance between the terminals and the housing: it should tend to infinity. Any value below 1 MOhm indicates an insulation breakdown.

⚠️ Attention! Some modern compressors (for example, in refrigerators Samsung with inverter motors) have built-in electronics. Checking them requires special equipment - without it, diagnostics can give false results.

4. Direct connection of the compressor to the network: step-by-step instructions

If the windings are working, but the motor does not start, you can check it by directly connecting to the network without a relay. This method requires caution!

You will need:

• 🔌 An extension cord with a plug and bare wires at the other end.
• 🔧 Electrical tape or terminal strips clamps.
• ⏱ Timer (you can use a smartphone).

Action algorithm:

1. Connect one extension wire to the contact C (common).
2. Second wire shortly (for 1-2 seconds!) touch the contact S (starting winding).
3. If the motor hums and starts to rotate, switch the wire from S on R (working winding).
4. The compressor should continue to run. If it stops, there is a problem in the windings or mechanical part.

Never connect the compressor to the network for more than 3-5 seconds without load (without freon in the system)! This can lead to overheating and final breakdown.

What do the results mean:

• ✅ The motor starts and runs smoothly - the relay is faulty, the compressor is working.
• ❌ The motor hums, but does not rotate - the piston is jammed or the windings are faulty.
• ⚡ The motor sparks or smokes - a short circuit, replacement is required.

5. Checking the mechanical part: how to identify jamming

If the electrical part is working, but the engine does not start, the problem may be mechanical. Frequent causes:

• 🔧 Piston jamming due to wear or metal shavings.
• 🛢 Lack of oil in the crankcase (the compressor runs dry).
• 🔄 Valve failure —the motor hums, but does not create pressure.

How to check:

1. Disconnect the compressor from the network.
2. Remove the protective cover to gain access to shaft.
3. Try to turn the shaft manually (for example, with a wrench by the pulley). If it does not rotate or requires a lot of force, the motor is jammed.

If the shaft rotates freely, but when connected to the network, the motor does not start, the problem may be:

• 🔋 Insufficient voltage (check the network with a multimeter).
• 🧲 Loss of the magnetic properties of the rotor (rare, but found in older models).
• 🔧 Wear of the bearings —a metallic grinding sound is heard.

⚠️ Attention! If the compressor is jammed, do not try to disassemble it yourself! There is freon inside under pressure, and depressurization of the system will require professional refilling.

6. Diagnostics by sounds and vibration: what different noises mean

The nature of the noise of a compressor can tell a lot about its condition. Here are the main “symptoms”:

If the motor starts but turns off after a few minutes, check:

• 🌡️ Thermostat —it may be triggering falsely.
• 🔌 Network voltage - low voltage leads to overheating.
• 🛠 Condition of the capacitor (if it is in the circuit) - its capacity could have decreased.

In refrigerators with a system No Frost additional noise may come from the fan or defrost heater. Before diagnosing the compressor, make sure that the problem is not with them.

7. When the compressor is working, but the refrigerator does not freeze

If the motor is running, but the temperature in the chambers does not drop, the problem may not be in the compressor. Check:

• 🔍 Freon leak: listen for hissing or inspect the tubes for oil stains. Oil often accumulates at the leak site.
• 🧊 Clogged capillary tube: the compressor heats up, but the condenser (grid at the back) remains cold.
• 🔄 Malfunction of the thermostat: if it does not send a signal to when turned on, the motor will not work despite its working order.
• 🌡️ Problems with sensors (in electronic models): for example, the evaporator sensor may give false readings.

To check for freon leakage, you can use a soap solution: Apply it to suspicious areas (pipe connections, soldering joints). If bubbles appear, there is a leak. In this case, you will need recharging the systemwhich is best entrusted to a specialist.

If the capillary tube is clogged, the compressor will work without stopping, but the freezer will not cool. It is almost impossible to clean it at home - you will need special equipment.

FAQ: Frequently asked questions about checking the compressor

Is it possible to check the compressor without a multimeter?

Yes, but the diagnosis will be less accurate. You can:

• Ring the windings with a light bulb (220V) with a battery - if the lamp is on, there is no break.
• Try direct connection to the network (see section 4).
• Evaluate the heating of the tubes: if the discharge tube does not heat up, the compressor does not create pressure.

However, without measuring resistance, you will not be able to identify an interturn short circuit.

What to do if the compressor hums, but does not start?

This is a typical sign:

• Piston jamming (try turning shaft manually).
• Faults in the starting winding (check the resistance C→S).
• Low voltage in the network (must be at least 200V).

If the shaft rotates freely and the windings are working properly, the problem may be in the capacitor (if it is in the circuit).

How to distinguish a compressor malfunction from a thermostat breakdown?

The easiest way:

• If the motor is does not turn on at all - check the thermostat (close its contacts directly).
• If the motor it hums, but does not start the problem is in the compressor or start relay.
• If the motor works without stops check the thermostat or sensors.

Is it possible to start the compressor without a relay on a permanent basis?

No! A starting relay is needed for:

• Closing the starting winding at the time of start.
• Overheat protection (in some models it is built-in thermal protection).
• Correct distribution of the load on the windings.

Without a relay, the compressor will overheat and quickly fail.

How much does it cost to replace a compressor at a service center?

The cost depends on:

• Refrigerator brand (for example, for Atlant cheaper than for Liebherr).
• Type of compressor (regular or inverter).
• The need to refill freon (if there was a leak).

On average replacement costs 8,000–20,000 rubles (2026), including work and a new compressor. For older models (over 10 years old), repairs are often unprofitable.