Checking a refrigerator compressor without a relay: a step-by-step guide with photos and diagrams

When the refrigerator stops freezing, but the light inside is on and the fan is spinning, the first thought is: the compressor is broken. However, before taking the equipment to a service center or buying a new unit, you should check the performance of the compressor directlybypassing the starting relay. This method helps to identify two key faults: a winding break or an interturn short circuit, which are not always diagnosed through a standard connection.

In this article - step-by-step instructions with photoshow to safely apply voltage to the compressor bypassing the relay, what tools will be needed, and how to interpret the test results. We will analyze three testing methods (with a multimeter, direct connection and through a capacitor), and also tell you which refrigerator models (for example, Indesit, Atlant, Samsung with inverter compressors) require special approach. If you have never worked with electricity, it is better to entrust the diagnostics to a specialist, but for experienced users, these instructions will save time and money.

Why the compressor is checked without a relay: the physics of the process

The starting relay in the refrigerator performs two functions: closes the circuit of the starting winding for a few seconds (to create the initial torque) and breaks itwhen the rotor picks up speed. If the relay is faulty, the compressor may not start even with good windings. Connecting directly allows you to:

• 🔍 Exclude the relay from the list of “suspects” of failure.
• ⚡ Check whether the compressor shaft rotates when feeding current to the working winding.
• 📉 Identify the interturn short circuit, which is not always detected by a multimeter.

However direct connection is always a risk. Without a relay, the compressor will not receive starting current, and if the rotor is “jammed” (for example, due to worn bearings), the windings can burn out in a matter of seconds. Therefore Before the test, be sure to check:

• 🔧 The condition of the capacitor (if it is external).
• 🛠️ The resistance of the windings with a multimeter (standards for your model).
• 🔊 The presence of extraneous sounds when rotating the shaft manually (creaking, knocking).

⚠️ Attention: If the compressor previously operated with overheating (thermal protection was triggered), direct connection may lead to short circuit. In this case, first check the integrity of the winding insulation with a megohmmeter (the norm is >2 MOhm).

Tools and preparation: what you need for the test

To diagnose a compressor without a relay you will need:

Before starting work:

1. Disconnect the refrigerator from the mains and discharge the capacitor (if any) by shorting its terminals with a screwdriver with an insulated handle.
2. Remove the starting relay from the compressor (usually it is attached on the latches or one bolt).
3. Clean the compressor terminals from oxidation (use sandpaper or alcohol).

⚠️ Attention: If there are traces of oil or rust on the compressor housing, this may indicate depressurization of the system. In this case, direct connection is pointless - replacement of the compressor or repair of the circuit is required.

Compressor connection diagram without a relay: step-by-step instructions

The refrigerator compressor has three outputs (terminals):

• C (Common) — common output.
• S (Start) —starting winding.
• R (Run) —working winding.

To start the compressor directly:

1. Check the resistance between the terminals (for standards, see the table below)

2. Make sure that the compressor shaft rotates freely (turn it by hand)

3. Prepare an extension cord with a plug for 220V supply

4. Wear dielectric gloves (or use an insulated tool) -->

1. Close terminals S and R connect a short wire (this simulates the operation of a relay).
2. Connect the phase (220V) to terminal C, and zero to the connected S and R.
3. Apply voltage for a short time (1-2 seconds!). A working compressor should:
• 🔊 Start humming (uniform sound without creaks).
• 🌡️ Start heating the housing (after 10-15 seconds).
• 🔄 Continue to work after disconnecting the starting winding (if you disconnect the wire between S and R).

If the compressor does not start:

• 🔴 Humming, but not rotates → interturn short circuit or wedging shaft.
• 🔴 Silent → winding break or short circuit to the housing.
• 🔴 Sparks → insulation breakdown (replacement required).

What to do if the compressor started, but quickly turned off?

This may indicate operation of thermal protection (built-in thermal relay). Reasons:

1. Overheating of the windings due to interturn short circuit.

2. High pressure in the circuit (capillary tube clogged).

3. Malfunction of the capacitor (if it is external).

In this case, the compressor needs to be checked under load (with the circuit connected) or the windings tested with a megohmmeter.

Winding resistance standards: how to read the multimeter readings

Before direct connection be sure to check the resistance between the compressor terminals. The standards depend on the model, but on average:

Deviations from the norms:

• 🔴 Resistance = 0 → short circuit in the winding.
• 🔴 Resistance = ∞ → winding break.
• 🔴 Resistance between terminal and body < 2 MOhm → insulation breakdown.

For accurate diagnosis of interturn short circuit (when the resistance is normal, but the compressor does not start), use current clamps or special tester (for example, UT581). At home, you can check the current consumption: a working compressor consumes 1.5–2.5 Aat startup, in operating mode - 0.8–1.2 A.

Features of checking inverter compressors

Inverter compressors (installed in refrigerators Samsung, LG, Bosch with technology No Frost) cannot be checked by direct connection to 220V. They are controlled by an inverter board, which converts alternating current into direct current with pulse width modulation (PWM). data-i="177">🔥 Burnout of the power module of the board.

• 🔥 The power module of the board burns out.
• 💥 Damage to the windings due to uncontrolled current.

To diagnose inverter models:

1. Check the resistance of the windings (for standards, see the documentation for model).
2. Test the inverter board for the presence of +12V and +5V on the control pins.
3. Use an oscilloscope to check PWM signals (if you have the skills).

If the inverter the compressor does not start, in 80% of cases the fault is control boardand not the compressor itself. Its repair is cheaper than replacing the compressor (about 3-5 thousand rubles versus 15-20 thousand for a new unit).

⚠️ Attention: B refrigerators Atlant and Biryusa with inverter compressors often fail IGBT driver on the board. It can be replaced separately, but soldering equipment and experience with SMD components are required.

Common mistakes when checking a compressor and how to avoid them

Even experienced technicians make mistakes that lead to false conclusions or damage to the compressor Let's look at the top 5 mistakes:

• 🔌 Power supply without grounding → risk of electric shock Always use RCD or connect. through separate transformer.
• ⏱️ Continuous voltage supply (>3 seconds) → overheating of the windings. The compressor should start instantly, if this does not happen, look for the reason, and do not keep it under voltage.
• 📉 Ignoring capacitor testing → if it is faulty, the compressor will not receive starting current. Normal capacitor capacity: 20–40 µF (depending on the model).
• 🔧 Checking without dismantling the relay → the relay contacts may be oxidized, which distorts the results.
• 🌡️ Testing “cold” after a long period of inactivity → the oil in the compressor thickens and the shaft may not turn before checking. let the refrigerator stand for 2-3 hours at room temperature.

Another common mistake is checking the compressor without load (disconnected from the circuit. In this case, it will start, but:

• It will not create pressure, therefore thermal protection it will not work even with an interturn short circuit.
• It is impossible to evaluate the real performance (for example, piston wear groups).

When the compressor is working, but the refrigerator does not freeze: other reasons

If the compressor is successful. passed all the tests, but the refrigerator does not cool, the problem may lie in:

To diagnose a freon leak, you can use soap solution: apply it to the suspected leak points (soldered joints, pipes). If bubbles appear, the seal is broken in modern refrigerators (for example, Liebherr) leakage is common. give aluminum tubes in places of bend.

If the reason is capillary tube, you can try to clean it yourself:

1. Bite off the tube at the filter drier.
2. Connect a nitrogen cylinder and blow towards the condenser.
3. If the stream is weak, the tube is clogged, replacement is required.

⚠️ Attention: Working with freon and soldering the circuit requires a certificate and equipment. Independent repairs without experience can lead to freon poisoning or an explosion (when mixing air with gas).

FAQ: Frequently asked questions about testing compressor

Is it possible to check the compressor without removing the relay?

Technically it is possible, but this will distort the results. The relay may have oxidized contacts or a faulty capacitor, which is why the compressor will not start even with good windings.

How to distinguish an interturn short circuit from a shaft wedge?

When there is an interturn short circuit, the compressor buzzes, but does not startand the current consumption is higher than normal. When there is a shaft wedge a metallic grinding sound is heardand the shaft does not rotate manually. short circuit can only be done with a special tester (for example, UT581) or disassembling the compressor.

What to do if the winding resistance is normal, but the compressor does not starts?

In this case, check:

1. Integrity starting capacitor (if it is external).
2. Voltage at the terminals at startup (should not be less 200V).
3. Free play of the shaft (try turning it with a screwdriver through the technological hole).

If everything is in order, but the compressor does not start, a malfunction is possible piston group (wear of the rings, valves).

Is it possible to start the compressor from a 12V battery?

No. The compressor requires 220V AC. A 12V DC supply will cause the windings to burn out. For testing in field conditions. use inverter 12V→220V, but its power must be at least 1.5 kW.

How to check the compressor refrigerator Atlant two-chamber?

In two-chamber refrigerators Atlant often used one compressor for two chambers with a solenoid valve Before checking:

1. Make sure that the valve is not jammed (check its winding - resistance ~1–2 kOhm).
2. Check the compressor according to the standard scheme, but keep in mind that it may not start if the valve has blocked the line.

If the compressor is working, but one of the chambers is not freezing, the problem is in the valve or a freon leak in a specific circuit.