How to independently check a refrigerator compressor without a relay: a detailed guide

Introduction: why check a compressor without a relay?

The compressor is the “heart” of the refrigerator, and its malfunction leads to complete failure of the equipment. Often, owners are faced with a situation where the unit does not start, but it is not clear whether it is their own fault compressor or starting relay. Testing without a relay allows you to accurately determine whether the motor is working, excluding the influence of auxiliary elements.

The difficulty is that without a relay, the compressor will not receive the required voltage to start - it will have to be started manually or through a direct current supply. This method requires caution: incorrect actions can damage the windings or even cause short circuit when 220V is supplied directly to the working winding without protection. However, with the right approach, diagnostics will take no more than 30 minutes and will save money on calling a technician.

This article contains step-by-step instructions with photos, connection diagrams, signs of malfunctions and answers to frequently asked questions. All methods have been tested on compressors Danfoss, Embraco, Secop and other popular brands.

Preparation for testing: tools and safety measures

Before starting work, be sure to disconnect the refrigerator from the network and discharge the capacitor (if it is in the circuit). To check a compressor without a relay you will need:

• 🔧 Multimeter (to measure winding resistance and voltage).
• 🔌 Wires with terminals ("crocodiles") with a cross-section of at least 1.5 mm².
• 🔄 Start relay from another refrigerator (optional, for comparison).
• 📏 Screwdriver and pliers (for dismantling the relay).
• 🔋 220V power supply with the ability to quickly turn off (for example, an extension cord with a button).

⚠️ Attention: Never supply 220V directly to the compressor without protection! Use starting capacitor (if it is provided in the circuit of your model) or short-term launch via a button. Long-term operation without a relay will lead to overheating of the windings.

Before starting, inspect the compressor for physical damage:

• 🔍 Cracks or swelling on the housing (a sign of interturn short circuit).
• 💨 Strong carbon deposits on the contacts (indicates insulation breakdowns).
• 🛢️ Oil leaks from under the flange (may indicate wear of the piston group).

Compressor connection diagram without relay: 3 options

To start the compressor bypassing the relay, you need to apply voltage to the correct contacts. Most models (Danfoss SC10G, Embraco EG80HLE etc.) have three outputs:

1. Common (C) —middle contact.
2. Working winding (R) —usually the right one.
3. Starting winding (S) —usually left.

Below are diagrams for different types of compressors. If the markings are different on your model, check the technical data sheet.

⚠️ Attention: If the compressor is installed thermal relay (a small box on the case), it cannot be turned off - this protection against overheating. Forced starting without it can lead to fire of the windings.

How to determine the pins if there are no markings?

If the contacts are not labeled, use a multimeter in mode resistance:

1. Measure the resistance between all pairs of contacts.

2. The highest resistance is C-S (common + starting).

3. Average - C-R (common + working).

4. The lowest - R-S (working + starting).

Method 1: Checking the winding resistance with a multimeter

This is the safest diagnostic method, which does not require voltage supply. It helps to identify:

• 🔌 Winding break (resistance = ∞).
• 🔥 Interturn short circuit (resistance below normal).
• ⚡ Breakdown to housing (resistance between terminal and body ≠ ∞).

Normal resistance values for popular models:

Step-by-step instructions:

1. Disconnect the compressor from the network and remove the relay.
2. Switch the multimeter to resistance measurement mode (200 Ohm).
3. Measure the resistance between all pairs of contacts (C-R, C-S, R-S).
4. Check the resistance between each terminal and the compressor housing (should be ∞).

The power supply to the refrigerator is turned off|

The starting relay is removed|

Multimeter in 200 Ohm mode|

All 3 pairs of contacts have been checked|

The resistance to the case has been checked|-->

If the resistance between the case and any terminal is not infinite, the compressor is broken and must be replaced. If the resistance of the windings is very different from the norm. (for example C-R = 5 Ohms instead of 15), this indicates an interturn short circuit.

Method 2: Direct start of the compressor without a relay (for experienced ones)

This method allows you to make sure that the compressor is mechanically sound and capable of creating pressure. Danger: possible if connected incorrectly winding failure or electric shockUse only if you are confident in your skills!

Necessary conditions:

• 🔌 Availability starting capacitor (if it is provided in the circuit of your model).
• 🛠️ Possibility of quickly turning off the power (for example, with a button on the extension cord).
• 👓 Protective gloves and glasses (in case of a pipeline rupture).

Step-by-step instructions:

1. Connect 220V to the contacts C (common) and R (working winding).
2. Briefly (for 1-2 seconds) touch the contact with the wire S (start winding). The compressor should start.
3. If the compressor hums but does not start, the problem is starting winding or mechanical parts (jammed piston).
4. If the compressor starts but immediately turns off, check thermal relay (overheat protection may be triggered).

⚠️ Attention: Do not keep the compressor turned on for more than 10–15 seconds without a cooling system! It will quickly overheat, since there is no refrigerant circulation and no protection from the relay.

Method 3: Checking the current consumption (for accurate diagnosis)

Measuring the current allows you to identify hidden defects that are not visible when checking the resistance. For example, interturn short circuit at an early stage or bearing wearincreasing the load.

Normal current values:

• 🔌 Starting current: 8–12 A (short-term at start).
• 🔄 Operating current: 0.8–1.5 A (after starting).

How measure:

1. Connect the multimeter in current measurement mode (up to 10 A) series with the working winding (C-R).
2. Shortly apply voltage to C-S to startup.
3. Fix the starting and operating current.

If the current exceeds the norm (for example, operating current = 2.5 A), this indicates:

• 🔥 Interturn short circuit in the windings.
• 🛢️ Wear of the piston group (increased friction).
• 🔧 Seizing of the shaft or bearings.

What to do if the current is too high?

If the operating current exceeds 1.8 A, the compressor works for wear. case:

1. Check the oil level (through the sight glass, if available).

2. Listen to the compressor for extraneous noise (grinding, knocking).

3. If possible, measure the discharge pressure (should be 10–15 bar for R134a).

If the parameters are not normal, the compressor must be replaced.

Method 4: Diagnostics by sound and vibration

Even without tools, you can first assess the condition of the compressor by characteristic signs:

• 🔇 Silence when turned on - break windings or lack of power.
• 🔊 Hum without starting —fault in the starting winding or shaft jamming.
• 💥 Clicks and shutdown —thermal protection (overheating) triggered.
• 🛠️ Grinding or knocking —wear of the piston group or bearings.

How to check:

1. Plug in the refrigerator and listen to the compressor.
2. If a hum is heard, but the motor does not start, briefly apply voltage to the starting winding (as in Method 2).
3. If the compressor starts, but after a few seconds it turns off, the problem is thermal relay or overheating.

⚠️ Attention: If the compressor emits metallic grindingit cannot be used! This is a sign of destruction of internal parts, and further work will lead to depressurization of the system.

Method 5: Checking pressure (for professionals)

This method requires knowledge of pressure manifold and skills in working with refrigerants. It allows you to evaluate compressor performance and identify leaks in the system.

Step-by-step instructions:

1. Connect pressure gauges to suction and discharge nozzles.
2. Start the compressor (via a relay or manually, as in Method 2).
3. Measure the pressure:
   • 🔹 Suction: 0.5–1.5 bar (depending on the refrigerant).
   • 🔹 Discharge: 10–15 bar (for R134a), 20–25 bar (for R600a).

Compare with the compressor data sheet.

If the discharge pressure is below normal, this may mean:

• 🛢️ Wear of valves (not sealed).
• 🔧 Refrigerant leakage in the system.
• 🔥 Interturn short circuit (the compressor does not develop full power).

⚠️ Attention: Working with refrigerants requires certification! Incorrect handling of R600a (isobutane) can lead to an explosion, and R134a to poisoning. If you have no experience, entrust this check to a specialist.

Common mistakes when checking a compressor without a relay

Even experienced technicians sometimes make mistakes that lead to false conclusions or damage to equipment. Here are the most common ones:

• ⚡ 220V supply directly to the starting winding —this causes overheating and failure. Correct: a short-term impulse of no longer than 3 seconds.
• 🔌 Ignoring the thermal relay - turning it off can lead to fire of the windings.
• 📏 Incorrect identification of contacts - always check the resistance with a multimeter, even if there is a marking.
• 🛠️ Starting the compressor without oil —if the oil level is low (visible through the inspection window), long-term operation without it will destroy the piston group.
• 🔍 Diagnostics without disconnecting the refrigerator from the network —risk of electric shock during measurements.

If after checking you doubt the results, pay attention to indirect signs:

• 🔥 The compressor gets very hot even after short-term operation.
• 💨 The refrigerator does not freeze, but the motor runs without stops.
• 🛢️ Frost or condensation appears on the compressor tubes in atypical places.

FAQ: Answers to frequently asked questions

Is it possible to check an inverter compressor without a relay?

No. Inverter compressors (for example, in refrigerators LG, Samsung, Hitachi) are controlled by an electronic board. They cannot be started directly - this will lead to failure of the power module. Diagnostics is only possible through the service menu or replacing the board.

What resistance should be between the windings?

For most household ones. compressors:

• C-R: 10–25 Ohm (working winding).
• C-S: 20–40 Ohm (starting winding).
• R-S: 15–30 Ohm (total resistance).

If the values are beyond these limits, the windings are faulty.

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

Causes and solutions:

1. Faulty starting relay - replace with a known working one.
2. Shaft jamming —try to manually rotate the shaft (through the pulley, if there is access).
3. Low voltage in the network —check with a multimeter (should be 220V ±10%).
4. Breakage of the starting winding — measure the resistance C-S (should be 20-40 ohms).

How to check the compressor if you don’t have a multimeter?

Without tools you can do the following:

1. Listen to the compressor when you turn on the refrigerator:
   • Silence - winding break or no power.
   • Hum without starting - problem with the starting winding or mechanical blockage.

Touch the compressor housing after 5-10 minutes operation:

• Cold - no current (check power, relay, thermostat).
• Excessively hot - interturn short circuit or overload.

For accurate diagnostics, a multimeter is still needed.

Is it worth repairing the compressor or is it better to buy a new one?

Compressor repair is advisable only in the following cases:

• 🔧 Replacement starting relay or thermal protection (cost 500–1500 rubles).
• 🛢️ Adding oil (if there is an inspection window and the compressor is not sealed).

If a malfunction of the windings, piston group or valves is diagnosed, the compressor must be replaced. The cost of a new one. compressor (for example Danfoss NL6L) - from 8,000 rubles, and replacement work with refrigerant refilling will cost 5,000–10,000 rubles. For refrigerators older than 10 years, it is often more profitable to buy new equipment.