Starting a refrigerator compressor without a start relay: when is this possible and how to do it correctly

The start relay is a key element in the power supply circuit of the refrigerator compressor, which is responsible for a short-term increase in current when the motor starts. But what to do if the relay has failed and you don’t have a new one at hand? Is it possible to do without it and start the compressor directly? The answer is yes, but with serious reservations.

This method is used in extreme cases: to diagnose a compressor malfunction, temporarily restore the operation of the refrigerator, or in the absence of spare parts. However directly connecting a compressor to a 220V network without a starting relay is a risky procedure, which can lead to overheating of the windings, interturn short circuit or even fire. In the article we will look at how to do this as safely as possible, what tools will be needed and what consequences may arise.

We warn you in advance: if you do not have experience working with electricity, it is better not to experiment. Connection errors can damage the compressor beyond repair. For constant operation of the refrigerator required a working starting relay or its equivalent is required.

This article contains only proven diagrams and practical advice based on the experience of refrigeration equipment repair technicians. We will not delve into the theory of electric motors, but will focus on practice: what exactly needs to be done, which wires are connected where and how to avoid common mistakes.

When can you start a compressor without a start relay?

Direct connection of a compressor justified only in three cases:

• 🔧 Fault diagnosis: you need to check whether the compressor is working at all (for example, if the refrigerator does not turn on and the relay clicks).
• ⏳ Temporary solution: while you are waiting for the delivery of a new relay or spare part, you urgently need to save the products.
• 🔍 Check after repair: for example, if you rewound the compressor windings and need to make sure they are working.

In all other situations a starting relay is necessary. Without it, the compressor will experience increased loads at start-up, which reduces its service life significantly. This is especially critical for modern refrigerators with inverter compressors - their electronics are simply not designed for this mode of operation.

Another important point: not all compressors can be started without a relay. For example, three-phase models (found in industrial refrigerators) require special starting devices. Domestic refrigerators usually have single-phase asynchronous motors, which theoretically can be started manually.

⚠️ Attention: If your refrigerator is equipped with an electronic control unit (for example No Frost or models Samsung, LG with a display), direct connection of the compressor may damage the board. In such cases, it is better to wait for the original relay.

What tools and materials will be needed?

To safely connect the compressor without a starting relay, prepare:

• 🔌 Extension cord with grounding (preferably with an on/off button).
• 🔧 Screwdriver with insulated handle (cross or flat, depending on the fastening of the terminals).
• 📏 Multimeter (for checking winding resistance and voltage).
• 🧲 Insulating tape or heat-shrinkable tube (for insulating connections).
• 🔄 Wires with a cross-section of at least 1.5 mm² (preferably copper, stranded).
• 🛡️ Rubber gloves and mat (for protection against electric shock).

If you plan long operation of the compressor without a relay (for example, at the dacha), you will additionally need:

• 🔥 Fuse for 10–15 A (for short circuit protection).
• ⏱️ Time relay (to limit the time of continuous operation).

Critical important: never use “twists” or bare wires for connection. The contacts must be reliably insulated and the connections must be strong. even a short circuit can damage the compressor.

Connection diagram for a compressor without starting relay

Before you start connecting, you need to understand which wires go where. A typical refrigerator compressor has three terminals:

1. Common terminal (C) —connects to a 220V network.
2. Starting winding (S) —used only for starting.
3. Working winding (R) — ensures constant operation.

To start the compressor without a relay, you need short-term apply voltage to the starting winding, and then leave only the working one. This can be done in two ways:

Method 1: Manual start with a button

The simplest and safest method for a one-time test:

1. Connect common terminal (C) to the network phase (220V).
2. Connect working winding (R) to the network zero.
3. Connect briefly (for 1-2 seconds) starting winding (S) to the phase via a button or jumper.

If the compressor starts working, immediately remove the jumper from the starting winding! You cannot hold it for more than 3 seconds - this will lead to overheating.

Method 2: Through a capacitor (for long-term operation)

If you need the compressor to operate without a relay for longer than 5–10 minutes, use starting capacitor (with a capacity of 20–40 μF, voltage no less than 450V). Connection diagram:

• Common terminal (C) → phase 220V.
• Working winding (R) → zero.
• Starting winding (S) → through capacitor to the phase.

The capacitor in this case plays the role of a “soft starter”, reducing the load on the windings. However, even with it, the compressor will operate with increased wear.

⚠️ Attention: Capacitor parameters and operating time are indicated for emergency mode. Constant operation of the compressor without a starting relay reduces its life by 3–5 times.

Step-by-step instructions for connection

Now let's look at the process in detail. For example, let's take a compressor Danfoss NL35Z (one of the most common in refrigerators Atlant, Stinol, Indesit).

Step 1. Disconnect the refrigerator from networks

Unplug the plug from the socket and wait until the capacitor (if there is one in the circuit) discharges. For reliability, short-circuit the compressor terminals with a screwdriver with an insulated handle for 1-2 seconds.

Step 2. Remove the start relay

Usually it is attached to the compressor with two bolts or latches. Carefully disconnect the terminals, making note (or taking a photo) of which wires went where. There may be a connection diagram on the relay body - save it.

Step 3. Determine the compressor terminals

Take a multimeter and measure the resistance between the terminals:

• The lowest resistance (usually 5-20 Ohms) is working winding (R).
• Average resistance (20–40 Ohms) is starting winding (S).
• Total resistance (R + S, usually 30–60 Ohms) is common terminal (C).

Step 4. Connect the wires according to the diagram

Use the first method (manual start):

1. Connect common terminal (C) to the phase of the extension cord.
2. Connect working winding (R) to the zero of the extension cord.
3. Connect briefly (for 1-2 seconds) starting winding (S) with phase through an insulated wire.

Step 5. Start compressor

Plug the extension cord into the outlet and short-circuit the starting winding. The compressor should hum and begin to build up pressure. If it does not start:

• Check the reliability of the contacts.
• Make sure that the voltage in the network is not lower than 200V (at low voltage the compressor may not start).
• If the compressor hums, but does not start, it is possible piston jammed or windings are out of order.

If the compressor starts working, immediately remove the jumper from the starting winding! You cannot hold it for more than 3 seconds - this will lead to overheating.

What happens if you leave the compressor running without a relay?

Even if the compressor has started and is running, long use without a starting relay is fraught serious consequences:

• 🔥 Overheating of the windings: without a relay, the starting current can exceed the rated current by 5–7 times. This leads to insulation melting and interturn short circuit.
• ⚡ Increased energy consumption: the compressor operates inefficiently, consuming 30–50% more electricity.
• 🛠️ Accelerated wear of the piston group: due to unstable startup, the load on the mechanical parts increases.
• 💥 Risk of fire: if the insulation of the windings melts, a short circuit may occur.

According to workshop statistics, compressors operated without starting relay longer than 1 hour, fails within 1–3 months. At the same time, repairs are more expensive than buying a new relay.

It is especially dangerous to leave refrigerators with No Frost systemwithout a relay. In them, the compressor works in tandem with a fan and a defrost heater, and an unstable start can damage all electronics.

⚠️ Attention: If you notice that the compressor housing has become hot (more than 60–70°C), immediately unplug it! This is a sign of overheating of the windings.

Alternative ways to start the compressor

If there is no starting relay, but you need to start the refrigerator for a long time, consider these options:

1. Universal starting relay

Electronics stores sell universal starting relays (for example, RBM-1, DANFOSS 108N0010), which are suitable for most household compressors. They are inexpensive (from 300 to 800 rubles) and are connected according to a standard scheme.

2. Relays from other equipment

You can temporarily use a relay from:

• Old refrigerator (if the parameters match).
• Air conditioner or freezer (but you need to check current compatibility).
• Starting device for electric motors (for example, PNVS-10).

Before connecting, compare rated current the relay and the compressor (indicated on the nameplate). If the relay is designed for a lower current, it will burn out quickly.

3. Homemade relay on a thyristor

For radio amateurs: you can assemble a simple starting device on a thyristor KU202N or BTA16-600B. The circuit includes:

• Thyristor (for controlling the starting current).
• Dynistor (for turn-on delay).
• Resistors and capacitors for adjusting the response time.

However, soldering such circuits without experience is not recommended - an error in the calculations can lead to the compressor failing building.

Scheme of a homemade relay on a thyristor

For assembly you will need: thyristor KU202N, dinistor DB3, resistors 100 Ohm and 1 kOhm, capacitor 0.1 μF. The thyristor is connected to the break in the phase wire, and the control circuit is assembled in parallel with the starting circuit. winding. The turn-on delay time is regulated by a 1 kOhm resistor. Attention: before turning on for the first time, check the circuit with a multimeter for a short circuit!

Common mistakes and how to avoid them

Even experienced craftsmen sometimes make mistakes when connecting the compressor directly. Here are the most common:

• ❌ The windings are mixed up: if you connect the starting winding as a working one, the compressor will not start or will work in the opposite direction (which is dangerous for the system).
• ❌ Long-term holding of the start button: more than 3 seconds - and the winding will overheat.
• ❌ Lack of grounding: without it, the risk of electric shock due to insulation breakdown increases significantly.
• ❌ Use of thin wires: a cross section of less than 1.5 mm² may not withstand the starting current.
• ❌ Ignoring strange sounds: if the compressor knocks, creaks or vibrates strongly, turn it off immediately!

Another common mistake - trying to start the compressor without checking the pressure in the system. If there is no freon in the circuit or there is a blockage, the motor will work under increased load and will quickly fail. Before starting, make sure that:

• There is freon in the system (you can check with a pressure gauge or by sound - there should be a characteristic hissing sound when turned on). sound).
• The capillary tube is not clogged (if the compressor hums but does not start, this may be a sign of a blockage).

FAQ: Frequently asked questions about starting a compressor without a relay

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

No. Inverter compressors (installed in refrigerators Samsung, LG, Liebert) are controlled by an electronic unit, and direct connection to a 220V network will disable it. In such models, the relay is built into the control board, and it can only be replaced with a similar module.

How long can you keep the compressor turned on without a relay?

For diagnostics - no more than 5-10 minutes For temporary work (for example, to preserve food) - up to 30 minutes with a mandatory break. cooling (at least 1 hour). Longer - only with a starting capacitor and case temperature control.

Why does the compressor hum but does not start?

There are several reasons:

• The starting winding is faulty (check the resistance with a multimeter).
• The piston is jammed (you need to check whether the shaft rotates manually).
• Low voltage in the network (less than 200V).
• The pressure in the system is too high (for example, due to an excess of freon).

Is it possible to use a car relay for start?

Theoretically, yes, but you need to take into account:

• Car relays are designed for 12V, so an additional control circuit will be required.
• The contact current must be at least 10-15A (check the markings on the relay).
• It is better to use a relay with normally open contacts (for example, 90.3747).

What to do if, after direct connection, the compressor starts smoking?

Immediately disconnect it from the network! Smoke is a sign of melted winding insulation. Further actions:

1. Give allow the compressor to cool down (at least 2 hours).
2. Check the resistance of the windings with a multimeter (if it tends to zero, there is an interturn short circuit).
3. If the windings are burned out, the compressor must be replaced.