How to start a refrigerator without a starting relay: diagnostics and direct connection

The situation when a household refrigerator suddenly stops cooling, and the compressor only hums or clicks, but does not start, is familiar to many equipment owners. Most often, the cause is the failure of start relay a small but critical unit responsible for starting the engine. In such cases, the master or owner is faced with the question: is it possible to start the unit bypassing this element in order to check the performance of the motor or temporarily store products?

Starting the compressor directly, bypassing the standard control circuit, is a common method diagnosticsto determine whether the engine itself is alive or the problem lies deeper. However, it is worth understanding that operation without a relay is an emergency measure, and not a normal mode of operation. Induction motorinstalled in most refrigerators requires the creation of a rotating magnetic field, which cannot occur without a starting winding and appropriate current phase switching.

In this article we will analyze in detail the technical nuances of such a connection, the action plan and, most importantly, security measures. Ignoring the rules for working with high voltage and thermal stress can result in expensive equipment failure or personal injury. Therefore, before taking up the tools, it is necessary to clearly understand the principle of operation the electrical circuit of the refrigeration unit.

The main task when starting without a relay is to manually or with the help of auxiliary devices to simulate the operation of the starting winding, which should turn on for a short time and turn off after the rotor picks up speed. If this is not done, the windings will overheat and the engine will burn out. Direct connection of the windings without a timer for turning off the starting circuit is guaranteed to lead to the engine burning out in a matter of seconds.

The principle of operation of the starting relay and the need for its presence

To understand how to bypass the relay, you need to know that it does. Classic refrigerators use single-phase asynchronous motors with a starting winding. This design has one working winding, which creates a pulsating magnetic field, which is insufficient to independently start the rotor from a stationary state. To start rotation, a second force vector is required, which is created starting winding.

The starting relay performs the function of a circuit breaker. At the moment of switching on, it supplies voltage to the starting winding. As soon as the rotor reaches about 75% of the rated speed, the relay (mechanical or electronic) opens the starting winding circuit, leaving only the main winding running. If the relay is faulty and does not open the circuit, the starting winding, designed for short-term operation, burns out.

⚠️ Attention: Operating the engine without a relay is only possible if you artificially create an open circuit in the starting winding 1-3 seconds after start. Constant supply of voltage to the starting winding is unacceptable.

There are several types of relays, and understanding their differences is important for diagnostics:

• 🔹 Thermal (induction): they use heating of a bimetallic plate with current to open the contacts.
• 🔹 Posistor: use the property of a posistor to sharply increase the resistance when heated, essentially turning off the winding.
• 🔹 Electromagnetic: open the circuit when the current drops in the working winding after spinning up the rotor.

When you try to start without a standard relay, you take over the functions of this circuit breaker. This requires precise timing and understanding of the processes occurring inside the motor Danfoss, Secop or Atlant. Any mistake in switching time can cost you a new compressor.

Why does the starting winding burn out?

The starting winding is made with a wire of a smaller cross-section and has fewer turns than the working one. It is not intended for long-term operation under load. If current continues to flow to it after the engine starts, the resistance quickly increases, the insulation melts, and a short circuit or open circuit occurs.

Required tools and safety precautions

Before starting any work on the electrical part of the refrigerator, it is necessary to ensure maximum safety. The work is carried out with a mains voltage of 220 Volts, which poses a real threat to life. In addition, incorrect actions can damage the insulation of the wires or cause a short circuit in the apartment's network.

To carry out diagnostics and temporary startup, you will need a set of tools:

• 🔧 Multimeter: for testing the windings and checking the integrity of the circuits.
• 🔌 Cord with plug: for supplying power directly to the compressor contacts.
• 🛠 A set of screwdrivers and pliers: for dismantling the casing and removing the old relay.
• 🧤 Dielectric gloves: required when working under voltage.

It is also important to prepare insulating materials, such as electrical tape or heat shrink, to prevent accidental contact with live parts. If you plan to use a button to simulate the operation of a relay, it must be designed for a current of at least 10-15 Amps, since the starting current of the motor significantly exceeds the operating current.

Pay special attention to the condition of the wires going to the compressor. Often due to vibration and heat, the insulation on them cracks. Before applying voltage, make sure that there are no exposed areas that could touch the metal body or copper tube of the refrigerator.

Diagnostics: checking the compressor windings with a multimeter

Before you try to start the engine, you need to make sure that the problem is in the relay, and not in the compressor itself. If the motor windings are burned out or shorted to the housing, no relay will help, and starting directly will only kill the unit. Diagnostics begins with a visual inspection and continuity testing of the contacts.

Remove the protective casing and disconnect the starting relay along with the capacitor (if any). The compressor terminals usually have three contacts forming a triangle. You need to determine which one corresponds to the working winding, which one corresponds to the starting winding, and which one is common. To do this, use a multimeter in resistance measurement mode (Ohms).

Algorithm for dialing:

1. Find the pair of contacts with the highest resistance - this is the sum of the resistances of both windings.
2. The third contact, which remains free, will be common.
3. Measure the resistance between the common contact and the other two.
4. The winding with lower resistance is the working winding, and the one with higher resistance is the starting winding.

Normal resistance values for household refrigerators vary in the range from 10 to 30 Ohms for the working winding and from 30 to 50 Ohms for starting. The exact numbers depend on the motor power and manufacturer, for example, for models Indesit or Bosch they may differ.

Also be sure to check that there is no breakdown in the housing. Press one multimeter probe to the cleaned area on the compressor housing (where there is no paint), and touch each of the three contacts with the other. The device should show infinity. If there is at least some resistance value, such a refrigerator cannot be operated - this is an electric shock through metal shelves or products.

Direct connection diagram: step-by-step instructions

If the diagnostics showed that the windings are intact, you can proceed to a test run. The essence of the method is to apply voltage to the working winding and briefly connect the starting winding. To carry out this process manually, you will need the help of a second person or the use of a locking button.

Prepare a power cord with a plug. Strip the ends of the wires. One wire (phase) will be connected to the common contact of the compressor permanently. The second wire (zero) will switch between the working and starting windings, or be supplied to the working winding permanently, and to the starting winding briefly through a button. Let's consider the most common and safe option with a button.

Procedure:

• 🔹 Connect the phase wire of the network to general the compressor contact.
• 🔹 Connect the neutral wire of the network to the contact working winding.
• 🔹 Take an additional piece of wire with a button (or just a stripped end for a short-term circuit).
• 🔹 Connect one end of this wire to the neutral wire of the network (parallel to the working winding).
• 🔹 With the other end, touch the contact starting winding.

The moment you touch the starting contact, the engine should hum and start. As soon as you hear a confident, even hum and see that the rotor has spun (usually after 1-2 seconds), the starting winding circuit must be broken immediately. The engine will continue to operate on the working winding.

⚠️ Attention: Do not keep the starting winding connected for more than 3 seconds! This is a critical time, after which irreversible overheating and destruction of the insulation of the starting coil begins.

After a successful start, you can connect a capacitor (if it is provided by the design of your motor type) in parallel with the starting winding to improve performance, but for short-term diagnostics this is not necessary. The main thing is to make sure that the compressor picks up speed and begins to pump freon (checked by heating the condenser or vibration of the tubes).

Use of a universal relay and push-button start

Manual start control is inconvenient and dangerous, therefore, for temporary operation or testing, universal starting relays or push-button stations are often used. A universal relay (for example, the PZR type or its modern analogues) is suitable for many models of compressors and automatically performs the function of disconnecting the starting winding.

Installation of a universal relay is simple: it is placed directly on the contacts of the compressor. However, it is important to select a relay for the power of your engine. The relay body indicates the power range in watts or horsepower (hp). If you place a relay from a powerful refrigerator on a small one, it may not work, and the starting winding will burn out.

An alternative option is to use a control button without latching (like on a doorbell) or with self-reset. The circuit is assembled like this:

Network (Phase) --> Common compressor contact
Network (Zero) --> Working winding (permanent)
Network (Zero) --> Button --> Start winding (short-term)

By pressing the button, you supply current to the starting winding. By letting go, you open the circuit. This method allows you to control the starting process more accurately than with an automatic relay if it is not selected correctly. However, it requires the constant presence of an operator.

It is worth noting that for compressors with increased starting torque (labeled LBP or HBP), using a simple button may not be sufficient, since a significant current is required to break the rotor from its place. In such cases, it is better to use specialized starting devices or high-capacity capacitors.

Typical errors and risks when starting directly

An attempt to revive a refrigerator without a relay is associated with a number of risks that you need to know about in advance. The most common mistake is keeping the starting winding energized. Even a few extra seconds can lead to thermal destruction of the varnish coating of the wires inside the stator.

Another common mistake is confusion in the contacts. If you mix up the working and starting windings when connected directly, the engine may hum, but not start, or start in the opposite direction (which does not matter for a refrigerator piston compressor, but will create an emergency operation). In the worst case, this will lead to instantaneous combustion of the winding with less resistance.

Main risks:

• 🔥 Fire: sparking of contacts or overheating of wires can ignite insulation or plastic elements.
• 💥 Compressor explosion: with a wedge piston group and attempts to start, the current increases many times, which can lead to depressurization of the housing.
• ⚡ Electric shock: when operating without proper insulation and grounding.

⚠️ Attention: If after when starting, the compressor is too loud, knocks or heats up quickly (more than 80-90 degrees), turn it off immediately. Operation in this mode will lead to jamming.

Also, after turning off the power, the compressor should cool down and the pressure in the system should equalize (usually 5-10 minutes). Frequent switching on "in sales" (at high pressure in the system) creates a colossal load on the shaft and can break the connecting rod or piston.

What is a thermal protection relay?

This is a separate element (often combined with a starting one) that opens the circuit in case of overcurrent or overheating. By starting the refrigerator directly, you often bypass this protection, leaving the motor defenseless against power surges and overheating.

Frequent questions and answers (FAQ)

Is it possible to leave the refrigerator running without a relay all the time?

No, this is impossible and dangerous. Without a mechanism to turn off the starting winding, it will burn out in a few minutes or even seconds. For permanent operation, it is necessary to install a new standard or universal relay.

Why does the compressor hum, but does not start even with the relay?

Probable reasons: jamming of the piston group (the compressor is stuck), an interturn short circuit in the windings, low voltage in the network or a malfunction of the relay itself (burnt contacts). Diagnostics with a multimeter and checking the current consumption are required.

How to determine which wire goes where if the markings are erased?

Use a multimeter. The resistance between the common and operating points is always less than between the common and starting points. The third pair (working-starting) gives the sum of resistances. You can also be guided by the location of the contacts on the block, but continuity is more reliable.

Is it dangerous to touch the body of a running compressor when starting this way?

Yes, it is dangerous. When making a homemade connection, the ground loop is often broken. In addition, if there is a breakdown of the insulation of the windings on the housing (which often happens in old motors), there will be a potential of 220V on the housing. Always use dielectric gloves.

How long can you operate a refrigerator with a button instead of a relay?

Only in emergency mode for checking or short-term preservation of food (several hours). Continuous operation is unacceptable due to the lack of thermal protection and the risk of human error when turning on the starting winding.