The situation when the refrigerator stops cooling, and the compressor is silent or makes only a short beep, often confuses the owner. In most cases, the cause is a failure of the start-up relay, which is responsible for starting the engine. However, there are times when you need to start the unit directly, for example, to check the performance of the motor itself or as a temporary measure before purchasing a spare part. Connecting the compressor directly - a procedure that requires strict adherence to safety precautions, since the work is carried out with a mains voltage of 220 volts.
Before starting manipulations with electrical wiring, it is necessary to clearly understand that excluding the relay from the circuit deprives the motor of protection from overheating and overloads. Start relay it does not just close the contacts, it provides the necessary phase shift to start the rotor and opens the starting winding circuit after gaining speed. If you ignore these functions, you may burn the windings or cause a fire. Therefore, this method is used exclusively for diagnostics or short-term starting.
In this article we will look in detail at how to safely apply voltage to the motor contacts, what tools will be needed and how to distinguish a working compressor from a burnt one. You will learn why the light in the circuit blinks and what to do if the engine hums but does not start.
The design of the starting mechanism and the role of the relay
To understand the “direct” starting process, you need to know how the standard circuit works. The refrigeration unit motor has two windings: working and starting. The working winding creates the main magnetic field, and the starting winding is needed only at the moment of start, in order to give the rotor initial rotation. Starting relay automatically supplies current to the starting winding at the moment of switching on and turns it off when the engine reaches about 75% of the rated speed.
In addition to the starting function, the unit often contains a thermal protection relay. It responds to the amount of current flowing through the motor. If the compressor is jammed or overloaded, the current increases, the bimetallic strip heats up and opens the circuit, preventing the insulation from melting. When connecting directly, you remove this fuse, taking control of the process.
⚠️ Attention: Working without a thermal relay means that when the piston group jams, the engine will hum until the winding burns out or the machine in the panel is knocked out. Do not leave the refrigerator turned on in this way unattended for even a second.
Modern inverter models may have a different device where the start is controlled by an electronic module. In such cases, the "direct connection" method to the terminals may not work or damage the electronics. Make sure your unit is equipped with a classic asynchronous motormotor with a starting winding.
Required tools and safety precautions
Safety is the number one priority when working with high voltage. You will need a minimum set of tools that most home craftsmen will have. The main requirement is the insulation of all live parts that you may accidentally come into contact with.
For work, prepare:
- 🔌 A piece of wire with a plug and terminals for connecting to the network.
- 🔧 A set of screwdrivers (flat and Phillips) for removal casing.
- ✂️ Side cutters or a knife for stripping wire insulation.
- 🧤 Dielectric gloves (preferably) and dry shoes with rubber soles.
- 💡 Test lamp or multimeter to check the presence of voltage.
Be sure to unplug the power cord before touching any internal components. Even capacitors in the circuit can retain a charge, so let the unit stand for 5-10 minutes after turning it off. Capacitor (if it is in the circuit) can give an electric shock if you close its contacts with a screwdriver.
You should work in a well-lit place where nothing interferes with movements. Wet floors or metal surfaces near the workplace are not permitted. If you use a test lamp to check, be careful: the bulb may break and the spiral may burn out during a power surge.
☑️ Safety check before starting
Diagnostics: why the relay could fail
Before connecting the wires directly, it is worth understanding that exactly what happened. Often, owners try to start the engine bypassing the relay, thinking that it has burned out, although the problem may be deeper. Symptoms of a malfunction can be different: complete silence, humming without starting, or periodic clicks.
The main signs of problems with the starting mechanism:
- 🔊 The compressor hums for 3-5 seconds, then a click is heard and there is silence.
- 🔥 The relay housing is strong heats up or has a burning smell.
- ⚡ When you shake the removed relay, a ringing is heard (the internal tablet or contacts have collapsed).
- 🌡️ The thermal relay constantly turns off the engine at short intervals.
If, with a direct connection, the engine starts and runs smoothly, but without the relay stalls when turned on again - the problem is 100% in the starter. However, if the motor hums and does not spin even with a direct connection, the mechanical part or interturn short circuit may be jammed.
| Symptom | Probable cause | Reaction with direct connection |
|---|---|---|
| Clicking and silence | Starting relay burnt out | Starting (if the motor is working) |
| Humming and heating | Compressor jamming | Humming, knocking out plugs |
| No reaction | Breakage of winding or thermal relay | No reaction |
| Protection activation | Short circuit | Sparks, smoke, shutdown automatic machine |
It is important to distinguish between these states, since an attempt to “unwedge” a frozen compressor by applying increased voltage or holding the starting winding for a long time can finally finish off the unit. Interturn short circuit often manifests itself in the fact that the engine starts, but very quickly and heats up very quickly.
Connection diagram: contact identification
The most critical stage is identifying the contacts on the compressor block. Different manufacturers (Atlant, Indesit, Bosch) may have different pin locations, but the principle is the same. On the terminal block there are usually three contacts forming a triangle, and one separate one (often marked with ground).
You need to find three working terminals:
- Common — phase or zero (depending on the circuit) goes to it.
- Start winding (Start) —has a higher resistance.
- Working winding (Run) —has a lower resistance.
To identify them without marking (if it is erased), use multimeter in resistance measurement mode. Measure the resistance between each pair of contacts. The greatest resistance will be between the starting and working windings. The third contact, left “overboard” from these measurements, or the one where the sum of the resistances of the other two pairs gives the resistance of the third, is the common one.
⚠️ Attention: Never rely solely on the color of the wires coming from the old relay. The previous master could have confused them. Always double-check the resistance of the windings with a multimeter.
Typical resistance values for a working average power compressor: between operating and general - 10-20 Ohms, between starting and general - 20-40 Ohms. If the device shows one (infinity), the winding is broken. If zero - short circuit.
Wire color matching table (conditionally)
Usually black or brown - general, red or blue - starting, white or yellow - working. But colors may vary depending on the relay manufacturer and year of manufacture!
Step-by-step instructions for direct launch
Once the contacts have been identified, you can begin assembling the temporary circuit. The essence of the method is to apply voltage to the common and working windings constantly, and to the starting winding only at the moment of start.
Action algorithm:
- Connect one wire from the plug (for example, zero) directly to the contact General on the compressor. Use a reliable twist, insulated with electrical tape, or a terminal block.
- Connect the second wire from the plug (phase) to the contact Working winding.
- To start you will need the third wire (button or just an insulated piece of cable). Connect one end of it to Start winding.
- Plug the plug into the socket. The compressor will not stand still.
- Briefly (for 1-2 seconds) touch the free end of the third wire to the contact Working winding (where the phase is already connected).
If the motor is working, it should start and continue to work after you remove the wire from the starting winding. At this moment, current flows only through the working winding. It is important not to keep the starting winding on for more than 2-3 seconds, otherwise it will burn out, since it is not designed for long-term operation.
There is also a circuit using a capacitor, which simulates the operation of a relay, creating a phase shift. However, for one-time diagnostics, the method of “manually” closing the starting winding is the simplest and most understandable.
Analysis of results and possible problems
After starting, listen carefully to the operation of the unit. A smooth hum, absence of metallic knocks and gradual cooling of the evaporator indicate success. However, other scenarios may arise that require analysis.
If the compressor hums, but does not start even with the “help” of the starting winding, a hydraulic wedge is likely. The piston group may have frozen due to thickened oil or mechanical damage. In such cases, sometimes the method of “tapping” or applying voltage to all three contacts at once helps (the method is risky and requires experience), but most often this is a sign of the demise of the compressor.