The situation when the refrigerator stops cooling, and the compressor only hums or is silent, often confuses the home handyman. In most cases, the cause of silence is starting relay, which ceases to supply an impulse to start the motor winding. Many people wonder: is it possible to start the unit bypassing this element in order to check the performance of the motor or temporarily store products before purchasing a spare part.
Technically starting refrigerator compressor directly is possible, but this requires a clear understanding of the electrical circuit and adherence to strict safety measures. Direct connection without a relay is permissible only for short-term diagnostics of the health of the windings and the mechanical part of the motor, but not for permanent operation. Continuous operation without a protective starting device threatens overheating and failure of an expensive unit.
In this manual we will analyze the design of the starting mechanism, methods for checking the integrity of the windings and the algorithm of actions for forcibly starting the engine. You will learn how to safely apply voltage to the contacts and what tools you will need to complete this procedure. It is important to understand that any work with electricity requires extreme caution.
Design and role of the starting relay in the system
The starting relay is an electromechanical switch that is responsible for supplying power to the starting winding of the engine at the time of start. As soon as the rotor reaches the required speed, the current in the circuit drops and the relay opens the contacts, turning off the starting winding. Without this mechanism, the engine will not be able to overcome inertia and begin to rotate, remaining in a humming state.
There are two main types of devices: electromagnetic and thermal (posistor). In modern models, posistor relays are most often used, which change their resistance when heated, breaking the circuit. Electromagnetic models rely on current strength: while the current is high (starting torque), the coil keeps the contacts closed, then they open. Understanding your relay type is critical to proper diagnosis. posistor relays that change their resistance when heated, breaking the circuit. Electromagnetic models rely on current strength: while the current is high (starting torque), the coil keeps the contacts closed, then they open. Understanding your relay type is critical to proper diagnosis.
If the relay is faulty, the compressor may hum but not start, or may click intermittently for a few seconds. This triggers the thermal protective relay, which turns off the power to prevent a fire. An attempt to start the motor bypassing the relay allows you to determine whether the motor itself is alive or the problem lies deeper in the electrical circuit.
⚠️ Attention: Thermal protection relay (tablet) is often built into the starter housing or located nearby. When forced to start, make sure that the overheating protection is working, otherwise the windings will burn out in a matter of minutes.
To carry out diagnostics, you will need a multimeter, pliers and insulating materials. Before starting any work, you must completely turn off the power to the refrigerator by removing the plug from the socket. Ignoring this rule may result in electric shock.
Diagnostics of the compressor before starting
Before trying to connect a refrigerator without a relay, you must ensure the integrity of the motor windings. A burnt-out motor cannot be started, and attempting to apply voltage can only aggravate the situation. The first step is always a visual inspection and “testing” of the contacts with a multimeter.
Remove the start relay and thermal protection from the compressor contacts. At the end of the motor you will see three terminals arranged in a triangle. They designate: common contact (C), working winding (R) and starting winding (S). The markings may vary depending on the manufacturer, so it is better to check the technical documentation or the diagram on the case.
Using a multimeter in resistance measurement mode, check the pairs of contacts. There must be resistance between the common terminal and the working winding, as well as between the common and starting windings (usually from 10 to 30 Ohms). Between the starting and working windings the resistance will be total. If the device shows infinity, there is a break; if zero, there is a short circuit.
It is also important to check whether the motor is “breaking through” the housing. Press one multimeter probe to any contact, and the second to the place on the compressor housing that has been cleared of paint. The device should not show any conductivity. The presence of resistance between the winding and the body indicates a fatal malfunction.
| Pair of contacts | Normal resistance (Ohm) | Possible malfunction |
|---|---|---|
| Common - Working | 10 – 25 Ohm | Open or short winding |
| General - Starting | 20 - 40 Ohm | Open or short winding |
| Working - Starting | The sum of the two is higher | Violation of circuit integrity |
| Any - Housing | Infinity (∞) | Insulation breakdown on the housing |
If all measurements are normal, you can proceed to try to launch. However, remember that the lack of resistance on one of the windings makes further attempts pointless - the compressor needs to be replaced.
Connection diagram and contact marking
To successfully start the motor, it is necessary to correctly identify the contacts. On most compressors, such as Atlant, Danfoss or Secop, the pins are arranged in a certain order. Usually the common contact is located separately, and the starting and working windings are located nearby. However, relying only on location is dangerous. Atlant, Danfoss or Secop, the conclusions are arranged in a certain order. Usually the common contact is located separately, and the starting and working windings are located nearby. However, relying on location alone is dangerous.
The most reliable way to identify contacts without a diagram is to measure the resistance. The greatest resistance will be between the starting and working windings. The average value will indicate the starting winding (relative to the total), and the smallest value will indicate the working winding. This is a basic principle of electrical engineering that works for most asynchronous motors.
Wire color marking table (may vary)
Usually a red or brown wire goes to the starting winding, blue or black to the working winding, but the colors may differ in different models of refrigerators. Always rely on resistance measurements, not on the color of the insulation.
When preparing to connect without a relay, you will have to simulate the operation of the starter. This means that you need to briefly apply voltage to the starting winding, and then leave power only on the working winding. This must be done quickly and carefully, using an insulated tool.
There is a starting method using a capacitor, which is often used by craftsmen. The capacitor is connected in parallel with the starting winding at the time of start, creating the necessary phase shift. The capacity is selected experimentally, but for household refrigerators 10-20 uF with a voltage of at least 250V is usually enough.
Instructions: how to start a compressor directly
The process of starting a compressor bypassing the standard relay requires a working power cord with a plug and, preferably, a breaker button or toggle switch for convenience. The main task is to supply 220 Volts to the common and working contacts, and “push” the starting contact with a short-term impulse.
Prepare two wires with stripped ends. One wire (phase) will be connected to the working contact permanently, the second (starting) - to the starting contact temporarily. The neutral wire is connected to the common terminal of the compressor. Before turning on, make sure that the wires do not touch each other and the housing.
☑️ Safe start of the compressor
Plug the plug into the socket. The compressor will not start because the starting winding circuit is open. Now gently touch the wire to the trigger contact. The engine should hum and start. As soon as the rotor picks up speed (after 1-2 seconds), the starting wire must be removed immediately.
If the engine hums but does not start, the piston mechanism may be jammed or there is not enough starting torque. In some cases, briefly connecting a starting capacitor in parallel with the starting winding at the moment of start helps. This creates additional torque.
⚠️ Attention: Do not keep the start contact closed for more than 3 seconds! This will cause the starting winding to overheat and may cause a short circuit or fire.
After successful startup, let the compressor run for a couple of minutes, monitoring the housing temperature and noise level. If the motor runs smoothly and gains pressure (checked by touch on the output tube), then the problem was in the relay.
Risks and limitations of operation without a relay
Using a refrigerator without a standard starting relay is only possible in emergency mode for a short time. The absence of automatic shutdown of the starting winding leads to its rapid overheating. In normal mode, the relay opens the circuit immediately after start, protecting the turns from burnout.
In addition, the standard relay is often combined with thermal protection. By operating without it, you leave the engine without a "fuse". If there is a power surge or the piston jams, the motor will burn out, since the thermal relay will not break the circuit. This turns diagnostics into expensive repairs.
Another risk is associated with startup instability. The standard relay was selected by the manufacturer specifically for the characteristics of this motor. Manual starting or using a capacitor does not guarantee the correct phase shift, which reduces the efficiency and life of the compressor.
It is also worth considering that modern inverter compressors cannot be started in this way. They require sophisticated speed control electronics. The described methods are applicable only to classic asynchronous motors.
Replacement of the relay and final assembly
After successful diagnosis and confirmation of the serviceability of the compressor, the only correct solution is to install a new starting relay. This is an inexpensive part that will ensure reliable and safe operation of the refrigerator for many years. The selection of an analogue is carried out according to the compressor model or the marking of the old relay.
Take readings from the compressor nameplate (model, power, refrigerant) and go to a spare parts store or place an order online. Install the new relay on the contacts until a characteristic click is heard, put on the thermal protection and secure the fixing bracket or bar.
Plug in the refrigerator. A working unit should start the first time, the relay will click after 1-2 seconds, and the cooling process will begin. If the clicks are repeated, but the cold does not come, the relay may be selected incorrectly or the problem is in the motor itself.
⚠️ Attention: The characteristics of the starting relays may differ even for outwardly identical models. Always check the markings and contact orientation (up, down or sideways) before installation.
Do not forget that after any intervention in the electrical part or the refrigerant system, time is required for pressure and temperatures to stabilize. Do not load the refrigerator with food immediately, let it go into operation for several hours.
Frequently asked questions (FAQ)
Is it possible to leave the refrigerator to work without a relay all the time?
It is strictly not recommended. Without a relay, the starting winding will be energized for too long, causing it to overheat and burn out. In addition, the lack of thermal protection can cause a fire.
What kind of capacitor is needed to start the compressor?
Usually starting capacitors with a capacity of 10 to 50 μF with an operating voltage of at least 250-450 Volts are used. The exact capacity depends on the engine power and is selected experimentally or according to reference data.
Why does the compressor hum, but does not start even with a relay?
There may be several reasons: jamming of the piston group (compressor), an interturn short circuit in the windings, low voltage in the network, or a malfunction of the relay itself. Complex diagnostics are required.
Is it dangerous to touch the wires when the compressor is running?
Yes, it is deadly. The network voltage is 220 Volts. All manipulations with live wires should be carried out only by qualified specialists using dielectric gloves and tools.
How much does it cost to replace a starting relay?
The cost of the relay itself varies from 500 to 1500 rubles, depending on the model and manufacturer. The services of a replacement technician can cost an additional 1,000 rubles, although the replacement process takes a few minutes.