Sometimes, in the process of diagnosing malfunctions of refrigeration equipment, there is an urgent need to check the performance of the motor by disconnecting it from the standard control system. Starting the compressor without the participation of a start-up relay, it may be necessary to identify the cause of a breakdown when the device hums but does not start, or when there is an urgent need to freeze food, and a new relay has not yet been delivered. This is an emergency measure that requires strict adherence to electrical safety rules and a clear understanding of the operating principles of the electric motor.
In normal operation mode starting relay supplies current to the starting winding for only a fraction of a second, after which it turns it off, leaving only the main winding to work. Ignoring this principle during direct connection can lead to overheating of the windings and failure of the unit. Therefore, before deciding to start directly, you need to make sure that the problem lies precisely in the control electronics, and not in the motor itself.
This procedure allows you to isolate the fault and understand whether it is alive unit or the problem is in the control circuit. However, it should be remembered that long-term operation of the motor without thermal protection and proper switching of windings is unacceptable. Below we will analyze in detail the technical nuances, the necessary tools and a step-by-step algorithm of actions for safe diagnostics.
The principle of operation of a single-phase electric motor
To competently start refrigeration compressor bypassing standard systems, you need to understand the internal architecture of the electric motor. Most household refrigerators are equipped with single-phase asynchronous motors, which have two main windings: working (main) and starting. The working winding occupies most of the stator slots and is designed to create the main magnetic flux during operation.
The starting winding is made of thinner wire and has greater electrical resistance. Its task is to create the initial torque necessary to break the rotor from its place. In the standard circuit starting relay (often electromechanical) it closes the starting winding circuit at the moment of switching on, and then opens it when the engine reaches the required speed. If the relay is faulty, the starting winding circuit may not close at all, and the motor will only hum without starting to rotate.
Why does the motor hum but not spin?
The hum indicates that electric current enters the working winding and creates a magnetic field, but the torque is not enough to overcome the inertia and freon pressure. Without an impulse from the starting winding, the rotor remains motionless, which causes a characteristic low-frequency hum and rapid heating.
With direct connection, our task is to artificially simulate the operation of the relay by applying voltage to the starting winding only at the time of start. Capacitorif it is present in the circuit (in some models, instead of a relay, capacitor starting is used), it serves to shift the phase, which also helps create torque. Ignoring the phasing or timing of the pulse may result in the shaft starting to rotate in the opposite direction or the motor burning out.
Necessary tools and precautions
Before you begin to manipulate the 220 volt electrical circuit, you must prepare the appropriate tools and ensure safety. Working with high voltage and refrigerants requires care. You will need a multimeter to check the integrity of the windings, insulated wires with crocodile clips, a screwdriver and, possibly, a button for briefly closing the circuit.
⚠️ Attention: It is strictly forbidden to carry out work on connecting the compressor while the power cord is plugged in. All wiring connections should be made only with the system completely de-energized to avoid electric shock.
It is also important to prepare the work area. The compressor should be installed on a flat surface, preferably in the same position as it was in the refrigerator (usually vertically on rubber feet). This is necessary for the correct operation of the oil system, although during short-term diagnostics it is less critical than during long-term operation.
- 🛠️ A multimeter or tester for checking the windings and checking the resistance.
- 🔌 Two insulated wires with terminals for connecting to the network and motor contacts.
- 🔘 A button or switch for briefly applying a pulse to the starting winding.
- 🧤 Dielectric gloves and tools with insulated handles to protect your hands.
Make sure that the surrounding area is dry and free of flammable materials, as in the event of an insulation breakdown or oil leakage, it may occur sparking. Electrical safety is priority number one, so do not neglect the use of protective equipment.
Diagnostics of windings before starting
Before attempting to start the motor, you must ensure the integrity of its internal components. The first step should always be a visual inspection and test of the windings using a multimeter. There are usually three terminals located on the contact field of the compressor: common (Common), working (Run) and starting (Start). Their markings may differ depending on the manufacturer, for example Denso, Secop or Atlant.
Using a multimeter in resistance measurement mode (Ohm), it is necessary to measure the resistance between each pair of contacts. The sum of the resistances between pairs of contacts should give the total resistance of the circuit. For example, if the resistance between general and working is 20 Ohms, and between common and starting is 50 Ohms, then the resistance between working and starting should be about 70 Ohms.
☑️ Checking the compressor before starting
If the multimeter shows infinity (open) or zero (short circuit) between the terminals, start such a unit pointless and dangerous. Also be sure to check the resistance between any terminal and the copper tube or motor housing - there should be no conductivity there. The presence of resistance to the housing indicates an insulation breakdown, which makes further operation impossible.
Scheme of direct connection to a 220V network
To implement start-up without a relay, a circuit is used where 220V voltage is supplied directly to the working terminal and the common terminal. The trigger pulse is supplied manually or via a button to the trigger output. It is important to correctly identify the contacts: the common wire (C) often has the largest cross-section or is located separately, but an accurate determination is only possible by resistance measurements or markings on the diagram pasted on the case.
Connect one wire from the network to the common contact, and the second wire to the working contact of the winding. At this moment, the engine will not start, but will only hum. To start it, you need to briefly (for 1-2 seconds) close the starting contact with the working or common wire (depending on the circuit of a particular motor, most often the starting winding is powered relative to the common wire). After starting the motor, the starting circuit must be immediately broken.
| Contact type | Designation on the diagram | Wire color (often) | Resistance |
|---|---|---|---|
| Common | C / COM | Black / White | Basic zero reference |
| Run | R | Red / Green | Low (10-30 Ohm) |
| Start | S | Yellow / Blue | High (30-80 Ohm) |
| Ground (case) | GND | Yellow-green | Infinity |
Some craftsmen use a capacitor with a capacity of 4-6 uF to facilitate starting, connecting it in parallel starting winding at the time of start. However, for a simple diagnosis of the performance of the motor, a manual impulse is often sufficient. The main thing is not to keep the starting winding energized for more than 3-5 seconds to prevent it from overheating.
Starting process and testing
After checking the diagram and preparing the tools, you can move on to the practical part. Plug the plug into the outlet (being careful!). If the motor is working properly and connected to the working winding, you will hear a smooth hum. At this moment, it is necessary to briefly apply an impulse to the starting winding. If everything is done correctly, you will hear a click (if a button is used) and the characteristic sound of the engine picking up speed.
The motor should start running smoothly, without strong vibration or extraneous knocking. The pressure at the outlet of the discharge tube should be felt by hand (be careful, the air stream may be hot and contain oil vapor). If the motor started, but after a few seconds there was a click and it stopped, the internal thermal protection may have worked, if it survived, or the motor has jammed.
⚠️ Attention: The time of continuous operation of the compressor in diagnostic mode should not exceed 5-10 minutes. Without proper cooling and circulation of freon, the motor can quickly overheat, which will lead to deformation of the valves or jamming of the piston group.
During the test, carefully monitor the body temperature. If it becomes too hot to touch with your hand in a short time, turn off the power immediately. Also pay attention to the color of the escaping air: if black oil flies out along with the air or a burning smell is felt, the compressor requires replacement or serious repairs.
Possible problems and their solutions
During the diagnostic process, various situations may arise that require an immediate response. If the motor hums but does not start even when an impulse is applied to the starting winding, a mechanical wedge of the piston group is likely. In some cases, the so-called “kick method” helps - applying voltage to the starting winding at the moment the power is turned on, but this rarely works and does not guarantee success.
If the motor starts, but is very noisy or knocks out the circuit breaker in the panel, this may indicate an interturn short circuit in the windings. In this case, further operation is impossible, since such a motor is a fire hazard. Also a common problem is the lack of pressure, which indicates a breakdown of the valve system, even if the shaft itself rotates.
- 🔥 The motor heats up in 1-2 minutes - a sign of an interturn short circuit or lack of lubrication.
- 🔇 Complete silence when voltage is applied - an open circuit inside the motor or lack of contact.
- 💨 There is no pressure at the outlet when the engine is running - destruction of the valves or piston group.
- ⚡ Knocks out the plugs - short circuit in the windings or wiring.
It is important to understand that starting without a relay is a temporary diagnostic measure. It is impossible to operate the refrigerator in this mode all the time, since the lack of protection will lead to the motor burning out at the slightest voltage surge or increase in pressure in the system. After diagnostics, be sure to install a new one that matches the relay model.
Frequently asked questions (FAQ)
Is it possible to leave the refrigerator running without a start relay all the time?
No, this is strictly prohibited. Without a relay, the starting winding will either not receive an impulse to start, or (if switched incorrectly) will burn out from overheating. In addition, the lack of thermal protection will lead to a fire if the motor is jammed.
What capacitor is needed to start the compressor?
Usually starting capacitors with a voltage of at least 450V and a capacity of 4 to 10 µF are used, depending on the power of the motor. The exact parameters are indicated in the technical documentation for the specific refrigerator model.
Why does the compressor hum but does not start?
The most likely reasons: a malfunction of the starting relay, a break in the starting winding or a mechanical wedge of the piston group (scuffing, lack of oil, frozen moisture in the system).
Is it dangerous to carry out such manipulations yourself?
Yes, working with 220V voltage is life-threatening. In addition, improper handling can lead to depressurization of the cooling system and release of refrigerant. If you do not have the skills of an electrician, it is better to call a specialist.
How to determine whether the compressor or relay has burned out?
You need to test the windings with a multimeter. If the resistance of the windings is normal and there is no breakdown to the housing, and the motor does not start when voltage is directly applied, most likely the problem is in the relay. If the windings show a break or short circuit, the motor is burned out.