In situations where the refrigerator suddenly stops freezing, and diagnostics indicate a faulty electronics or starting relay, before the owner is faced with the question of checking the serviceability of the very heart of the unit. Starting the refrigerator compressor directly - this is a standard procedure for experienced craftsmen, which allows you to exclude engine breakdown from the list of potential problems. If the motor hums, but does not start, or is completely silent, a direct connection to the network will help you understand whether the unit is alive or it’s time to dispose of it.
However, you should immediately warn: working with high voltage electric current requires extreme concentration and compliance with safety precautions. Incorrect actions can lead not only to the failure of expensive equipment, but also to electric shock. In this article, we will analyze in detail the design of the starting mechanism, consider connection diagrams for various types of engines and determine in which cases independent starting is justified.
Before taking up the tools, you need to clearly understand what type of engine you are dealing with. Modern and old models can differ significantly in the design of the starting group, and there is no universal method “for everyone.” Inverter compressors, for example, it is generally impossible to start directly without a special control unit, which beginners often forget about. We will focus on classic asynchronous motors, which make up the majority of household appliances.
Design and principle of operation of the compressor
To safely manipulate the electrical part, you need to understand the internal architecture of the unit. Classic piston compressor is a sealed metal tank, inside of which there is an electric motor and a pumping group. There are three contact pins on the case, which are key to starting. It is through them that voltage is applied to the stator windings, creating a magnetic field that rotates the rotor.
The difference between the models lies in the number and type of windings. The standard circuit uses a working winding, which occupies most of the stator slots, and a starting winding, which has less resistance and is located at an angle of 90 degrees to the working one. The starting winding is turned on only at the time of start (1-3 seconds), after which it must be immediately turned off, otherwise the engine will burn out. The starting relay or electronic circuit is responsible for this shutdown.
There are also motors with capacitor starting, where a capacitor is used to create a phase shift. In such models, the starting winding can remain connected permanently or can be turned off by a centrifugal switch. Understanding your motor type is critical as the voltage supply to capacitor motor will differ from that of a motor with a start relay.
⚠️ Warning: There is oil inside the compressor and the contacts may spark. During a long test run (more than 1 minute) without a standard cooling system (condenser tubes), the housing can become very hot, and the outlet pressure can create a dangerous stream of air.
Necessary tools and safety measures
Preparation of the workplace is the key to successful diagnosis. You will need a minimum set of tools that any home mechanic who repairs equipment will have. The main thing is to ensure the insulation of all connections, since 220 Volts are deadly. Do not neglect the use of dielectric gloves and tools with insulated handles.
To carry out work using the direct connection scheme, you will need:
- 🔌 A working power cord with a plug and an alligator clip for grounding.
- 🔧 A set of screwdrivers and side cutters for stripping wires.
- 🧤 Dielectric gloves and safety glasses.
- 💡 Incandescent lamp (power 100-150 W) for sequential connection in the circuit.
- 📏 Multimeter for checking the resistance of the windings.
Using an incandescent lamp in an open circuit is a professional life hack that allows you to protect the compressor and wiring. If a short circuit occurs in the engine, the lamp will light up at full intensity, limiting the current and preventing plugs from blowing out or a fire. If the engine is working properly, when starting, the lamp may flash briefly and then glow dimly or go out, depending on the load.
It is strictly forbidden to carry out connection experiments in a damp room or standing on a wet floor. Make sure that the power cord that you use to supply 220V does not have any damage to the insulation. Grounding The compressor housing (if it is metal and not insulated from the frame) is also a mandatory electrical safety requirement.
Contact identification windings
The most difficult stage for a beginner is to figure out which of the three pins protruding from the housing is the beginning of the working winding, which is the starting winding, and which is the common wire. On old Soviet refrigerators, markings could be applied to the block, but in modern units it is often necessary to use the dialing method. On the case next to the contacts there may be letters: C (Common) - common, R (Run) - working winding, S (Start) - starting.
For an accurate determination, use a multimeter switched to resistance measurement mode (Ohms). First, find the common wire: measure the resistance between all pairs of contacts. The pair with the least resistance is the working and starting windings combined, and the third, remaining wire is common contact. Next, by measuring the resistance between the common wire and the other two, you will determine their purpose: the resistance of the starting winding is always higher than the working winding.
Typical resistance values for household compressors with a power of 100-200 W look like this:
| Winding type | Resistance (Ohm) | Characteristics |
|---|---|---|
| Operating (Run) | 10 - 25 Ohm | Largest wire cross-section, lower resistance |
| Start | 20 - 40 Ohm | Smaller cross-section, more turns, higher resistance |
| Common | Sum of R and S | The connection point of the windings inside the engine |
If the multimeter shows one (infinity) between any contacts, then there is a break in the winding, and the compressor must be replaced. If the resistance is close to zero, an interturn short circuit has occurred. In both cases, starting directly does not make sense, the engine is faulty.
What to do if the contacts are oxidized?
If green deposits or rust are visible on the contacts, carefully clean them with fine sandpaper or a file until they have a metallic shine. Oxides create additional resistance, which can lead to false multimeter readings and poor contact when starting.
Connection diagram without a starting relay
There are two main ways to start a motor bypassing the standard relay. The first is to force the starting winding to turn on with a button or manually, the second is to use an external starting device. Let's consider a classic circuit, where we need to supply 220V to the common wire and the working winding, and apply an impulse to the starting winding only at the moment of start.
Algorithm of actions for starting using a button:
- 🔘 Connect one network wire to the common contact of the compressor.
- 🔘 Pass the second wire of the network through the button to the working winding (the engine will begin to hum, but will not start).
- 🔘 Pass the third wire (from the same phase as the button) through the button or with a short touch to the starting winding.
- 🔘 As soon as the engine starts (appears characteristic sound of operation), the starting winding circuit must be broken immediately.
This method is extremely risky, as it requires coordination and speed. If you keep the starting winding energized for more than 3 seconds, it will burn out. A safer option is to use a latching button or a toggle switch that turns off the starting winding immediately after a set of revolutions. On time the starting phase should not exceed 1-2 seconds.
⚠️ Attention: If after connecting the motor hums, but the shaft does not spin, and after 5-10 seconds the hum becomes louder, immediately turn off the power. This is a sign of a jammed mechanism or a faulty starting winding. Repeated attempts can finish off the unit.
☑️ Check before starting
Using a universal starting relay
The most civilized and safe way to check the compressor is to use a universal starting relay (for example, series PTC or electromagnetic). Such devices are sold in spare parts stores and are inexpensive. They automatically perform the function of opening the starting winding after the engine starts, simulating the operation of the standard system.
Universal relays often have color coding or a diagram on the case, which simplifies the connection. You simply need to connect the relay contacts to the corresponding compressor terminals (C, R, S) and apply power to the relay input terminal. If the relay is working properly and selected correctly, the engine will start automatically. This eliminates the human factor and the risk of overexerting the starting winding.
When choosing a relay, pay attention to the motor power indicated on the refrigerator nameplate (for example, 1/5 HP, 1/4 HP). If you install a relay designed for less power, it may not break the circuit or burn out. If it is large, the engine may not start the first time. Thermal protection, built into some types of relays, will also add safety during testing.
Diagnosis of faults during startup
Successful startup of the rotor is only half the battle. It is necessary to analyze exactly how the unit behaves. If the compressor starts, listen to the nature of the sound. A uniform hum without clanging or knocking indicates the mechanical health of the pump group. However, the absence of cold when the engine is running indicates other problems, for example, a freon leak or a blockage in the capillary tube.
Frequent symptoms and their causes:
- 🔥 The engine hums and heats up, but does not spin - jamming of the piston group or breakdown of the windings.
- ⚡ The machine knocks out or the fuse blows - a short circuit in the windings or a breakdown to the housing.
- 🌀 The engine starts, but the output pressure is weak - wear of the piston rings or valves.
- 🔊 Strong vibration and rumble - destruction of the internal suspension compressor (spring).
It is also important to check the current consumption using a current clamp. The rated current is usually indicated on the nameplate (for example, 0.8A - 1.2A). If the current is significantly higher than the nominal value, this indicates an interturn short circuit or mechanical friction. If the current is too low, the compressor may be running “idle” due to a lack of freon or a leak in the system.
Frequent errors and limitations of the method
Many technicians make the mistake of trying to start modern inverter compressors directly. Such motors (often labeled as BLDC or have three windings with the same resistance) are controlled by a frequency converter. Applying 220V directly to them will instantly burn out the electronics or windings. To diagnose them, a special tester or replacement of the control unit is required.
Another common mistake is ignoring the rest time. The compressor must not be started immediately after stopping. The refrigerant pressure in the system must equalize, otherwise the engine will not be able to overcome the back pressure and will go into protection or burn out. The minimum pause time between starts should be 5-10 minutes.
It is also worth remembering that starting “in air” (without connecting to the pipeline system) is only permissible for a short-term performance test. Long-term operation without load and without cooling by the housing can lead to overheating of the oil and loss of its properties. Vacuuming and refueling the system requires professional equipment and is not carried out as part of simply starting the engine.
Is it possible to leave the compressor connected forever without a relay?
No, you can’t. The starting winding is not designed for long-term operation. If you leave it connected, it will overheat and burn out in a few minutes or even seconds. For continuous operation, you need a standard or universal starting relay, which will turn off the starting winding after gaining speed.
Why does the compressor hum, but does not start even with a direct connection?
Most likely, the piston group is jammed due to oil burnout or moisture entering the system. In rare cases, the “wedging” method helps by applying increased voltage (through a transformer) or mechanical action, but this is a temporary measure. Most often, such a unit requires replacement.
Is it dangerous to run a compressor indoors?
Yes, it can be dangerous. Firstly, there is a risk of electric shock. Secondly, if the system depressurizes (if you sawed off the pipes), refrigerant could escape into the atmosphere. Although modern freons are not toxic in small quantities, they displace oxygen. In addition, when the windings burn, caustic smoke is released. You need to work in a ventilated place.