The situation when the refrigerator stops cooling, but there is silence inside or, conversely, a hum is heard, but there is no cold, often indicates a malfunction of the start-up protection equipment. Owners of household appliances often wonder whether it is possible to revive the unit on their own by replacing a burnt-out part or starting the engine directly to check. Compressor is the heart of the system, and its performance directly depends on the correct supply of voltage to the windings at the right time. To understand the process, it is necessary to clearly understand how the electrical network start relay and the windings of the electric motor interact.
Before taking up tools, it is important to realize that working with electricity and refrigerants requires caution. In this article we will analyze the theoretical and practical aspects of connection that will help diagnose a breakdown or temporarily start the system. However, it is worth remembering that video instructions on the Internet they often show ideal conditions, while in reality you may encounter oxidized contacts, burnt wiring or specific features of your refrigerator model.
The main purpose of this article is to give you a structured understanding of the electrical circuit and the algorithm of actions. We will look at relay types, multimeter diagnostic methods, and circuit assembly procedures. A correct understanding of how it works capacitor motor and its starting circuit will save you from costly mistakes, such as burning windings when the phasing or voltage is connected incorrectly.
Design and principle of operation of the compressor
Sealed piston compressor, which is installed in most household refrigerators, is a complex electromechanical unit. Inside the steel casing there is an electric motor and a compressor part, united by a common shaft. To start the engine, it is necessary to create torque, since single-phase current by itself cannot turn the rotor from rest. This is exactly what starting relayserves, which briefly connects the starting winding.
The electrical circuit of the engine contains two main windings: the working (main) and the starting. The working winding has a larger wire cross-section and lower resistance; it is designed for continuous operation. The starting winding is made of thinner wire, has a high resistance and is turned on only at the moment of start in order to create the necessary phase shift. If you forget to turn off the starting winding, it will burn out in a matter of seconds due to overheating.
⚠️ Attention: Prolonged supply of voltage to the starting winding without a working centrifugal relay mechanism is guaranteed to lead to an interturn short circuit and engine failure.
Thermal relay, which is often structurally combined with the starting one or located nearby, serves to protect against overloads. Inside it there is a bimetallic plate that bends when heated and opens the circuit if the current exceeds the rated values. This protects stator windings from burnout when the piston group jams or power surges.
Types of starting relays and their markings
In household refrigeration equipment, two main types of starting devices are used: induction (electromagnetic) and posistor. Induction relay works on the principle of an electromagnet: when voltage is applied, current passes through the coil, creating a magnetic field that draws in the core and closes the contacts of the starting winding. As soon as the rotor picks up speed, the current drops, the core drops, and the circuit opens. Such devices are often marked P-1, P-2, P-3 and are installed vertically, strictly in the direction of the arrow.
Posistor relays, or starters with thermistor, are more modern and reliable. Inside the case there is a ceramic element (posistor), which at room temperature has low resistance and passes current to the starting winding. Under the influence of current, it heats up, its resistance increases sharply, and the current practically stops flowing, effectively breaking the circuit. To restart such a relay, it takes time to cool down (usually 2-5 minutes), which explains the pauses when trying to turn it on frequently.
When replacing or checking, it is important to pay attention not only to the type, but also to the electrical characteristics. Each relay housing is marked with a marking indicating the permissible engine power and the type of refrigerant. Using a relay with inappropriate parameters, for example, installing a device for R134a on a system with R600a, can lead to incorrect operation or startup failure.
How to distinguish an inductive relay from a posistor relay?
An inductive relay makes a noise when shaken a characteristic knock (the running core dangles inside), while the posistor is monolithic and does not make noise. In addition, induction relays often have a lever or arrow indicating the need for vertical installation, while posistor relays are less critical to orientation, although it is also preferable to install them according to the diagram.
Diagnostics and testing of windings with a multimeter
Before assembling the circuit, you need to make sure that the electric motor itself is in good condition. To do this, you will need multimeterconfigured to measure resistance (200 Ohm or 2 kOhm mode). First remove the start and thermal relays, as well as the capacitor (if equipped) to gain access to the three contacts on the compressor. These contacts form a triangle and correspond to the terminals of the windings.
Ring the pairs of contacts with each other. You need to find three resistance values. The sum of the two smaller resistances should be equal to the largest resistance (the resistance between the working and starting windings). Typically, the resistance of the working winding is 10-20 Ohms, the starting winding is 30-50 Ohms, and the total is the sum of these values. If the multimeter shows one (infinity) or zero, it means there is a break or short circuit in the windings.
It is also necessary to check the absence breakdown to the housing. Switch the multimeter to dial mode (with sound) or high resistance measurement mode. Press one probe against 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 not make a sound, and the arrow or numbers should not change. The appearance of resistance indicates that the engine is “broken” and it is dangerous to operate it.
| Pair of contacts | Expected resistance | Possible malfunction |
|---|---|---|
| Working - Starting | Sum of the other two | Norm (if converges) |
| Working - General | 10 - 25 Ohm | Open or short circuit |
| Starting - General | 20 - 50 Ohm | Open or short circuit |
| Any - Housing | Infinity (∞) | Insulation breakdown |
If the values differ greatly from the standard ones, but there is no breakdown to the housing, the motor may be in good order, but have an interturn short circuit. In this case, when starting up, it will hum strongly, overheat and knock out the thermal protection. In this case, an accurate diagnosis can only be made by a master using an interturn short circuit tester.
Connection diagram and circuit assembly
To connect the compressor outside the refrigerator (for example, for testing or use as a compressor for an airbrush), you will need to assemble a simple circuit. It consists of a power cord with a plug, a start relay, a thermal relay (optional, but desirable) and the compressor itself. It is important to strictly follow the sequence: phase and zero come to the input of the thermal relay, then to the working winding, and the starting winding is connected through the starting device in parallel.
☑️ Check before the first start
The contacts on the compressor are often not labeled, so they need to be determined by the resistance that you measured earlier. The common contact (Common) is located between the working and starting windings and has the least resistance in relation to both of them (or is the point from which the other two measurements come). The working winding (Run) has less resistance relative to the total than the starting winding (Start). It is this logic that is based on electrical diagram connections.
When installing the relay, it is important to correctly orient it to the compressor terminals. Induction relays have an arrow that should point up (away from the compressor). The posistor relays are simply put on all the way, but it is important that they sit tightly on the contacts and do not dangle. If you use an external capacitor (in some older circuits or for powerful motors), it is connected in parallel with the starting winding.
⚠️ Attention: Do not connect the compressor to the network without a fixed starting relay. Trying to start the engine by simply closing the contacts with a screwdriver is extremely dangerous and can lead to electric shock or fire.
For ease of assembly, you can use a terminal block or twists carefully insulated with heat shrink or electrical tape. However, remember that any connection must withstand inrush currents that are 5-7 times the operating current of the motor. The use of thin wires or poor contact will lead to heating and melting of the insulation.
Launch and test operation
After assembling the circuit, you can begin a test run. Plug the plug into the outlet. If everything is assembled correctly, you will hear a confident hum of the running motor and feel the flow of air or freon (if a hose is connected) at the outlet. The engine should run smoothly, without strong vibration and extraneous metallic knocks. After some time (depending on the type of relay), the starting device should click, turning off the starting winding.
Pay attention to the current consumption. If you have a clamp meter, check the amperage. It should not exceed the nominal values indicated on the compressor nameplate (usually 0.5 - 1.5 Amperes for household models). Excess current indicates problems in the mechanical part or windings. If the motor hums but does not spin, and after a few seconds the thermal relay clicks, it means that the starting device is not performing its function or the compressor is jammed.
If the compressor is used for technical needs (not for a refrigerator), it is important to organize heat removal. Household refrigeration compressors are cooled by gas (freon), which circulates through the system and carries away heat from the windings. When operating “in air” or in a closed circuit without a heat exchanger case temperature it can reach critical values, which will lead to protection activation or destruction of insulation.
Frequent errors and safety measures
One of the most common mistakes is ignoring grounding. In the event of an insulation breakdown, the metal housing of the compressor may be exposed to a voltage of 220 Volts. If you are conducting experiments in a garage or workshop, be sure to use RCD (residual current device) or at least ground the housing to a metal structure that goes into the ground.
Another mistake is incorrect orientation of the compressor during operation. In domestic refrigerators, the compressor is suspended on springs inside the casing, and the oil in it is distributed taking into account this position. If the compressor is turned over or placed on its side, oil may flow into the working chamber, which will lead to water hammer and valve failure during startup. Always try to maintain the factory position of the unit.
Also, do not forget about the pressure. Household compressors are not designed to create high pressure in the receiver without proper automation. Discharge pressure may exceed the strength characteristics of the casing or connections, resulting in explosive depressurization. Be sure to install pressure reducer a safety valve if you use the motor for compressor tasks.
⚠️ Attention: The air (or gas) leaving the compressor may contain oil vapors and have a high temperature. Do not direct the jet at people, flammable objects or sensitive surfaces.
When working with refrigerants (if you are restoring a refrigerator), remember that old freons (R12, R22) can be fire hazardous or toxic if in contact with an open flame. New freons (R600a - isobutane) are a flammable gas, so any work on soldering tubes should be carried out only after complete evacuation of the system and purging with nitrogen.
Possible problems and their solutions
Even with proper assembly, nuances may arise. If the compressor runs but gets very hot, check the ventilation and cleanliness of the condenser (if equipped). If the motor hums and does not start, try manually (shortly!) applying an impulse to the starting winding through the button - if it starts, then the problem is in the starting relay. If this does not help, the mechanics may have jammed.
Frequent tripping of the thermal relay may indicate increased current consumption. This happens when the network voltage is low or when using a relay that is not suitable for the power of the given motor. Check the voltage in the socket and the compliance of the compressor power relay markings.
What to do if the winding burns out?
Restoring a burnt winding in a hermetic compressor at home is impossible. Rewinding of the stator is required, which is not economically feasible. The only way out is to replace the compressor with a new one or a used one in good condition.
Is it possible to start a compressor without a relay?
Theoretically, it is possible if you manually apply voltage to the starting winding at the moment of start and remove it immediately after gaining speed. However, it is difficult to do this efficiently without special equipment. There is a risk of not having time to remove the starting winding, which will lead to its combustion. For one-time tests, a button is used, but for continuous operation a relay is necessary.
What kind of capacitor is needed for a compressor?
In most modern household refrigerators, a capacitor is not used; the phase shift function is performed by the design of the starting relay. However, older models or industrial units may use starting capacitors. Their capacity is selected strictly according to the motor passport (usually from 10 to 50 uF) with a voltage of at least 300-400 Volts.
Why does the compressor turn on for 5 seconds and turn off?
This is a classic thermal protection job. Reasons: 1) The starting relay is faulty (does not open the starting winding or does not close it at start). 2) The compressor is jammed (mechanical failure). 3) Breakdown of the windings. 4) Critically low voltage in the network.
Is it dangerous to use an old compressor for painting?
You can use an old refrigeration compressor for airbrushing, but with caution. The exhaust air will contain oil mist, which must be filtered through an oil separator, otherwise the paint will be defective. Also, such compressors are not designed for long-term operation under load and can quickly overheat.
How to determine the common wire if there is no marking?
You need to ring all three contacts together. You will get three resistance values. The contact that participates in the two smaller resistances (the sum of which gives the third, largest resistance) is common. The contact with the least resistance relative to the total is the working winding, the one with the highest is the starting winding.