Compressor from the old one The household refrigerator is a valuable resource for DIYers that often gets a second life in garages and workshops. Powerful sealed electric motor is great for creating homemade compressors for airbrushing, tire inflation or pneumatic tools. However, by simply removing the unit from the case, you will not be able to start it directly, since the factory connection diagram was tied to the thermostat and the protection system, which remained on the old frame.
For a successful start, you need to understand the electrical part, find the terminals of the starting and working windings, and also choose the right starting device. Errors in this process can lead to overheating of the windings, failure of the capacitor, or even a short circuit in the network. In this article, we will analyze in detail the process of identifying contacts, connection diagrams via the starting relay, and safety measures when working with high voltage.
Before you begin manipulating the wires, you need to ensure the integrity of the unit itself. If the compressor has been removed from a non-working refrigerator, the first thing you should check is whether it has been “broken” into the housing and whether the system’s tightness has been preserved. Proper preparation and diagnostics will save you time and protect you from electric shock during further operation of your homemade device.
Identifying the type of compressor and diagnostics
The first step in the connection process is identifying the type of your compressor. Most household refrigerators are equipped with piston sealed units, which are divided into low-temperature and medium-temperature. Not only productivity, but also the requirements for starting equipment depend on this. Modern models often use inverter motors, the connection of which requires complex electronics, so for homemade products they usually choose classic options with a starting relay.
Visual inspection of the housing will help identify the presence of damage, traces of oil or rust, which may indicate depressurization. If traces of active corrosion or mechanical dents are visible on the pipes, there is no point in starting such a motor - it will either not create pressure or will quickly fail. Also pay attention to the marking of the nameplate: it indicates the supply voltage, type of refrigerant and power consumption, which is critical for selecting circuit components.
⚠️ Attention: Never connect the compressor if air or gas under pressure does not come out of its connections when unscrewing. This may indicate the presence of a vacuum or residual freon, which requires special disposal measures.
Diagnostics of the electrical part begins with checking the resistance of the windings. To do this, you will need a multimeter switched to resistance (Ohms) measurement mode. It is necessary to “ring” all three contacts on the motor block relative to the housing: if the device shows a resistance close to zero or, conversely, a break (one in the most significant digit), then the motor is faulty. The normal resistance of the working winding is usually 10-15 Ohms, and the starting winding is 20-35 Ohms, although the values may vary depending on the model Danfoss or Atlant.
Searching and marking contact terminals
On the top of the compressor there is a contact group, closed with a plastic cover, where there are three output. These contacts correspond to the working winding, the starting winding and the common wire. It is not difficult to find them: they form a triangle, and the master’s task is to correctly identify each of them, since mixing up the wires can burn the starting relay or the motor winding itself when starting.
Identification is done by measuring the resistance between pairs of contacts. You need to measure the resistance between each two of the three contacts. the least resistance is the working and starting windings combined, but we need to find the common wire. The logic is simple: the sum of the resistances from the common wire to the other two should give the resistance between these two others. In practice, we are looking for a contact whose resistance to the other two will be the greatest in total.
For clarity, let's look at the typical values that you can get from measurements on a working engine:
| Pair of contacts | Expected resistance | Description |
|---|---|---|
| Common - Working | 10-15 Ohm | Working winding (thicker wire) |
| Common - Starting | 20-35 Ohm | Starting winding (thinner wire) |
| Working - Starting | The sum of the two is higher | Serial connection |
After you have identified the common wire (often it is marked with the letter C or Common), the working winding (R or Run) and the starting winding (S or Start), it is recommended to immediately sign them with a marker or stick colored labels. This will eliminate confusion when assembling the final circuit. Remember that the colors of the wires inside the relay may not match the standards, so you need to rely on measurements with a multimeter, and not on the color of the insulation.
Selecting and connecting a starting relay
The key element of the starting circuit is the starting relay. It briefly supplies voltage to the starting winding at the moment the engine starts, creating the necessary torque, and then turns it off when the motor picks up. rpm. Without this device, the engine will only hum, but will not start, which will lead to rapid overheating and combustion of the windings.
Relays come in different types: posistor (solid-state) and with an inductor (electromagnetic). position "top-bottom" and require installation strictly vertically, according to the arrow on the case, otherwise the contacts may stick or not open.
The connection process is as follows:
- 🔌 Install the relay on the compressor contacts, observing the marking
C,R,S. It should sit tightly on. terminals. - 🔌 Connect the phase wire of the network (220V) to the contact of the working winding of the relay (usually marked
LorM). - 🔌 Connect the neutral wire of the network to the contact of the common winding of the compressor (via the relay terminal).
- 🔌 Check the tightness of all connections to prevent sparking.
It is important to select a relay with the appropriate power range (indicated on the body, for example, 1/4 HP or 1/5 HP). If the relay power is too low for your engine, the contacts inside may weld and the starting winding will not work. If it is too high, the engine may not start the first time.
What to do if the relay clicks, but the motor does not start?
If you hear a characteristic click, but there is no rotation, the piston group may have jammed or the starting winding has burned out. Try to carefully (with the power off!) turn the motor shaft through the pipe or give a short impulse. external force, but be careful.
Using a capacitor for starting
In some circuits, especially when using compressors to create excess pressure above atmospheric, one starting relay may not be enough. In such cases, a capacitor is added to the starting winding circuit, it creates a phase shift, increasing the starting torque, which allows the motor to more easily overcome the resistance of the compressed one. air.
The capacitor capacity is selected experimentally or according to tables for a specific type of engine. Typically, for household refrigeration compressors, capacitors with a capacity of 20 to 50 μF with an operating voltage of at least 250V are used (it is better to take a reserve - 350V or 450V). Exceeding the capacity can lead to overheating of the starting winding, and insufficient - to the impossibility. startup under load.
⚠️ Attention: Capacitors accumulate an electrical charge. After turning off the device, be sure to discharge the capacitor by shorting its contacts through a dielectric (for example, with a screwdriver with an insulated handle) to avoid electric shock.
The capacitor is connected in parallel with the starting winding or in series with the starting contact of the relay, depending on the selected circuit. For temporary use (only at the time of start-up), a button is often used that opens the capacitor circuit after a set of revolutions, but in automatic systems this function is taken over by a centrifugal or thermal relay. The use oil capacitors is preferable to electrolytic ones due to their ability to operate in alternating current circuits without the risk of explosion.
Assembling the electrical circuit and safety measures
Assembling the final circuit requires care and compliance with the rules electrical safety. All connections must be made in a junction box or protected enclosure. Open twisting of wires is unacceptable, especially if the compressor will be used in a garage or workshop, where there may be high humidity or dust.
A mandatory element of the circuit is a circuit breaker or fuse designed for the current consumption of the engine plus a small margin. This will protect the wiring from short circuits and fires if the compressor malfunctions. It is also highly advisable to ground the metal body of the unit, if it is not insulated, in order to prevent electric shock if the insulation of the windings breaks down on the body.
Here is a checklist for checking the assembled circuit before turning it on for the first time:
☑️ Check before starting
When starting for the first time, do not immediately connect the hose to the consumer. Let the compressor idle for a few seconds to assess the noise and vibration patterns. If the engine hums smoothly, without knocking or sudden changes in tone, and the relay clearly clicks when starting and stopping, you can proceed to testing under load.
Typical errors and troubleshooting
Even experienced professionals may encounter problems when starting old equipment. One of the most common mistakes is incorrect identification of the common wire. If you apply 220V to the starting and operating windings at the same time, bypassing the phasing, the engine will not start and will hum strongly, quickly heating up. In this case, you need to immediately turn off the power and recheck the resistance measurements.
Another common problem is sticking of the start relay contacts. This happens if the relay is selected incorrectly or is faulty. As a result, the starting winding remains energized constantly, which leads to its combustion in a matter of seconds. If you smell something burning or see smoke, turn off the power to the system immediately. It is also worth checking the condition of the oil: if the compressor has been lying on its side for a long time, the oil may have drained into the system, and water hammer may occur during startup.
Often included:
- 🔥 Overheating: The engine is hot to the touch after 2-3 minutes of operation. Reason: poor ventilation or incorrectly selected capacitor.
- 🔇 Lack of noise: The compressor hums, but does not pump. Reason: break in the suction pipe or violation of the tightness of the valves.
- ⚡ Knocking out plugs: Instant operation of the machine. Reason: short circuit in the windings or breakdown in the housing.
If the compressor makes a metallic knock, this may indicate that the internal motor suspension (springs) has burst and the “heart” is beating against the walls of the casing. Operating such a unit is dangerous and noisy; repairing it at home is almost impossible.
Frequently asked questions (FAQ)
Is it possible to connect a compressor directly without a relay?
Theoretically, you can start the engine by briefly applying voltage to the starting winding manually through a button, but it requires precise timing and is dangerous. For constant operation, the relay is necessary, since it automatically turns off the starting winding. Operation without disconnecting the starting winding will lead to its combustion.
What kind of oil should be poured into the compressor from the refrigerator?
In hermetic compressors, oil is not added during operation, since the system is closed. If replacement is required (after repair), special synthetic or mineral oil for refrigeration compressors is used (for example, Frigate or Mobil), depending on the type of refrigerant with which the unit worked. Regular motor oil cannot be used.
Why does the compressor hum but does not start?
Most often this indicates a malfunction of the starting relay (contacts are stuck or the coil is burned out) or the capacitor. The cause may also be jamming of the piston group due to exhaustion or lack of oil. Try replacing the relay - this is the cheapest and most common option for a breakdown.
Is it possible to use a compressor from a refrigerator to paint a car?
Yes, you can, but with restrictions. Refrigeration compressors are not designed to operate under high pressure for long periods of time and do not have efficient air cooling. They overheat quickly. They are great for airbrushing or inflating tires, but a spray gun will require a large receiver and mandatory pauses in operation to cool down.