Using old household equipment for new tasks is a great way to save money and extend the life of equipment. Home craftsmen often wonder how to connect a compressor from a refrigerator without a condenser in order to assemble a compact unit for aerating an aquarium, purging electronics, or inflating tires. The main difficulty here lies not in starting the engine itself, but in organizing the correct cooling and pressure relief system, the role of which in normal mode is performed by the capacitor.
The absence of a heat exchanger (condenser) radically changes the thermodynamic cycle of the device. In a standard refrigerator, freon, compressed by a piston group, enters the coil, where it gives off heat to the environment and turns into a liquid state. Without this stage the temperature at the compressor outlet can reach critical values, which can melt plastic tubes or damage valves. Therefore, before starting work, you must clearly understand that you are not creating a refrigerator, but a compressor unit with completely different operating parameters.
Nevertheless, the problem is completely solvable if certain technical conditions are met. You will need to not only correctly assemble the electrical startup circuit, but also provide alternative ways to remove heat and stabilize pressure. In this article we will analyze in detail the physical principles of the system, the necessary components for safe assembly and a step-by-step connection algorithm. Attention to detail at the planning stage will protect you from breaking expensive equipment and ensure a long service life of your homemade product.
Fundamental differences in working without a heat exchanger
To understand how to start a unit under new conditions, you need to understand the physics of the process. In normal mode condenser serves as a buffer that equalizes pressure and temperature. When you remove it from the circuit, you are essentially connecting the discharge pipe directly to the atmosphere or low volume receiver. This leads to the fact that the hot air does not have time to cool down and immediately goes further through the system.
The key parameter becomes discharge temperature. Without a long coil to dissipate heat, it grows exponentially. If in a refrigerator the compressor works in tandem with an evaporator, which cools the return gas, then in the mode of a supercharger into the atmosphere or a cylinder this effect is absent. The oil used to lubricate the rubbing parts may begin to burn, forming carbon deposits on the valves, which will reduce performance over time.
⚠️ Attention: Operating the compressor without an effective heat sink for more than 15-20 minutes at a time can lead to thermal deformation of the valve plate and piston jamming.
In addition, the nature of the load on the electric motor changes. In the absence of resistance of the condenser and capillary tube, it is easier for the motor to crank the shaft at the start, but as pressure builds up in the receiver, the load grows differently than in a closed refrigerant circuit. It is important to consider that starting current remains high, and the protection system must work correctly to avoid overheating of the windings.
Necessary components and tools for assembly
Before proceeding with installation, it is necessary to prepare all elements of the future installation. Working with electricity and pressure requires reliability, so the use of quality materials is strictly necessary. You will need not only the compressor itself, but also a number of additional components that will take on the functions of a remote condenser.
Here is the basic list of what should be at hand:
- 🛠️ Itself compressor from the refrigerator (preferably in working order, with intact tubes).
- ⚡ Starting and protective relay (standard or universal, selected for the engine power).
- 🔋 Receiver (compressed air container) with a volume of 5 to 50 liters, capable of withstanding pressure up to 10 atmospheres.
- 🌡️ A check valve that prevents the reverse flow of air into the compressor when stopped.
- 🔌 Electrical cable with a plug, a switch and, preferably, a circuit breaker.
Special attention should be paid oil separator. Since the refrigerator compressor is oil-based, some of the lubricant will fly away in the form of mist along with the air. For tasks where clean air is important (for example, aerography), installing an oil separator filter is critical. You will also need copper or brass fittings, high-pressure hoses and clamps.
The tools you will need are: wire cutters, pliers, screwdrivers, a multimeter to check the windings and, possibly, a soldering iron to connect the contacts. Don't forget about sealant for threaded connections, for example FUM tape or anaerobic sealant to prevent air leaks.
Electrical connection diagram and starting the engine
The most critical stage is electrical connection. Refrigerator compressors are usually equipped with an asynchronous motor, which requires a phase shift to start. This task is performed by the starting winding, which is switched on only for a short time. This process is monitored by a special relay.
The standard connection diagram is as follows: three contacts are suitable for the compressor. Two of them are the working and starting stator windings, and the third is the common wire. A time relay or starting relay with a thermal contact automatically turns off the starting winding after the rotor accelerates. If you are using a native relay, simply follow the markings or diagram on its body.
Contact connection diagram:1. Common (Common) - connects to one pole of the network.
2. Working winding (Run) - connected via a protective relay.
3. Start winding (Start) - connected through a starting device.
If the original relay is lost or faulty, it can be replaced with a universal one or use a capacitor starting circuit, selecting the capacitance experimentally. However, for beginners it is safer to use the original relay, since it is already matched to the characteristics of the motor. Phasing in a single-phase network it is not important, but grounding the compressor housing is strictly necessary for safety.
☑️ Check before the first start
Organization of the cooling system and receiver
Since we are removing the condenser, the function of primary cooling and flow stabilization should be taken over by the receiver. This is a metal cylinder that dampens pressure pulsations and gives the air time to cool a little before being released to the consumer. Without a receiver, using a compressor without a condenser is almost impossible due to pulsations and overheating.
The receiver can be made from an old fire extinguisher or a gas cylinder that has previously been hydrotested. It is important that the capacity of the container is sufficient for your compressor. A receiver that is too small will cause the motor to start frequently, and a receiver that is too large will take a long time to fill. The optimal ratio is considered to be 10-20 liters of volume for every 100 W of motor power.
⚠️ Attention: When using homemade receivers, be sure to install a safety valve set to a pressure below the strength limit of the cylinder. An explosion of a container under pressure is deadly!
To improve cooling, you can add a piece of copper tube, rolled into a spiral and not insulated, to the outlet pipe of the compressor. This will create the effect of an air radiator. It is also useful to place the receiver itself in a place with good ventilation. Temperature conditions is the main enemy of the durability of your assembly.
Can I use plastic containers?
Use plastic bottles or canisters as receiver is STRICTLY PROHIBITED. The plastic does not hold pressure and bursts when heated, turning into fragments. Metal only!
Technical characteristics and compatibility table
When assembling a compressor unit, it is important to take into account the parameters of a specific engine. Different models of refrigeration compressors have different capacities and permissible operating pressures. The use of unsuitable components can lead to rapid failure.
Below is a table with approximate characteristics of popular types of compressors that are often used for refurbishment:
| Compressor type | Power, W | Performance, l/min | Max. pressure, atm | Features |
|---|---|---|---|---|
| Low temperature (R134a) | 100-120 | 30-40 | up to 6 | Requires synthetic oil |
| Medium temperature (R600a) | 80-100 | 25-35 | up to 5 | Explosive refrigerant (ventilation required) |
| Powerful (from large refrigerators) | 150-200 | 50-70 | up to 8 | High levels of noise and vibration |
| Compact (mini-refrigerators) | 50-70 | 15-20 | up to 4 | Low performance, quiet operation |
Pay attention to the type of refrigerant which the compressor is rated for even if you don't use freon. Compressors under R600a (isobutane) require special care when sawing the housing, as flammable gas may remain inside. It is better to blow them with air before any manipulation with metal. It is also important to remember about the type of oil: mineral or synthetic, since they are not always compatible.
Typical errors and safety measures
Assembling a compressor with your own hands is associated with risks that should not be forgotten. The most common mistake is ignoring the heating of the outlet pipe. Many beginners use conventional PVC hoses, which soften at temperatures of 100-120°C and can burst under pressure. Use only heat-resistant materials: copper, brass, special hoses for pneumatics.
Another mistake is the lack of filtration at the inlet. The atmospheric air contains dust, which, when it enters the compressor cylinders, acts as an abrasive. This quickly wears out the piston group and rings. Be sure to install an air filter on the suction pipe, even if it is just a piece of foam rubber in the carburetor housing.
Electrical safety also comes first. The compressor housing must be grounded. All connections must be securely insulated. Do not allow moisture to enter the electrical part, especially if the compressor will be used outdoors or in a damp area.
Frequently asked questions (FAQ)
How long can the compressor operate without interruption?
In supercharger mode without full freon cooling, it is better to limit the time of continuous operation to 15-20 minutes. After this, a break is required to cool the case to ambient temperature. Long-term operation will lead to overheating of the oil and degradation of the seals.
Is it necessary to change the oil in the compressor during refurbishment?
If the compressor is old and the oil in it has turned black or lost its properties, it is advisable to replace it. However, to do this you need to carefully open the case, which is difficult to do hermetically at home. If the compressor runs quietly and does not overheat, you can leave the standard oil.
Can such a compressor be used for painting?
Yes, you can, but only if you install a high-quality moisture-oil separator. The escaping air will contain microparticles of oil that will damage the coating. For airbrushing, this is critical, so the filtration system must be multi-stage.
Why does the compressor hum, but does not start?
Most likely, the problem is in the start relay or the start winding. The cause may also be a jammed piston due to long periods of inactivity. Try gently tapping the housing or applying a short-term voltage pulse, but it is better to check the resistance of the windings with a multimeter.
What is the maximum pressure you can get?
Refrigeration compressors are not designed to create high pressure. Usually they confidently pump up to 6-8 atmospheres. Trying to inflate more may lead to destruction of the seals or gaskets. For pressures above 10 atmospheres, specialized compressors are needed.