Using used equipment to create new useful devices is not just a way to save money, but also an excellent practice for understanding the principles of mechanics. Vacuum pumpmade from an old refrigeration unit, it becomes an indispensable assistant in the garage or home workshop. It is capable of pumping air out of air conditioning systems, helping to bleed car brakes, or being used for vacuuming products and materials during repairs.
The main value of such a solution lies in the availability of components. An old refrigerator that has long stopped freezing is often thrown away, not suspecting that its compressor can still work for decades. Unlike cheap Chinese analogues, hand-assembled units have a high service life and maintainability. heart - the compressor can still work for decades. Unlike cheap Chinese analogues, hand-assembled units have a high service life and maintainability.
In this article we will analyze in detail the process of converting a household compressor into a full-fledged tool for pumping air. You will learn what materials are required, how to properly prepare the device and what operating nuances must be taken into account for a long service life of the homemade product.
Operating principle and choice of compressor
Before starting assembly, it is important to understand exactly how it works hermetic compressor. In normal operation, it forces refrigerant at high pressure into the condenser. However, the design of the piston group allows it to operate effectively in vacuum mode, that is, to pump out air from a closed volume. The efficiency of such a pump is quite high for household tasks.
Almost any compressors from Soviet and post-Soviet refrigerators are suitable for creating a vacuum pump. Series models FK, K or more modern ones DH have proven themselves to be reliable units. The main requirement is the serviceability of the electrical part and the absence of mechanical damage to the housing.
⚠️ Attention: Never try to open the sealed compressor housing with a grinder or a hacksaw. Inside there is an inert gas and a special oil under pressure. Violation of the tightness without proper preparation can lead to splashing of oil or ignition of vapors.
When choosing a donor, pay attention to the type of launch. There are models with and without a starting capacitor. For a homemade pump, this is not critical, since the starting relay is usually retained from the original circuit. It is only important to make sure that the motor shaft is not jammed and the compressor emits a characteristic hum when turned on for a short time.
Necessary tools and materials
Assembling a vacuum pump does not require complex industrial equipment, but having a high-quality tool will significantly simplify the process and increase the safety of the work. The basis of the design will be the compressor itself, but to transform it into a pump, a number of additional elements will be required.
First of all, it is necessary to prepare a filtration system. Since a household compressor is not designed to work with atmospheric air containing dust and moisture, a filter must be installed at the inlet. You will also need an outlet filter to capture suspended oil, which will inevitably be present in the exhaust flow.
Tubes will be needed for installation. Copper tubes from the refrigerator itself can be used, but to connect the hoses it is better to purchase PVC or siline hoses of a suitable diameter. The connection of metal and flexible parts is carried out through clamps or fittings.
- 🔧 Tool set: pliers, wire cutters, screwdrivers, wrenches.
- 🛢️ Oil: special vacuum or motor (depending on the selected modification).
- 🔌 Electrics: wire with plug, possibly a new start relay if the old one is faulty.
- 🧱 Basis: plywood board or metal sheet for mounting the unit.
Special attention should be paid to the oil container if you plan to make a system with oil lubrication, although in the basic version you can get by with the standard volume. All materials must be resistant to oils and not be destroyed by vacuum.
☑️ Preparation for assembly
Preparing the compressor for rework
The first stage of work is dismantling the compressor from the refrigeration room frames It is usually mounted on four shock-absorbing bushings. Carefully unscrew the bolts and remove the unit. On the case you will see three terminals of the electrical contact group and two copper pipes (input and output).
The next step is to determine the direction of the flows. In the factory version, one pipe sucks in freon, the other pumps it out. For the pump to work effectively, you need to connect the air intake hose to the pipe that was in the refrigerator input (usually it is thinner, but not always). You can check this by applying a short-term current pulse and placing your finger near the holes: where it sucks, there is an entrance.
An important point is to change the oil. Factory refrigeration oil is hygroscopic, that is, it actively absorbs moisture from the air. When operating in vacuum pump mode, this will lead to rapid corrosion of internal parts and a decrease in performance. The oil must be drained by turning the compressor upside down and filled with new one.
⚠️ Attention: Before adding new oil, make sure that the old one is completely removed. Mixing different types of oils (mineral and synthetic) can lead to the formation of sediment and jamming of the piston group.
Some technicians recommend washing the inside of the compressor with a special solution or kerosene if there is a suspicion of the presence of freon breakdown products or acids. However, for domestic needs, it is often enough to simply replace the lubricant with a more heat-resistant analogue.
Which oil is best to fill in?
The optimal solution is the use of semi-synthetic motor oils with a viscosity of 10W-40. They are less hygroscopic than standard refrigeration oils and better lubricate rubbing pairs when working with air. You can also use specialized vacuum oils, but they are more expensive and harder to find in retail.
Assembling a vacuum installation
The assembly process begins with installing the compressor on a prepared base. There will be significant vibration during operation, so use rubber pads between the compressor feet and the plywood platform. This will reduce noise and prevent the device from “sliding” along the workshop floor.
Next comes the installation of filters. A fine fuel filter or an air filter from a car/motorcycle is installed on the inlet pipe (suction). This will protect the insides from dust. It is also advisable to install an oil separator filter on the outlet pipe, especially if you plan to use a pump for oil-sensitive systems.
The connection of the pipes to the hoses is made using adapters. The copper ends of standard tubes can be carefully flared or ready-made fittings can be used. It is important to ensure the tightness of the connections, since any air leaks at the inlet will sharply reduce the efficiency of vacuuming.
The electrical circuit remains standard. The starting relay and capacitor (if any) are connected according to the markings on the relay body. Usually the diagram is printed on the relay itself or is available on the Internet for the compressor model. Do not forget to ground the device body for safety.
The final touch is installing a pressure gauge. Although the pump is already running, visual monitoring of the vacuum helps to understand when the limit of the installation's capabilities has been reached. The pressure gauge is installed on the line between the pump and the object being evacuated.
Modernization and improvement of characteristics
The basic version of the pump is functional, but it can be significantly improved. One of the main limitations of a household compressor is heat. During prolonged operation in vacuum mode, the housing temperature can reach critical values. Installing a simple computer cooler or cooling fins will extend the life of the device.
The second important aspect is cleaning the exhaust air. Compressors are lubricated with oil, some of which is carried away as mist. If you use a pump to vacuum molds or containers, oil may get into the product. Installing an additional oil separator (for example, filled with metal shavings or padding polyester) solves this problem.
To increase productivity, you can connect two compressors in parallel. This will double the volume of air pumped out, although it will require more powerful electrical wiring and a reinforced frame. This combination allows you to quickly achieve the desired vacuum in large volumes.
| Parameter | Basic model | Upgraded version | Double unit |
|---|---|---|---|
| Residual pressure | 0.05 - 0.08 bar | 0.03 - 0.05 bar | 0.03 - 0.05 bar |
| Performance | ~100 l/min | ~120 l/min | ~200 l/min |
| Noise level | High | Medium (with muffler) | Very high |
| Complexity | Low | Medium | High |
It is also worth thinking about mobility. Installing wheels on the frame and carrying handles will make using the pump much more comfortable, especially if you plan to use it to bleed the car's brakes in different places.
Safety and maintenance
Operation of homemade equipment requires strict adherence to safety measures. The compressor operates from a 220V network, so all electrical connections must be reliably isolated. The use of a differential circuit breaker (RCD) in the power circuit is a mandatory requirement.
When working with a vacuum, there is a risk of containers collapsing. Never use glass bottles, jars, or thin-walled plastic canisters that are not designed to hold a vacuum for experiments. This may result in injury from shrapnel.
Regular maintenance will extend the life of the pump. Check the oil level and condition periodically. If it turns black or has an emulsion (water) in it, it must be replaced. You should also clean or replace the inlet filters so as not to create unnecessary resistance at the inlet.
⚠️ Attention: Do not allow the compressor to operate “dry” without oil or with a critically low level of oil. This will lead to instant overheating and scuffing of the piston group, after which restoration will be impossible.
The unit should be stored in a dry room. Moisture is the main enemy of internal metal parts, especially if non-specialized oil was used. Before long-term storage, it is useful to blow the system with dry air.
Frequently asked questions (FAQ)
What residual pressure can such a pump create?
A single-stage compressor from a refrigerator usually achieves a residual pressure in the range of 0.03–0.05 bar (absolute). For most household tasks this is sufficient, but for a deep vacuum (as in scientific laboratories) a two-stage system or a different type of pump will be required.
Can this pump be used for air conditioners?
Yes, this pump is great for vacuuming the circuits of household air conditioners and refrigerators before charging with freon. However, before use, make sure that there are no residual old oil and moisture in the system that could get into your homemade unit.
Why does the compressor get very hot?
Heating to 80-90 degrees Celsius is normal for such compressors. They are designed to operate in a mode where the refrigerant gas cools the engine. When working with air, cooling is worse. If the temperature exceeds 100-110 degrees, take a break or install a fan.
Is it necessary to change the oil immediately after assembly?
It is advisable. Factory oil may contain acidity from working with freon and moisture. Replacing with fresh, less hygroscopic oil (for example, 10W-40) will significantly increase the resource of the unit when working with atmospheric air.