Making a vacuum pump from a refrigerator compressor with your own hands

Converting an old refrigeration unit into a functional tool is a classic example how home craftsmen give a second life to old equipment. Refrigerator compressor by its design, it is a ready-made piston mechanism capable of creating a vacuum, which makes it an ideal basis for creating a homemade vacuum pump. Such a device can be useful in the garage for vacuuming air conditioning systems, bleeding brakes, or even for conducting simple chemical experiments.

However, before you begin disassembling, you must clearly understand the operating principle and limitations of a standard household compressor. Unlike specialized industrial installations, a household unit is not designed to work with aggressive media or solvent vapors without modifications. Sealed housing hides inside an electric motor and a pump group immersed in oil, which acts as a lubricant and sealant. It is this oil that often becomes a problem during conversion, since it can be ejected along with the air flow, requiring the installation of additional oil separator filters.

The main advantage of this solution is the availability and low cost of the source material. Old refrigerators are often thrown away or sold for pennies, but their “heart” continues to work for many years in a new role. In this article we will analyze in detail the transformation process, from choosing the appropriate model to final assembly and testing of the system.

Operating principle and choice of source material

Fundamentally, any piston compressor works due to the reciprocating movement of the piston inside the cylinder. When the piston moves down, a vacuum is created in the chamber and air is sucked in through the inlet valve. When moving upward, the volume of the chamber decreases, the pressure increases, and the compressed air is pushed out through the outlet valve. Vacuum pump uses the same mechanics, but its task is to pump gas out of a closed volume, creating negative pressure there.

Almost all compressors from household refrigerators are suitable for conversion, but there are nuances. Units with an old-style starting relay (heavy, round “barrels”) are often more repairable and easier to connect than modern frequency-controlled models. It is important to pay attention to the integrity of the housing and the absence of signs of burning of the windings. If the compressor hums but does not start, the mechanics may be jammed, and it is better to put such a unit aside.

⚠️ Attention: Never try to open the welded compressor housing with a grinder or hacksaw under voltage or immediately after work. Residual freon pressure may remain inside, and oil vapor in combination with a spark from the tool may ignite. Allow the unit to cool completely and release the pressure through the process pipe.

When choosing a donor, it is also worth assessing the noise level. Modern compressors can be quieter, but their design is often more difficult to modify. Old Soviet models, such as FK-1.5 or K-50are distinguished by increased reliability and simplicity, although they are louder. Engine power usually varies from 100 to 200 Watts, which is quite enough for most garage tasks.

Necessary tools and consumables

For successful implementation of the project, you will need not only the compressor itself, but also a number of additional components that will ensure the security and functionality of the system. A basic set of tools can be found in any home craftsman's garage, but some specific parts may need to be purchased at a plumbing or auto parts store.

First of all, you need tools for working with metal and electrical work. Cutting tubes, cleaning contacts and securely fixing elements is the key to the longevity of the device. You should not skimp on fasteners and sealants, as the system will operate under vacuum, and any microcrack will reduce the efficiency of the pump to zero.

• 🛠️ A set of wrenches, screwdrivers and pliers for dismantling and assembly.
• ⚡ Soldering iron, solder and electrical tape connections.
• 🔧 Pipe cutter or hacksaw for working with copper tubes.
• 🔩 Clamps, bolts, nuts and metal strip for creating a frame.
• 🧪 High-temperature sealant or silicone for sealing connections.

Particular attention should be paid to materials for the receiver and filters. As a receiver, you can use an old fire extinguisher, a gas cylinder, or even a durable plastic canister (with vacuum restrictions). You can make your own filters from glass jars or buy ready-made car fuel filters. It is important that all materials are resistant to the effects of oil that will circulate in the system.

Preparing the compressor for rework

The first stage of work is the correct one preparation of the unit. Refrigerator compressors have three copper tubes coming out of the housing: two short and one long (usually). The short ones are for refrigerant inlet and outlet, and the long one (often sealed) is for oil charging at the factory. Our task is to determine which tube is suction and which is discharge.

To do this, it is enough to briefly supply power to the motor windings (following the connection diagram through the starting relay). The tube that will begin to actively suck in air (check with your palm) is the entrance. The tube from which air blows forcefully is the exit. It is better not to touch the third, sealed tube for now; it can serve as an inspection window for the oil level or drainage.

After identifying the pipes, it is necessary to thoroughly rinse the insides of the compressor. In old refrigerators, freon and its breakdown products may remain inside. Blowing compressed air through all holes will help remove excess chemicals. It is also recommended to change the oil if it turns black or has an acidic odor, although regular low-viscosity motor oil is often suitable for the vacuum pump.

⚠️ Attention: When working with copper tubing, use only a pipe cutter. A hacksaw will leave chips inside the tube, which will get into the compressor mechanism and can cause the piston group to jam.

Assembling the filtration system and receiver

The most critical part of the project is organization of effective oil separation. Since the compressor operates in an oil bath, the blown air will carry microscopic droplets of oil. If this air goes directly into the vacuum chamber or air conditioning system, the oil will clog all the channels and ruin the operation of the equipment. Therefore, a filtration system is required.

The receiver performs a dual function: it stabilizes the pressure (or vacuum), smoothing out pulsations from the piston, and serves as a primary settler for oil. The larger the receiver volume, the smoother the flow will be. For a vacuum pump, a container with a volume of 10-20 liters is sufficient. It is better to place the inlet and outlet holes in the receiver diagonally so that the air flow travels the maximum path.

• 🌪️ Coarse filter: installed at the inlet of the compressor to protect from dust.
• 🛢️ Oil separator: container with filler (expanded clay, shavings) or cyclone type after the compressor.
• 🔒 Check valve: prevents air from being sucked back into the system when the engine is stopped.
• 📉 Vacuum gauge: necessary to control the degree of vacuum in the system.

For the manufacture of filters, transparent plastic bottles or glass jars with two holes in the lid are often used. Inside you can place a padding polyester or a car fuel filter. This design allows you to visually monitor the degree of contamination and the amount of collected oil. Regular cleaning or replacing the filter element will extend the life of the pump.

Electrical diagram and motor connection

Connecting the compressor motor requires care, so how incorrect switching of the starting winding can lead to the motor burning out or knocking out plugs. Most household refrigerators use a motor with a starting winding and a starting relay (RTK, R-1 and analogues). The relay is necessary for short-term connection of the starting winding at the time of start.

The connection diagram is usually simple: two contacts go to the main working winding, and one contact (via a relay) to the starting winding. The relay body often has markings or a diagram on it. If the markings are erased, you can call the windings with a multimeter. The resistance of the working winding is always less than the starting winding. It is important to ensure reliable contact and insulation of all connections, since the compressor can vibrate.

Connection diagram via the RTK relay:
1. Contacts 1 and 2 of the relay -> 220V network (through a capacitor or directly, depending on the model).
2. Relay contact 3 -> Engine starting winding.
3. The working winding is constantly connected.
*It is important to observe phasing if the relay is electromechanical (vertical orientation).

For ease of operation, it is worth assembling a separate starting unit with a power button, a fuse and, preferably, a thermal protection relay. Thermal protection will save the engine from overheating during prolonged operation. It is also useful to install a toggle switch to forcibly turn off the power in an emergency.

What happens if you mix up the windings?

If you apply voltage only to the starting winding or connect the relay incorrectly, the engine will start to hum, overheat and burn out in a few minutes. The starting winding is designed for short-term operation only at the moment the rotor starts.

Testing, starting and safety measures

The first start-up of the assembled device is a crucial moment. You should not immediately connect the system to a vacuum chamber. First check the pump at idle speed. Turn on the power and listen: there should be no knocking, grinding or excessive vibration. Check the connections with a soap solution - the appearance of bubbles will indicate air leaks, which is critical for the vacuum system.

The optimal time for continuous operation of a household compressor in pump mode should not exceed 20-30 minutes. They are not designed for 24/7 operation and may overheat. If you require long-term pumping, provide breaks for cooling or organize forced cooling of the case (for example, point a fan at it).

⚠️ Attention: When creating a deep vacuum in closed containers (glass jars, thin-walled canisters), there is a risk of the container collapsing under atmospheric pressure. Use only containers designed for vacuum, or monitor the process visually.

Regularly check the oil level in the compressor through the inspection window or dipstick. When operating in pump mode, oil loss may be higher than in normal refrigerator mode. Timely topping up will prevent dry friction and rapid wear of parts.

Frequent problems and ways to solve them

During the operation of a homemade pump, typical problems associated with design features may arise. Understanding the causes of malfunctions will help you quickly restore the device’s functionality without contacting specialists.

One ​​of the common problems is a drop in performance. This may be caused by dirty filters, worn piston rings, or loss of tight connections. Also, the compressor may stop creating a vacuum if the oil level drops below a critical level and the valves no longer shut off flows normally.

• 📉 Weak vacuum: Check the tightness of all joints with a soap solution, replace the oil with a more viscous one.
• 🔥 Overheating: Provide ventilation, check the operation of the thermal relay, reduce the time of continuous operation.
• 💨 Oil release: Increase the volume of the oil separator or install an additional fine filter.
• ⚡ Humming without starting: Check the starting relay and the capacitor, the piston may be stuck.

Another problem may be condensate freezing in tubes when working in a cold room. Moisture in the air condenses and can turn into ice, blocking the passage. Installing a moisture separator (filter with silica gel) at the inlet will solve this problem.

Is it possible to use a compressor from a refrigerator to inflate tires?

Theoretically, it is possible, since it creates a pressure of up to 6-8 atmospheres, but this is impractical. The capacity (displacement) of a refrigeration compressor is very low, and inflating one tire will take a long time. In addition, it will quickly overheat. For these purposes, it is better to use specialized automotive compressors.

What oil is best to pour into a converted pump?

It is best to use special vacuum oils, but they are expensive. As a budget alternative, 10W-40 motor oil or gear oil has proven itself well. The main thing is to avoid oils with a large amount of additives, which can foam during active mixing.

Why does the pump throw oil into the hose?

This happens due to the design of the compressor, where the engine shaft and piston group are in an oil bath. During operation, the oil is whipped into foam and carried away by the air flow. The solution is to install a high-quality cyclonic oil separator or filter with a fine-porous filler (expanded clay, felt) at the outlet of the compressor.

How much vacuum can such a pump create?

A single-stage compressor from a refrigerator is capable of creating a residual pressure of about 0.05–0.1 atmospheres (500–100 mbar). This is enough for most household tasks, but for a deep vacuum (as in scientific laboratories) you will need a multi-stage system or a different type of pump.