Many home craftsmen often wonder whether it is possible to use an old one refrigerator compressor as a vacuum pump for various household needs. Indeed, the operating principle of a sealed unit makes it possible to create a vacuum, which theoretically opens up wide possibilities for its use for other purposes than its intended purpose. However, before proceeding with the alteration, it is necessary to clearly understand the physical limitations and design features of this mechanism.
The main task of such a home-made device often comes down to pumping air from air conditioning systems, vacuuming bags or conducting experiments. It is important to immediately note that a standard compressor is not a specialized vacuum degasser, and its performance in pumping mode will differ significantly from the factory performance during injection. Sealed housing hides nuances that can become critical if used incorrectly.
In this article we will examine in detail the technical aspects with which you will have to face if you decide to pursue this project. You will learn about real indicators of residual pressure, problems with lubrication and connection features. The maximum vacuum achievable by a household compressor rarely exceeds 0.05-0.08 MPa, which is significantly weaker than the indicators of industrial vacuum pumps.
Operating principle and physical limitations
A standard piston compressor installed in a refrigerator operates on the principle of volume displacement. The piston, moving inside the cylinder, sucks gas through the suction pipe and compresses it, throwing it out through the discharge pipe. When working with a vacuum, the process is inverted: the mechanism begins to pump out air from a closed volume connected to the inlet pipe. However, the design of the valves was initially designed for working with refrigerant, and not for creating a deep vacuum.
The main limitation is residual pressure. Unlike rotary vane pumps, the piston group is not able to provide the tightness required to achieve high vacuum. The gaps between the piston and the cylinder walls, as well as the bypass valves, begin to let air back in when a certain vacuum level is reached. This is a physical limit that cannot be overcome without a deep modernization of the mechanism.
In addition, it is worth taking into account thermal expansion. When working to create a vacuum, the compressor may heat up differently than during normal operation. The absence of freon flow, which in the refrigerator acts as a cooler for the windings and housing, leads to a change in the thermal regime. Temperature regime becomes a critical parameter that requires constant monitoring.
Why is it impossible to achieve absolute vacuum?
Absolute vacuum is unattainable in domestic conditions due to the evaporation of oils and microscopic leaks. Even industrial pumps leave residual pressure.
It is important to understand the difference between different types of compressors. Older models with heavier pistons may perform better than modern lighter versions. However, none of them are designed for long-term operation in deep vacuum mode without modifications.
Lubrication and oil problems
One of the most serious problems when using a refrigeration unit as a vacuum pump is the lubrication system. Inside the housing there is mineral or synthetic oilwhich is sprayed by the crankshaft to lubricate the rubbing pairs. When working on suction (vacuum), the effect of oil entrainment occurs: it begins to be actively sucked into the system that you are vacuuming, instead of remaining in the crankcase.
This leads to two negative consequences. Firstly, the oil level in the compressor drops, which threatens the mechanism jamming and bearing failure. Secondly, oil enters the vacuum system, contaminating it. If you use a pump to pump out condensate from an air conditioner or to work with electronics, the ingress of oil suspension is unacceptable.
The solution to the problem may be installation oil separator on the output path. This device allows the oil mist to condense and return the liquid back or collect it in a separate container. However, even with a filter, monitoring the lubricant level becomes a mandatory procedure before each start.
Some experts recommend replacing the standard oil with a more viscous one, but this is a controversial method. The mechanism is designed for a specific viscosity, and changing the lubrication parameters may lead to poor valve performance or overheating. It is better to use standard fluid, but monitor its quantity.
Connection and modification diagram
To transform a refrigeration compressor into a vacuum pump, minimal modification of the pipe system will be required. The standard scheme implies that one of the pipes (usually the thinner one that leads into the housing) becomes the vacuum inlet, and the other becomes the outlet. The third, often sealed, can be used for process needs or refueling, but is not involved in the basic circuit.
You will need the following components to assemble the installation:
- 🔧 High pressure hoses or reinforced tubes for connecting the pipes.
- 🔧 Check valve that prevents backflow air intake when the engine stops.
- 🔧 Vacuum gauge to monitor the degree of vacuum in the system.
- 🔧 Filter-moisture-oil separator to protect the system from lubricant release.
Connecting the electrical part also requires attention. The standard start-up scheme through PZR (Start-Protective Relay) must be saved. An attempt to power the motor directly, bypassing the relay and capacitor (if there is one), can lead to burnout of the starting winding. If the compressor is removed from the refrigerator, make sure that the relay is installed in the correct position, since many of them are sensitive to the angle of inclination.
Connection diagram:220V network -> PZR -> Compressor
Inlet pipe -> Evacuated object
Outlet pipe -> Atmosphere (through a filter)
Pay special attention to the tightness of the connections. Any microcrack in the hose or loose clamp will negate all efforts to create a vacuum. Use metal clamps and thread sealant, if used.
Specifications and performance
What to expect from performance? You should not rely on the performance of professional equipment. Household compressor with a capacity of 1/6 - 1/4 hp. capable of creating a residual pressure in the region of 50-80 mbar (0.05-0.08 atm). For comparison, specialized pumps reach 0.5 mbar and lower.
The pumping speed also leaves much to be desired. The volume of the combustion chamber of a household compressor is small, so the process of evacuation of a large volume will take considerable time. Below is a comparative table of characteristics.
| Parameter | Refrigeration compressor | Special. vacuum pump |
|---|---|---|
| Residual pressure | 0.05 - 0.08 MPa | 0.0005 - 0.001 MPa |
| Performance | Low (small volume) | High |
| Resource on vacuum | Reduced (lubrication problems) | Designed for mode |
| Noise | High | Medium/Low |
It is important to consider that when the vacuum limit is reached Device efficiency it drops to almost zero. Further operation of the motor will only lead to heating and wear, but not to improvement of the vacuum. This is why having a vacuum gauge is critical.
If your task requires higher performance, you may have to consider connecting two compressors in series, although this will significantly complicate the design and increase the requirements for the tightness of the system.
Areas of application of a homemade vacuum degasser
Despite the limitations, such a device has a number of useful applications in the home and garage. Most often it is used to service automotive systems. For example, to remove moisture and air from the car’s air conditioning system before refilling with freon. Although professionals use powerful pumps, a converted refrigerator is also suitable for a one-time home procedure.
Other uses:
- 🔨 Vacuum molding of plastic to create small parts or packaging.
- 🔨 Evacuation of air from containers for experiments.
- 🔨 Removing air bubbles from epoxy resin or silicone (degassing) in small volumes.
- 🔨 Checking the tightness of various containers and hoses.
In each case, it is necessary to evaluate the feasibility. To degas resin, for example, a fairly deep vacuum is required, which a conventional compressor may not be able to fully provide, but it will still partially remove bubbles.
⚠️ Attention: Never use a homemade vacuum pump to pump out aggressive chemicals, acids or alkalis. The vapors of these substances will destroy the motor windings and the insides of the mechanism instantly.
The device can also be used in a radio amateur workshop, although extreme caution with oil is required here. To work with electronics, it is better to use oil-free diaphragm pumps, but if there is no choice, install high-quality trap filters.
Safety and precautions
Working with vacuum and 220V electricity requires strict adherence to safety rules. The compressor housing is at mains potential, so grounding is mandatory. Lack of grounding can lead to electric shock, especially in conditions of high humidity or when working with metal containers.
In addition, the compressor housing itself experiences enormous external pressure when operating under vacuum. If the housing has microcracks or corrosion damage, it may collapse (implosion) with flying fragments. Visually inspect metal cylinder before starting operation.
☑️ Safety check before starting
Temperature conditions are also important. During prolonged operation, the case can heat up to 70-90 degrees. Do not touch the operating unit without protection and ensure good ventilation. Overheating can lead to decomposition of the oil and the formation of acids, which will damage the mechanism from the inside.
⚠️ Attention: If you smell burning or see sparking in the area of the start relay, immediately unplug the device. Further operation is prohibited.
Final conclusions and recommendations
Using a compressor from a refrigerator as a vacuum pump is a completely working, albeit compromise, option. It allows you to solve a number of problems without purchasing expensive equipment, but requires an understanding of physical processes and compliance with safety measures. The main enemies of such a system are oil and insufficient vacuum depth.
If you decide to implement this project, start small: assemble a circuit, check the tightness and measure the real indicators with a vacuum gauge. Don't expect miracles from a household appliance, but don't underestimate its potential if used correctly. Proper preparation and control of parameters will extend the life of the device.
Is it possible to use the compressor back for the refrigerator?
After operating in vacuum pump mode (especially with oil carryover), using the compressor in the refrigerator is highly not recommended due to the risk contamination of the system and changes in the properties of the lubricant.
Remember that any homemade product requires responsibility. If the task is critical and requires stable parameters, it is better to purchase a specialized tool. But for garage experiments and rare household needs, an old compressor is an excellent candidate for a second life.
What is the maximum vacuum you can get?
Usually this value is 0.05-0.08 MPa (residual pressure). Domestic piston compressors do not pull deeper due to design gaps.
Is it necessary to change the oil in the compressor?
It is not necessary to change it to a special vacuum one, but you will have to top up the usual one often, since some of it will go into the system. Keep an eye on the level.
Is it possible to pump water with this pump?
No, absolutely not. Water entering the compressor will cause corrosion and water hammer, leading to failure. This is a pump for gases only.
Does the compressor get very hot in this mode?
Yes, the heating can be significant, since the gas flow does not cool the motor as effectively as in the normal freon circulation mode. Need a break from work.
Is any compressor from a refrigerator suitable?
In principle, yes, but inverter models require complex electronics to start, so for conversion it is better to take the good old models with a start relay.