Repair of refrigeration equipment often requires not only the replacement of failed components, but also careful preparation of the system for operation. One of the critical stages, without which long-term operation of the unit is impossible, is the removal of moisture and air from the circuit. This process is called evacuation, and it must be performed using specialized equipment, in particular, a vacuum pump.
Attempts to start the refrigerator without first pumping out often lead to blockage of the capillary tube with ice or the formation of acids in the compressor oil. The moisture remaining in the system freezes in the narrow section of the capillary, blocking the circulation of the refrigerant. That is why professional craftsmen pay special attention to the pumping procedure, using vacuum pump and a pressure gauge station.
In this article we will look in detail at how to properly vacuum a refrigerator, what methods exist (dry and wet) and what to look for when working with different types of refrigerants. You will learn about the nuances of choosing an oil and the sequence of actions that are guaranteed to rid the system of non-condensable gases.
Why do you need to vacuum the refrigeration system
The main purpose of vacuuming is to reduce the pressure in the circuit below atmospheric to remove water and air vapor. Water entering the system can be in three states: liquid, steam or ice. During normal operation of the refrigerator, water circulates along with oil and refrigerant, but when passing through the throttling device (capillary tube), the temperature drops sharply.
If there is moisture in the system, it freezes precisely at the throttling point, forming an ice plug. This phenomenon is known as hydraulic hammer or simply blockage, which stops cooling. In addition, water reacts chemically with refrigerants and oil, forming aggressive acids that destroy the compressor motor windings from the inside.
The air remaining in the system contains nitrogen and oxygen. Nitrogen is a non-condensable gas that increases the overall pressure in the condenser, causing the compressor to work overload. Oxygen oxidizes the oil, leading to the formation of sludge and resins that clog the filter drier.
⚠️ Attention: Never use a household vacuum cleaner to vacuum the refrigerator. It is not capable of creating the necessary deep vacuum and can become a source of sparking, which is dangerous when working with flammable refrigerants.
High-quality removal of moisture and gases is possible only when a certain level of residual pressure is reached. For household refrigerators, this figure is usually less than 500 microns (0.5 mm Hg), which cannot be ensured without a professional. Ignoring this stage significantly reduces the life of the repaired unit. vacuum pump. Ignoring this stage significantly reduces the life of the repaired unit.
Necessary equipment and tools
To carry out high-quality vacuuming, you will need a specific set of tools. The basic element is the vacuum pump itself. There are single-stage and two-stage models. For household repairs, a single-stage pump with a capacity of about 100 liters per minute is most often sufficient, but two-stage models create a deeper vacuum and work faster.
The second important element is the pressure gauge station (manifold). It allows you to control the pressure in the system and connect cylinders with refrigerant or nitrogen. The manifold must be equipped with a vacuum gauge, the scale of which is graduated in microns or inches of mercury, since conventional pressure gauges do not indicate deep vacuum.
You will also need connecting hoses. It is advisable to use low-loss hoses, which minimize the entry of air into the system when disconnecting. Don't forget about the tools for working with copper tubes: a pipe cutter, rolling and soldering torch.
- 🛠️ Vacuum pump (one- or two-stage) to create a vacuum.
- 📊 Manometric manifold with a vacuum gauge to control parameters.
- 🔧 A set of hoses and valves for connecting to service ports.
- 🔥 Gas torch and solder for sealing connections.
It is important to monitor the condition of the oil in the vacuum pump. It must be transparent before starting work. If the oil becomes cloudy or blackened, it must be replaced, since it is already saturated with moisture and will not be able to effectively absorb water vapor from the refrigerator system.
Preparing the refrigerator for pumping
Before starting vacuuming, it is necessary to prepare the unit itself. If the compressor or filter drier is replaced, the system will already be depressurized. In this case, it is important to minimize the time during which the pipes are open to prevent saturation of the internal walls with moisture from the surrounding air.
The process begins with the installation of a new filter-drier. This element is critically important, since it is it that finally removes remaining moisture and acid from the refrigerant. The filter is sealed immediately after removal from the packaging so that it does not have time to become saturated with atmospheric power. Pay attention to the flow direction indicated by the arrow on the filter housing.
Next, the pressure gauge station is connected. The blue hose (low pressure) is connected to the compressor suction line, the red (high pressure) hose is connected to the discharge line or to the fitting on the condenser, if there is access there. The yellow hose connects to the vacuum pump.
Check the tightness of all connections before turning on the pump. Open the valves on the manifold and check that the vacuum gauge needle begins to move. If the arrow is still in place, check whether the taps are open and whether the hose nuts are tightly tightened.
Vacuum technology: step-by-step instructions
The process of pumping out air and moisture requires compliance with a certain sequence of actions. First, make sure that the valves on the manifold are closed and the hoses are connected correctly. Turn on the vacuum pump and only then open the valves on the manifold. This will prevent oil from flowing back from the pump into the refrigerator system.
The evacuation time depends on the volume of the system and the power of the pump. For a domestic refrigerator, the minimum pump operating time is 15–20 minutes. However, time is not the only criterion. The main indicator is the level of residual pressure. It is necessary to reach a value at which the vacuum gauge needle stops falling and freezes at below 500 microns.
After achieving the required vacuum, close the valves on the manifold and turn off the pump. Now comes the stage of testing for leaks. Leave the system alone for 15–20 minutes. If the needle on the vacuum gauge begins to creep up (the pressure increases), it means that there is a leak in the system or there is moisture remaining that is evaporating.
☑️ Checking readiness for vacuuming
If the pressure increases, the process must be repeated. Sometimes a procedure called "purge" or "triple-purge" is required, where the system is filled with a small amount of refrigerant or nitrogen and then evacuated again. This helps displace remaining moisture.
| Parameter | Value / Description | Criticality |
|---|---|---|
| Residual pressure | < 500 microns (0.5 mm Hg. Art.) | High |
| Pumping time | Minimum 15-20 minutes | Medium |
| Oil condition | Transparent, without emulsion | High |
| Vacuum stability | No change for 20 minutes | Critical |
Only after the system holds a stable vacuum, you can begin charging with refrigerant. Refilling should be done immediately after checking so that air does not enter the system. The hoses are disconnected under a slight positive pressure of freon to prevent air leaks.
Features of working with different refrigerants
Different types of refrigerants require different approaches to preparing the system. Old refrigerators operating on R12 or R134aare less sensitive to microscopic moisture residues than modern models. However, this does not mean that they can be neglected. For R134a, it is necessary to use synthetic oils (POE), which are extremely hygroscopic, that is, they actively absorb moisture from the air.
Modern refrigerators are often filled with hydrocarbon refrigerants, such as R600a (isobutane). They work with mineral oils but are flammable. When vacuuming such systems, it is important not only to remove moisture, but also to displace air as much as possible in order to avoid the formation of an explosive mixture inside the circuit during the first start-up.
⚠️ Attention: When working with R600a, it is strictly forbidden to turn on the compressor if there is air in the system. This may cause an explosion. Evacuation should be especially thorough, with control of the intrinsic safety of the equipment.
Why should you not mix oils?
Synthetic oils (POE, PAG) and mineral oils do not mix with each other. If mineral oil from an old compressor is left in a system with R134a (synthetic), this will lead to the formation of clots that clog the capillary.
For systems with R404A or R407Cwhich are often used in commercial equipment, the requirements for system cleanliness are even higher. These mixtures are sensitive to changes in composition, so any manipulations must be carried out carefully so as not to disturb the proportions of the components.
Common mistakes when vacuuming
One of the most common mistakes is insufficient pump operating time. Novice craftsmen often focus only on time, forgetting to control the vacuum gauge. 10 minutes of running a weak pump on a large refrigerator will not give any effect other than creating the appearance of operation.
The second mistake is using old or wet oil in the vacuum pump. The oil in the pump acts as a sealant and absorber of water vapor. If it is already saturated with moisture, it will stop “pulling” the vacuum, and you will run the pump for hours to no avail. Change the oil in the pump regularly, especially after working with “wet” systems.
The third mistake is turning off the pump without closing the valves. This leads to the backflow of oil vapor from the pump into the refrigerator circuit. Oil vapor will settle on the walls of the evaporator and condenser, impairing heat transfer and creating a film that is difficult to remove. Always close the manifold valve first, and only then turn off the pump.
- ❌ Ignoring the vacuum gauge readings and working “by eye.”
- ❌ Using low-quality hoses that allow air to pass through.
- ❌ Trying to vacuum the system while the compressor is running refrigerator.
It is also considered a mistake to neglect to replace the filter-drier. The vacuum pump removes free moisture, but cannot remove water chemically bound in the old filter. Installing an old filter will negate all vacuuming efforts.
Frequently asked questions (FAQ)
Is it possible to vacuum a refrigerator with a regular car compressor?
No, a car compressor is designed to build up pressure, and not to reduce it (create a vacuum). It will not be able to remove moisture and air from the system, which will lead to breakdown of the refrigerator after refueling.
How long should you keep the vacuum in the system?
The minimum operating time of the pump is 15–20 minutes. However (what is more important) is the stability of the vacuum gauge readings. The system should maintain a vacuum (the arrow should not creep up) for 15–20 minutes after turning off the pump.
What to do if the vacuum does not hold and the pressure rises?
This indicates a leak in the system or the presence of a large amount of moisture. It is necessary to check all soldered connections with soapy water (foam). If there are no leaks, it may be necessary to repeat the evacuation procedure with warming up the evaporator or replace the filter drier.
Is it necessary to heat the compressor during evacuation?
Warming the compressor (for example, with a hairdryer or lamp) is sometimes used to accelerate the evaporation of moisture from the oil inside the compressor itself. This helps to achieve a deeper vacuum, but requires care not to damage the insulation of the windings.