Repair of refrigeration equipment often requires intervention in a closed circuit circuit where the refrigerant circulates. If there is a freon leak or the compressor has been replaced, air and moisture inevitably remain inside the system. It is these components that are the main enemies of effective operation refrigeration unit, causing blockage of the capillary tube and oxidation of the motor windings.
The process of removing gaseous substances and water vapor from the system is called evacuation. Without performing this procedure, it is absolutely impossible to start the equipment, since residual moisture at low temperatures will turn into ice plugs blocking circulation freon. It is possible to perform this operation at home, but you will need a specific tool and strict adherence to technology.
Many amateur craftsmen mistakenly believe that it is enough to simply bleed off the old gas and start a new one. This is a fatal error that leads to the failure of a new compressor in a matter of hours. Understanding the physical processes occurring inside the tubes and using the right equipment is the key to successfully restoring the functionality of your equipment.
Physics of the process and the need to remove moisture
Atmospheric air contains water vapor, which is invisible under normal conditions. However, inside the refrigeration circuit, where the temperature can drop below -20°C, this vapor instantly crystallizes. The resulting microcrystals of ice can completely block the thinnest channel capillary tube, which will lead to a stop in cooling.
In addition, the oxygen contained in the air reacts with oil and metals at high discharge temperatures. This causes the formation of acids and varnish deposits, which destroy the insulation of the motor windings. Evacuation allows you to reduce the pressure in the system to a level at which water boils at room temperature and is removed in the form of steam.
⚠️ Attention: Residual moisture in the system is the main cause of corrosion of the internal parts of the compressor. Even a small amount of water can cause the piston group to jam after several months of operation.
The effectiveness of moisture removal directly depends on the depth of the vacuum created. The lower the pressure, the lower the temperature at which water boils. To ensure high-quality drying of the circuit, it is necessary to achieve indicators that conventional household appliances cannot provide. It requires the use of specialized equipment capable of pumping out air to a state close to an absolute vacuum.
Necessary equipment and tool preparation
To carry out the work, you will need to collect a minimum set of professional tools. The use of automobile pumps or medical syringes is unacceptable, since they are not capable of creating the required vacuum. The basic element is vacuum pumpwhich can be vane-rotor or membrane.
Valve-rotor models are considered the standard for repairing household appliances. They provide high pumping speed and deep vacuum. Membrane analogues are quieter, but their productivity is often lower, which increases the procedure time. It is also critical to have a pressure gauge station (manifold) to monitor the pressure in the system.
Do not forget to prepare the connecting hoses. They should be designed specifically for vacuuming and working with freon, and not for water or air. Conventional watering hoses can collapse under vacuum or leak air through their walls, reducing all efforts to zero. To connect to the service ports, nipples of the appropriate diameter are used.
Step-by-step instructions for evacuating the system
First step is always the preparation of the system. If there is still old refrigerant in the circuit, it must be released through a piercing valve or service valve. This should be done in a well-ventilated area, since the gas is heavier than air and can displace oxygen. After relieving the pressure, new connections are soldered or the compressor is replaced.
Next is the connection of the vacuum pump. The hose from the pump is connected to the central inlet of the pressure manifold. The blue hose (low pressure) connects to the service port on the refrigerator suction line. The red hose (high pressure) may not be used in this process if there are no separate valves in the system, but it is better to keep it closed.
The pumping process is as follows:
- 🔧 Open the valve on the blue manifold pressure gauge.
- 🔧 Turn on the vacuum pump and observe pressure gauge arrow.
- 🔧 Bring the pressure to the lowest possible value (usually about -1 bar or 0 Pa).
- 🔧 Leave the pump running for the time necessary for the moisture to evaporate (from 30 minutes to several hours).
It is important to understand that the process cannot be stopped immediately after reaching a vacuum. At this time, active evaporation of moisture from the oil and from the walls of the tubes occurs. If you turn off the pump prematurely, water will remain in the system in liquid form. Only after a long exposure under vacuum can the manifold valve be closed and the equipment turned off.
☑️ Checklist before starting the pump
Conformity table for oils and refrigerants
When replacing a compressor or carrying out repairs, the issue of material compatibility often arises. Different types of refrigerants require the use of strictly defined oils. If you mix mineral oil with synthetic oil or use the wrong brand, coagulation (curling) of the lubricant will occur, which will lead to rapid wear of the rubbing parts.
The table below shows the main correspondences that the master needs to know:
| Type of refrigerant | Type of required oils | Compatibility features |
|---|---|---|
| R12, R134a | Mineral (MO) or Alkylbenzene (AB) | Classic oils, hygroscopic, require careful vacuuming. |
| R410A, R407C | Polyester (POE) | Very hygroscopic, absorb moisture in minutes, require instant sealing. |
| R600a (Isobutane) | Mineral (MO) | Explosive, requires special care when soldering and vacuuming. |
Pay attention to the line with polyester oils (POE). They have extremely high hygroscopicity. This means that they absorb moisture from the air literally before our eyes. If you are working with a modern refrigerant, the time of open contact of the system with the atmosphere should be minimal.
⚠️ Attention: When working with R600a (isobutane), make sure that there are no open sources of fire in the room, and that power tools do not spark. This gas is explosive in concentrations with air.
Tightness control and holding time
After evacuation is completed, it is necessary to ensure that the system is tight. There is a common mistake: technicians begin refueling immediately after turning off the pump. This cannot be done. It is necessary to carry out a pressure drop test, the so-called “vacuum pressure test”.
Close the valve of the pressure gauge station, disconnect the pump (or close the valve on the pump itself, if the design allows) and leave the system alone. Monitor the pressure gauge needle for 15–30 minutes. If the arrow starts to creep up, it means there is a leak in the system. A microcrack in the solder or a poor connection will let air in.
Why can the needle tremble?
A slight trembling of the pressure gauge needle can be caused by vibration of the pump itself or thermal expansion of the metal. However, a smooth and confident rise in readings is always a sign of a leak.
If the vacuum remains stable, you can move on to the next stage. The holding time under vacuum also depends on the volume of the system. For household refrigerators, 30–40 minutes of active pump operation after reaching operating pressure is sufficient. For industrial chambers or systems with long routes, this time can increase to several hours.
Filling with refrigerant and completing work
The final stage is filling the circuit with working gas. This must be done without breaking the created vacuum. The freon cylinder is connected to the manifold, and the gas is released into the system under its own pressure. Charging with the liquid phase (inverted cylinder) is allowed only for certain types of refrigerants and requires the presence of scales for accurate dosing.
The amount of refrigerant is indicated on a technical sticker, usually located on the back wall of the refrigerator or inside the chamber. Overdosing is just as dangerous as underdosing. Excess gas will lead to increased condensation pressure and overload of the compressor, and too little will lead to insufficient cooling and overheating of the motor.
After refueling, it is necessary to solder the filling tube. This must be done quickly, using a plug clamp so as not to release the gas. Then a test run is carried out. During the first minutes of operation, monitor the pressure gauge readings and the temperature of the tubes. The suction tube should freeze, and the discharge tube should be hot, but not hot.
Frequent errors and ways to eliminate them
Even experienced specialists sometimes make mistakes that negate all the work. One of the most common is using wet or dirty hoses. Before starting work, all tools must be dry and clean. Dust or water droplets entering the circuit is unacceptable.
Another mistake is neglecting to replace the filter-drier. This element is designed to trap microscopic particles of moisture and debris. If the circuit depressurizes, the filter-drier required must be replaced, since its sorbent is already saturated with moisture from the air and can no longer work effectively.
It is also worth mentioning the error with the choice of pump. Using a pump with insufficient capacity for a system in which water may have entered will result in the moisture simply not having time to evaporate. In such cases, it is recommended to use two-stage vacuum pumps that create a deeper vacuum.
Is it possible to vacuum a refrigerator with a car pump?
No, a car pump creates excess pressure to inflate tires, not a vacuum. Even if it works in the opposite direction, its performance and vacuum depth are not sufficient to remove moisture from the refrigeration circuit.
How long do you need to keep the vacuum?
The minimum time for active operation of the pump after reaching a vacuum is 30 minutes. However, if there is a suspicion of a large amount of moisture, the time can be increased to 2-3 hours. The main thing is the stability of the pressure gauge readings after shutdown.
What to do if the vacuum does not hold?
It is necessary to recheck all solder joints using a soap solution or a special leak detector. Also check the tightness of the hoses to the service ports. The leak must be found and eliminated before refueling.
Is it necessary to heat the compressor during evacuation?
Warming the compressor (for example, with a hairdryer or lamp) during evacuation helps evaporate moisture trapped in the oil. This is a useful procedure, especially if the system has been open for a long time, but requires care not to damage the insulation of the wires.