The process of restoring the functionality of a refrigeration unit after a freon leak or replacing a compressor requires strict adherence to technological standards. One of the critical operations is removing moisture and air from the system. Vacuuming The circuit helps prevent the formation of ice plugs and oil oxidation, which directly affects the durability of the equipment.
Many amateur craftsmen neglect this stage, relying on purging with refrigerant, which is a gross mistake. The remaining moisture in the system, when in contact with the refrigerant and oil, can enter into a chemical reaction, forming aggressive acids. These connections destroy the compressor motor windings and clog the capillary tube.
To perform high-quality pumping, you will need specialized equipment: two-stage vacuum pump, a pressure gauge station and hoses that can withstand low pressure. It is important to understand that household vacuum cleaners or compressors for aquariums are not capable of creating the necessary vacuum. Below we will analyze in detail the entire process of preparing and carrying out work.
Principle of operation and the need for vacuuming
The main purpose of creating a deep vacuum in the refrigerator circuit is to reduce the boiling point of water. At atmospheric pressure, water boils at 100°C, but under rarefaction conditions this threshold drops to room temperature and below. This allows you to turn moisture into steam and remove it from the system before Freon is added there. If you ignore this step, the remaining moisture will freeze in the throttling zone (usually the exit from the capillary tube). The resulting ice plug will block the circulation of the refrigerant, and the refrigerator will stop freezing. In addition, air containing nitrogen and oxygen increases the condensation pressure, causing the compressor to work with overload. freon.
If this step is ignored, the remaining moisture will freeze in the throttling zone (usually the outlet of the capillary tube). The resulting ice plug will block the circulation of the refrigerant, and the refrigerator will stop freezing. In addition, air containing nitrogen and oxygen increases the condensation pressure, causing the compressor to work overload.
⚠️ Attention: An attempt to refill the refrigerator without preliminary evacuation in 90% of cases leads to repeated failure after several weeks or months of operation. Oxygen in the system oxidizes the mineral oil, turning it into a thick mass.
Modern refrigerants, such as R600a (isobutane) or R134aare extremely sensitive to the cleanliness of the system. Even a microscopic amount of moisture can disrupt their thermodynamic properties. Therefore, using a vacuum pump is not a recommendation, but a mandatory requirement of the repair technology.
Why can’t you blow it with freon?
The method of “pushing” the system with freon is effective only for removing large particles of dirt, but is absolutely useless against moisture. Moisture is adsorbed on the walls of the tubes and in the oil, and it is impossible to displace it with gas without changing pressure and temperature.
Necessary equipment and tools
To successfully carry out the work, you will need to assemble a set of specialized tools. The basic element is the vacuum pump. For household refrigerators, the optimal choice would be two-stage model with a capacity of 45 to 60 liters per minute. Single-stage pumps will also cope, but the process will take longer, and the residual pressure will be higher.
The second important element is the pressure manifold. You'll need a version with a blue hose (low pressure) and a red hose (high pressure), although vacuuming often requires just the blue hose. Hoses must be equipped with threaded ends compatible with the service port of your refrigerator or solder adapters.
- 🛠️ Vacuum pump (oil, two-stage preferred)
- 🔧 Gauge station with hose kit
- ⚖️ Electronic scales for accurate refilling of freon
- 🔥 Burner and solder for sealing the system after pumping
Also do not forget to prepare tools for soldering: gas torch, copper solder and flux. After creating a vacuum, it is necessary to seal the filling tube tightly while the pump continues to operate or immediately after closing the valve. The presence of a leak detector at the stage of checking the tightness before vacuuming is also highly desirable.
Preparing the refrigeration system for pumping
Before connecting the pump, you must ensure that the circuit is completely sealed. Evacuating a leaking system is pointless: you will pump the atmosphere, and not remove moisture from the inside. Check all solder joints and possible leaks using nitrogen or soapy water.
If there is old refrigerant left in the system, it should be bled off. It is better to do this through a puncture of the fitting or service valve, observing safety precautions. After this, the filter drier is replaced. This element disposable and must be replaced whenever the circuit is opened, since the old adsorbent is already saturated with moisture.
The pump is connected through a service valve or a pre-soldered fitting. Make sure connections are tight. Before starting the pump, check the oil level in its inspection window. If you are using a manifold, make sure that the valves on it are closed before starting the equipment.
☑️ Preparation for vacuuming
Process technology: step-by-step instructions
The pumping process itself requires care and control of indicators. Connect the hose from the pump to the service port of the refrigerator. Open the valve on the pressure gauge station (blue) and only then turn on the vacuum pump. You should hear a change in the sound of the engine - it will become more smooth.
During operation, the vacuum gauge needle will begin to drop into the negative zone. Your task is to achieve a pressure close to a technical vacuum. For household refrigerators, the target value is -1 bar (or about 750-760 mm Hg depending on the scale of the device). You should not focus only on time; it is the pressure indicator that is important.
The duration of the process depends on the volume of the system and the power of the pump. Typically a household refrigerator requires 20 to 40 minutes of active pumping. However, professionals recommend carrying out the procedure longer, sometimes up to an hour, to ensure that all moisture evaporates from hard-to-reach places in the evaporator.
⚠️ Attention: Never turn off the pump by simply turning off the valve if you are planning a long break. Backflow of air through the pump seals can ruin the job. It is better to keep the pump on or use a shut-off valve.
When the desired pressure is reached, close the valve on the manifold. Now you can turn off the pump. Quickly but carefully, solder the copper filler tube while the system maintains a vacuum. This will prevent air from getting inside when dismantling the hoses.
Control parameters and pressure table
Understanding what pressure to be considered normal requires knowledge of the physics of the process. Vacuum is the absence of pressure. On a low pressure gauge (blue), the scale is often graduated so that zero is atmospheric pressure, and minus 1 (or 30 inHg) is deep vacuum.
It is important to distinguish between residual pressure and the speed at which it is reached. A good pump should confidently go into minus within the first 5-10 minutes. If the arrow freezes at a certain value and does not move further, there may be a leak in the system or the pump requires an oil change.
| Equipment type | Residual pressure (bar) | Pumping time (min) | Note |
|---|---|---|---|
| Household refrigerator (1 compressor) | -0.95 ... -1.0 | 20-30 | Standard procedure |
| No Frost refrigerator | -0.98 ... -1.0 | 30-45 | Complex defrosting system |
| Industrial display case | -0.98 ... -1.0 | 60+ | Large circuit volume |
| Double-circuit refrigerator | -0.95 ... -1.0 | 40-50 | Pumping through both circuits |
Please note that values may vary slightly depending on your gauge calibration and the barometric pressure in your area. The main thing is the stability of the readings. If, after stopping the pump and closing the valve, the arrow begins to creep up, it means that the tightness of the system is broken.
Completion of work and charging with refrigerant
After the system is securely sealed, you can proceed to charging. For this, the same manometric manifold is used, but now a freon cylinder is connected to the red or blue port (in the liquid phase). Refilling is carried out strictly by weight, according to the nameplate on the refrigerator.
Turn on the compressor and supply refrigerant in small portions, controlling the electric motor current and the condenser temperature. Excess or lack of freon is equally harmful to the system. Refilling can lead to water hammer, and underfilling can lead to overheating of the compressor.
- ❄️ Monitor the evaporator temperature (should be uniform)
- 🔌 Monitor the current consumption (not higher than the nominal value)
- 👂 Listen to the operation of the compressor (no gurgling)
After refueling, let the refrigerator run for several hours in idle mode. Make sure it gets up to temperature and the thermostat turns off. Only after successful testing can the repair be considered complete.
Is it possible to use a car pump for vacuuming?
No, ordinary car compressors pump air, but do not create a vacuum. There are reversible models, but their performance and vacuum depth are insufficient for refrigeration technology. A specialized vacuum pump is required.
How long do you need to hold the vacuum?
The minimum active pumping time is 15-20 minutes for small systems. However, the optimal time is considered to be 30-40 minutes to ensure the evaporation of moisture from the oil and the walls of the tubes.
What to do if the vacuum does not hold?
If the pressure rises after stopping the pump, then there is a fistula in the system. It is necessary to look for the leak again, most likely using nitrogen under pressure, and eliminate it by soldering.
Is it necessary to heat the compressor during evacuation?
Yes, lightly heating the compressor housing (with a hairdryer or lamp) to 50-60°C helps evaporate the moisture contained in the oil inside the crankcase and remove it through the pump.
Which pump is better: one-stage or two-stage?
For refrigerators, a two-stage pump is preferable. It creates a deeper vacuum (less residual pressure), which is critical for high-quality drying of the system.