Loss of cooling capacity in a commercial or industrial refrigerator often indicates a refrigerant leak. Freon R404A Is the standard for freezers and chest freezers due to its efficiency at low evaporation temperatures. However, the process of its injection requires strict adherence to technology, since it is sensitive to disturbances in the phase composition. Freon R404A is a quasi-azeotropic mixture. Independent intervention in the circuit without the appropriate equipment and knowledge can lead to compressor failure or explosive situation. The pressure in the system can reach critical values, and the presence of moisture in the circuit causes the formation of acids that destroy the motor windings. Therefore, before starting work, it is necessary to assess the risks and make sure that you have specialized tools. quasi-azeotropic mixture, sensitive to disturbances in phase composition.
Individual intervention in the circuit without the appropriate equipment and knowledge can lead to compressor failure or an explosive situation. The pressure in the system can reach critical values, and the presence of moisture in the circuit causes the formation of acids that destroy the motor windings. Therefore, before starting work, it is necessary to assess the risks and make sure that specialized tools are available.
In this article we will analyze the technical nuances of working with R404A refrigerant, consider the stages of evacuation and charging, and also point out the critical mistakes that beginners make. Refilling R404A is possible only in the liquid phasewhat distinguishes this process from working with household refrigerants such as R134a. Ignoring this rule will lead to a change in the composition of the mixture and loss of properties.
Features of the R404A refrigerant and equipment preparation
The refrigerant R404A is a mixture of three components: R125, R143a and R134a. This is a pseudoazeotropic composition, which, if leaked, changes its fractional structure if refueling is done incorrectly. Unlike pure substances, the mixture has a temperature glide, which must be taken into account when setting up a thermostatic expansion valve or a capillary pipe. The pressure gauge scale should reach at least 35-40 bar, since the condensation pressure of R404A is significantly higher than that of household analogues. You also need high-precision scales, a vacuum pump with a capacity of at least 4 cubic meters per hour and a leak detector. thermostatic valve (TRV) or capillary pipe.
To work, you will need a specialized station with a pressure manifold designed for high pressure. The pressure gauge scale should reach at least 35-40 bar, since the condensation pressure of R404A is significantly higher than that of household analogues. You also need high-precision scales, a vacuum pump with a capacity of at least 4 cubic meters per hour and a leak detector.
⚠️ Attention: R404A cylinders are equipped with a dip tube. To refill correctly, the cylinder must be turned upside down so that liquid, not gas, enters the system.
Preparation of the workplace includes checking the tightness of the hose connections. Use only 1/4" hoses designed for HFC refrigerants. Rubber seals must be made of material that is resistant to synthetic oils, which are used in modern compressors.
Finding and eliminating leaks before refueling
Simply adding gas to a system where there is a fistula is a waste of time and money. Before vacuuming, it is necessary to localize the leak. Damage often occurs at solder joints, on the condenser or in the evaporator due to vibration or corrosion. To search, use pressurized nitrogen or an electronic leak detector configured for halogens.
If a leak is found, the damaged area is cut out and resoldered using copper-phosphorus solder. It is important not to overheat the tube so that carbon deposits do not form inside, which will later clog the capillary. After soldering, the system must be purged with nitrogen to remove oxides.
- 🔍 Visual inspection for the presence of oil stains (oil comes out along with freon).
- 🔍 Checking all threaded connections and ports with a soap solution.
- 🔍 Use an ultraviolet lamp, if a fluorescent marker remains in the system.
After eliminating the defect, nitrogen pressure testing is carried out. The pressure rises to 20-25 bar (for low-temperature systems) and is maintained for at least 24 hours. A pressure drop of even 0.1 bar indicates the presence of a micro-leak that needs to be found.
The process of evacuation of the system
Evacuation is the most important stage on which the durability of the compressor depends. Residual moisture in the circuit, upon contact with refrigerant and oil, forms hydrochloric acid, which corrodes windings and metal parts. In addition, the water freezes in the capillary, forming an ice plug that blocks circulation.
Connect the vacuum pump to the service port. Pumping time depends on the volume of the system and the power of the pump, but usually ranges from 30 minutes to 1 hour. It is critical to monitor the residual pressure with a manifold gauge. For R404A, the residual pressure should be less than 50 microns (0.05 mmHg), although in practice they often focus on the arrow in the green vacuum zone.
☑️ Evacuation checklist
After reaching a vacuum, close the valves on the manifold and turn off the pump. Observe the pressure gauge for 15-20 minutes. If the arrow creeps up, there is a leak in the system or moisture is evaporating. If the pressure increases, the procedure must be repeated, possibly using a nitrogen purge to “pull out” the moisture.
⚠️ Attention: Never turn on the compressor without a vacuum or with air in the system. This can lead to insulation breakdown and immediate failure of the unit.
R404A refrigerant charging technology
As mentioned earlier, R404A requires charging in the liquid phase. This is due to the fact that the components of the mixture have different volatility. If you start gas, more of the low-boiling component will enter the system, and a “heavy” fraction will remain in the cylinder, which will upset the balance of the mixture. Therefore, the cylinder is placed on the scales and turned upside down.
Open the valve on the cylinder and slightly open the valve on the hose to displace air from the line (bleeding). Then quickly connect the hose to the refrigerator's service port. Open the valve on the manifold in small portions, monitoring the scales. Refueling is carried out strictly according to the weight indicated on the compressor nameplate or in the technical documentation.
Calculation example:Refueling mass: 850 grams.
Weight of an empty cylinder with a hose: 5.0 kg.
Target weight on scales: 4.15 kg (5.0 - 0.85).
During the charging process, the compressor can be started briefly so that the refrigerant is more actively absorbed into the system, but this must be done carefully, monitoring the suction pressure. Avoid water hammer - liquid freon should not enter the compressor cylinder in large volumes.
What to do if the scales show incorrectly?
Before starting work, be sure to tare (zero) the scales taking into account the weight of the hoses. If the scale is old, check its calibration with a known weight. An error of 10-20 grams can significantly affect the operation of the system.
Control of pressure and superheat temperature
After the main refueling, it is necessary to adjust the system for steam superheating. This is a parameter showing how much the gas temperature at the outlet of the evaporator is higher than the boiling point. For R404A, normal superheat is 5-8 degrees Celsius. Insufficient overheating threatens liquid entering the compressor, and excessive overheating can lead to engine overheating.
Measure the temperature of the tube at the outlet of the evaporator (with a clothespin thermometer) and the suction pressure (with a pressure gauge). Convert pressure to boiling point using the saturation table for R404A. The difference between the actual temperature of the tube and the boiling point is overheating.
| Parameter | Normal value | Critical deviation | Possible cause |
|---|---|---|---|
| Pressure suction | 1.5 - 3.0 bar | < 0.5 bar or > 4.5 bar | Underfilling / overflow of freon |
| Discharge pressure | 12 - 16 bar | > 20 bar | Air in the system, dirty condenser |
| Discharge temperature | 70 - 90 °C | > 110 °C | Insufficient superheat, valve breakdown |
| Compressor current | According to nameplate (±10%) | Above nominal | Overload, low voltage |