Circuit leakage is one of the most difficult and expensive problems faced by owners of household appliances. If the refrigerator has stopped freezing, but the compressor sounds like it is working normally, it is often required checking the system for leaks pressure testing. This process allows you to accurately determine the presence of microcracks or breaks in pipelines hidden in a foamed space.
The procedure requires not only special tools, but also strict adherence to safety precautions, since the work is carried out with gas under pressure. Crimping a refrigerator is the first and main stage of diagnosis, without which further repairs impossible. Ignoring this step can lead to a waste of time and money on refilling with freon, which will again evaporate through a leaky connection.
In this article we will analyze in detail the technology of the work, the necessary equipment and nuances that only professional craftsmen know. You will learn how to properly prepare the system, what pressure to use for different types of refrigerants and how to find a leak using a soap solution or helium.
Necessary equipment and preparation for work
Before starting any manipulations with the refrigeration circuit, it is necessary to prepare the workplace and tools. The main device is pressure gauge station, which allows you to control the pressure in the system in real time. Without an accurate pressure gauge, it is impossible to guarantee the quality of the test, since even a slight deviation of the arrow may indicate a leak.
You will also need a cylinder of dry nitrogen, which is the standard for pressure testing due to its inertness and lack of moisture. The use of oxygen or air from the compressor is strictly prohibited, as this can lead to the formation of an explosive mixture with oil residues or an explosion during compressor operation.
⚠️ Attention: Nitrogen is in the cylinder under high pressure. Be sure to use a reducer to reduce the pressure to operating values so as not to rupture the thin-walled tubes of the evaporator or condenser.
To seal the system, you will need special clamping sleeves (sealed couplings) for a 6 mm or 8 mm tube, as well as tools for their installation - a pipe cutter and a rolling machine. Don’t forget to prepare a bowl of water or a spray bottle with soapy water to search for gas outlets.
Dismantling and cutting off the compressor
The first stage of work is preparing the refrigeration unit. If you plan to carry out pressure testing, the compressor is usually already disconnected from the electrical network. It is necessary to gain access to the service pipe or cut the filling tube.
If the unit does not have a standard Schrader valve, it must be installed. To do this, the tip of the filling tube is cut off, and a valve is installed in its place by soldering or mechanical crimping. This allows you to repeatedly connect the pressure manifold without compromising the tightness of the system in the future.
- 🔧 Cut the charging tube at a distance of 5-7 cm from the compressor body using a sharp pipe cutter.
- 🔧 Install the brass fitting or valve, making sure it sits tightly on the copper.
- 🔧 Solder the connection with a torch using silver solder to ensure reliability.
After installing the valve, the system is considered ready to connect an external pressure source. Filter drier in this case it serves as a barrier, but during long-term crimping it is better to replace it with a new one after completion of the work.
Connecting nitrogen and creating pressure
The process of creating pressure in the circuit requires care. Connect the hose from the nitrogen cylinder to the service valve. Before opening the valve on the cylinder, make sure that the valve on the pressure gauge is closed to avoid a sudden surge in pressure that could damage the device.
When opening the cylinder valve, gradually increase the pressure, following the readings of the pressure gauge needle. For household refrigerators running on R134a or R600a freon, the operating pressure during pressure testing is usually from 8 to 12 atmospheres. Exceeding the value of 15 atmospheres is dangerous for aluminum evaporators.
There is a table of recommended pressures for different types of systems, which should be followed:
| Refrigerant type | Working pressure (atm) | Maximum test (atm) | Features |
|---|---|---|---|
| R134a | 8 - 10 | 12 | Standard for modern models |
| R600a (Isobutane) | 6 - 8 | 10 | Explosive, requires caution |
| R12 (Outdated) | 10 - 12 | 15 | Found in old equipment |
| R404a (Industrial) | 15 - 18 | 25 | For freezers |
After reaching the required pressure, close the valve on the cylinder, then release the pressure from the hose and disconnect it from the system. The circuit is now under pressure and the pressure gauge should show a stable value. Any drop in the needle will indicate a leak.
Searching for leaks: methods and technologies
If the pressure gauge needle creeps down, you need to find the location of the leak. The simplest and most accessible method is to use soap solution. Apply thick soap suds to all visible connections, solders, capacitor and tube insertion points into the housing.
Be careful of the surface. At the point where the gas escapes, characteristic bubbles will inflate and increase in size. This method is effective for large leaks, but may not work if the hole is microscopic or located in a hard-to-reach place, for example, inside a foam layer.
For more accurate diagnostics, professionals use leak detectors (helium or halogen). The helium method is considered the “gold standard”: a small amount of helium is added to the system, and the probe of the device is moved along the contour. The device reacts to the presence of helium with a sound signal, allowing you to find a leak with an accuracy of a millimeter.
⚠️ Attention: When searching for leaks in a foamed circuit (evaporator inside the cabinet), a soap solution will not help. If the pressure drops and there are no external holes, it means that the pipeline has rotted inside the insulation. In this case, the installation of an external evaporator is required.
Sometimes a leak can be detected by a characteristic whistle if the depressurization is significant. However, you should not rely only on hearing, since many microcracks do not make sounds.
Analysis of pressure drop and diagnostics
After carrying out a visual inspection and applying the solution, it is necessary to leave the refrigerator under pressure for a certain time for monitoring. This is called control exposure. The duration of exposure depends on the size of the system and the required accuracy, but for household refrigerators 6-12 hours are usually sufficient.
If during this time the pressure gauge needle remains in place, the system can be considered sealed. If the pressure drops even by 0.5 atmospheres, it means there is a leak. It is important to take into account the temperature coefficient: when the air temperature in the room changes, the gas pressure also changes.
- 🌡️ When the temperature in the room increases, the pressure in the circuit will increase.
- 🌡️ When the temperature drops (for example, at night), the pressure will drop.
- 🌡️ For accurate calculations, use the law Gay-Lussac or tables of pressure versus temperature.
To eliminate the influence of temperature, leave the pressure gauge in a room with a constant temperature or use compensated pressure gauges. If temperature changes are significant, adjust the readings before drawing conclusions about the presence of a leak.
☑️ Pressure test checklist
Evacuation after crimping
Once the tightness has been confirmed and all leaks have been eliminated, it is necessary to remove nitrogen from the system. However, simply releasing the gas is not enough. Before charging with refrigerant, the system must undergo a procedure evacuation.
The vacuum pump is connected to the service port, and all air and residual nitrogen are pumped out of the circuit. The goal of the process is to reduce the pressure in the system to minimum values (usually 200-500 microns) in order to remove moisture that may be present in the tubes in the form of steam.
Moisture in the system is the main enemy. When the refrigerator operates, water freezes in the capillary tube, forming an ice plug that blocks the circulation of freon. In addition, water reacts with oil and refrigerant, forming acid, which corrodes the compressor windings from the inside.
Evacuation time:- Minimum: 15-20 minutes
- Optimal: 30-40 minutes
- For systems with compressor replacement: 1 hour
After pumping is complete, close the pressure gauge valve, turn off the pump and leave the system for 15-20 minutes. If the pressure gauge needle does not rise, it means that the vacuum is maintained and the system is ready to be charged with refrigerant.
What will happen if you do not make a vacuum?
Residual air and moisture will lead to increased condensation pressure, overheating of the compressor and eventual failure. An ice plug can form after several hours or days of work.
Common mistakes when crimping
Beginners often make mistakes that negate all the work. The most common of them is using a car compressor or pumping the system by eye. The pressure of 2-3 atmospheres that the compressor creates is not enough to identify microcracks through which freon will escape in a few weeks.
Another mistake is ignoring the replacement of the filter-drier. When the system is opened for pressure testing, moisture from the air enters the filter. If you leave the old filter, it will not be able to effectively dry the refrigerant, which will lead to problems in the future.
It is also dangerous to exceed the allowable pressure. The aluminum tubes of modern evaporators are very thin and can burst at pressures above 15-18 atmospheres. Always check the technical specifications of the specific unit.
⚠️ Attention: Specifications and permissible pressures may vary depending on the model and year of manufacture of the refrigerator. Always check the information on the device nameplate or in the manufacturer’s official documentation before starting work.
Careful adherence to crimping technology is the key to long-lasting repairs. Do not save time at this stage, since re-disassembling the refrigerator to find a missed leak will take much more effort and money.
FAQ: Frequently asked questions
Is it possible to perform pressure testing with a conventional air compressor?
Technically, it is possible to create pressure, but this is ineffective. The compressor produces a maximum of 6-8 atmospheres, which is not enough to detect minor leaks. In addition, the air contains moisture, which will ruin the system from the inside. Use only dry nitrogen.
How long should the refrigerator hold pressure?
The minimum time for a quality check is 6 hours. During this time, even a slow drop in pressure becomes visible. Professionals often leave the system under pressure for 24 hours for a 100% guarantee.
Why does the pressure drop, but there are no bubbles?
This means that the leak is in a hidden place, most likely in the foamed evaporator inside the refrigerator body. It is impossible to find it visually; it requires opening the thermal insulation or installing an external evaporator.
Is it necessary to change the oil in the compressor after pressure testing?
If pressure testing was carried out with dry nitrogen and the system was not open for a long time, it is not necessary to change the oil. But if moisture or dirt got into the system, or the compressor was operating in air, the oil must be replaced.