The most obvious outward sign of a leak is a refrigerant pressure gauge reading of zero. When a refrigerant leak occurs, the first step is to locate the specific leak point; this process requires patience, meticulousness, and a specific methodology. The procedure is as follows: First, perform a visual inspection by opening the machine's access panels to observe the interior. Since the refrigerant circulating during operation is mixed with compressor lubricating oil, any escaping refrigerant will carry some of this oil out with it. Therefore, carefully examine the machine's interior; if you observe streaks or patches of oily residue, that area is very likely the location of the leak. Next, inspect the capillary copper tubes inside the machine-specifically the thin copper tubing (under 6 mm in diameter) and the process tubes-to check for any signs of breakage. After completing these basic checks, mark any areas that appear suspicious. The next step is to confirm the exact leak point by pressurizing the system with an inert gas. Ideally, nitrogen should be used to pressurize the system; if nitrogen is unavailable, gaseous refrigerant can serve as a substitute. However, it is strictly forbidden to use oxygen for leak testing under pressure-doing so is extremely dangerous and could be fatal.
When pressurizing the system, begin by introducing the gas slowly while simultaneously monitoring the pressure gauge on the refrigerated air dryer (smaller units typically feature only a low-pressure gauge, while units of 15 cubic meters or larger are equipped with both high- and low-pressure gauges). Temporarily halt the pressurization once the pressure reaches approximately 0.2 MPa (2.0 kgf). Then, listen carefully for any audible hissing sounds indicating a gas leak within the machine; if a sound is detected, you can pinpoint the leak location by tracing the source of the noise. If no sound is heard, continue increasing the pressure to between 0.4 and 0.5 MPa. At this stage, take a sponge dipped in soapy water and apply it first to the areas previously identified as suspicious, and then to all connecting joints and tubing (specifically the copper flare nuts) throughout the machine's interior. If a leak is present, bubbles will form and blow outward from the leak point; this step requires extreme care and attention to detail. If, after utilizing the methods described above, you are still unable to locate the leak, then-unfortunately-it is highly probable that the leak is internal to the evaporator. Internal evaporator leaks are generally more difficult to resolve. First, the leak must be definitively confirmed; this can be achieved by isolating the evaporator from the rest of the refrigeration system and pressurizing it independently. If the pressure within the isolated evaporator drops over time, an internal leak is confirmed. Another relatively simple method involves opening the compressed air inlet. If the refrigerant pressure gauge shows a rise in pressure after a period of time, it confirms that the refrigeration system has established a connection with the air system-as the evaporator serves as the sole point of exchange between the two. Consequently, this confirms the presence of an internal leak within the evaporator.
Once the leak point has been identified, the next step is to repair it. Depending on the nature of the leak, different approaches are required: for issues such as a loose flared connection, a simple tightening with a wrench is sufficient; however, for leaks involving copper tubing welds, brazing is necessary. Brazing is one of the most common techniques in the refrigeration repair industry. Essentially, it involves using an oxygen-acetylene flame to heat a low-silver brazing rod and the specific area requiring repair, allowing the rod and the repair site to fuse together and effectively seal the leak. When brazing, the pressure within the refrigeration system must first be completely vented to zero. Then, using a brazing torch, the acetylene valve is opened first and ignited; oxygen is subsequently introduced and adjusted slowly to achieve a neutral-to-oxidizing flame. Finally, the area to be welded and the silver brazing rod are heated until they fuse together. Mastering the specific techniques involved requires the operator to undergo appropriate training. After the leak point has been repaired, the system must be pressurized again to verify that the brazing repair was successful.
Upon completion of the leak repair, the system must be evacuated (vacuumed) before adding the specified mass of liquid refrigerant (refer to the basic configuration table for the exact quantity). Refrigerant should be charged into the system via the dedicated liquid-charging needle valve provided on the refrigerated air dryer. For larger machines, the initial refrigerant charge should be introduced through the high-pressure charging port; if the full specified dosage cannot be added in a single charge, the remaining amount should be slowly added through the low-pressure port after the machine has been started up.