1. Improvement of common nitrogen pressurization leak detection method
Before leak detection, modify the snow table: remove the low pressure table and replace it with the high pressure table. This snow detector is equipped with two high-voltage meters. The reason for the modification is that using the low-pressure meter to pressurize and detect leakage in the previous method often leads to the damage of the low-pressure meter. (At present, most pressure detection methods recommend that the inflation pressure is about 0.78MPa, which is exactly the widest range of the low pressure gauge. The author changed the pressure gauge into two high-pressure gauges, which not only improved the efficiency and convenience of leak detection and pressure detection, but also did not damage the snow gauge.
When detecting leakage, connect two pressure gauges to the connectors of high and low pressure pipelines respectively and pressurize them with nitrogen. The pressure should be increased to 2.0~2.5 MPa (Figure 4). Because most of the fans are running at high speed, the pressure is between 1.7~2.0MPa, and the fans often work under this pressure, and leakage will occur at this time. The design pressure range of most vehicle air conditioning systems is not less than 3.0MPa, which means that the system will not be damaged within this pressure range, but the problem of system aging should also be considered in actual maintenance. The author summarizes this safe, rapid and practical range of nitrogen pressurization.
Under this pressure (2.0~2.5MPa), if the air conditioning system can maintain this pressure for 20 minutes (there can be no symptoms, and the indicator light should remain unchanged), it can basically be judged that there is no leakage in the system (but it should be noted that the compressor is a rotating part). At this time, because the pressure of high pressure and low pressure is the same, the instructions on both sides should be similar and unchanged. However, this leak detection method does not meet the objective requirements of leakage when the compressor pump head is working and rotating (static pressure detection is powerless when this fault is not serious). Compared with most leak detection methods of snow gauge, the biggest advantage of this method is that it does not damage the snow gauge (low pressure gauge) and the measurement is accurate and fast.
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With the continuous development of science and technology, many advanced maintenance equipment for automobile air traffic regulations have been introduced. At present, many automobile air conditioning refrigerant recovery and filling equipment also has the function of air conditioning system leak detection. However, due to various reasons, this kind of equipment has not been popularized in many comprehensive repair enterprises in China. In these maintenance enterprises lacking professional equipment, the above leak detection methods may alleviate the unexpected situation, but more professional and standardized detection equipment is still needed.
2. The method of determining the location of the leak
(1) Pressurized bubble leak detection method: When using nitrogen pressurized leak detection method, use foam coating of detergent aqueous solution to adjust the appearance of system pipes and components (sponge coating is recommended to maximize the amount of bubbles), and check whether bubbles are generated. The reason for promoting the use of detergent is that its foam is fine and lasts for a long time, which is far better than foam solutions such as soapy water. When in use, the pump head of the compressor can be coated. When the system pressure is 2.0~2.5 MPa, it will shake up and down, increase the shaking frequency as much as possible, and check whether the pump head leaks. The author found too many such loopholes in this way. This leak detection method is simple and low-cost, and is suitable for leak detection of common air conditioning systems.
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(2) Fluorescent tracer leak detection method: With the aid of the principle that fluorescent agent will emit yellow-green fluorescence under the irradiation of leak detection lamp, the fluorescent agent will be added to the air conditioning system in a necessary proportion. After the system runs for 2 hours, special glasses will be put on and the outside of the system will be irradiated with the leak detection lamp, and the leak will emit bright yellow fluorescence. This kind of leak detection cost is high, but it is very professional and accurate, and a very small amount of leakage can basically be detected. At present,&; Ldquo4S & amprdquo Most stores use this method.
However, the fluorescence leak detection method has its necessary shortcomings: the refrigerant of the tested system must be filled with the fluorescence leak detector, and it will take at least 2 hours to dissolve before the leakage source and leakage point can be detected by the special lighting lamp. If the leakage is slow, it is recommended to use it with partners for a period of time. When the air is short of refrigerant, return to the factory to check the leakage point. If the leakage point is found, it must be dismantled /[/k0/ In addition, when the leakage is detected by fluorescence method, it is difficult for the circulating pressure of the system to reach the pressure under real working conditions (high temperature and high pressure). According to the author's maintenance experience, sometimes the leakage of the system only occurs under high pressure, so these unclear leakage points are often let go when leak detection.
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(3) Electronic leak detector for leak detection: use the probe of special instrument to move in all possible places (not too fast). The leak detector gives an alarm, indicating that there is a leak here. Because the refrigerant evaporates quickly, this method is very effective in small empty rooms, such as evaporators. Low speed is recommended for air conditioning. However, the instrument probe will be affected by unfavorable factors such as humidity and oil pollution, and sometimes it will cause false alarm, so it is necessary to pay attention to the use skills.
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