Leak Detection Methods and Techniques for Air Conditioning Systems

At midsummer, the maintenance of automobile air conditioners entered the busy season, and various kinds of maintenance on air conditioning system failures are gradually increasing. In the common failures of air-conditioning systems, leakage line inspections and repairs have caused headaches for first-line service technicians. As it is time consuming and laborious to check the leakage point of the air conditioning system, if there is no good method, it will not only greatly affect the work efficiency of the maintenance, but will also lead to a significant decrease in customer satisfaction.

In my daily work, I found that most of the frontline technicians used a fluorometer (assembly of high and low pressure two headers) (Figure 1) to conduct tests when conducting empty survey leaks: high-pressure pipe access system, low pressure Methods that do not connect to the system, or that use high and low pressure tubes to access the system but exert less pressure. After pressurizing with nitrogen, holding pressure for 1 h or more indicates that the system does not leak. However, there are cases where watch dropout occurs (because there are expansion valves, compressors and other bulky components in the air-conditioning system piping, the pointer indicates a sharp drop in pressure value), and slow helium is produced. This kind of watch drop is a false leak. A little longer will not happen again. The disadvantage of this method is that it is not accurate enough, it takes a long time, and customers often complain about waiting too long. In order to solve this problem, the author himself summarized some air conditioning leak detection tips and recommended it to everyone, hoping to help everyone solve this problem.

1. Improvement of normal nitrogen pressure leak detection method

Before checking leaks, first modify the fluorine meter: remove the low pressure header, and then use a high pressure meter instead of the low pressure meter. Such a fluorine meter is equipped with two high-voltage headers (Figure 2). The reason for the modification is that, according to the conventional method, the use of a low-pressure gauge for pressure leak detection often results in damage to the low-voltage gauge. (At present, most pressure detection methods recommend an inflation pressure of about 0.78 MPa, which is exactly the maximum range of the low-voltage gauge.) After changing the pressure gauge to two high-pressure gauges, the author not only improves the efficiency and convenience of leak detection pressure detection, but also does not damage the fluorine meter.

When checking leaks, connect the two headers to the connectors of the high and low pressure pipelines, respectively, and pressurize them with nitrogen (Figure 3). The pressure should be added between 2.0 and 2.5 MPa (Fig. 4) because the air-conditioning fan generally produces a pressure between 1.7 and 2.0 MPa when it is rotating at a high speed. This means that the air conditioner will often work under this pressure condition. Leaks will also occur. This happens. The pressure resistance range of air-conditioning systems designed for most models is generally not less than 3.0 MPa, that is, there is no damage to the system within this pressure range. However, in actual maintenance, we should also consider the problem of system aging. The author summarizes this relative safety in practice. And fast and practical nitrogen pressure range.

Under this pressure (2.0~2.5 MPa), if the air-conditioning system can maintain the pressure for 20 minutes (there is no indication of the meter dropping, the indicator should not change), the system can be basically judged as no leakage (but it should be noted that the compressor Is a working part). Because the pressure at both the high pressure and low pressure is consistent at this time, the indications on both sides should be the same and constant. However, this leak detection method is inapplicable to the leakage that occurs when the compressor pump head is in operation (it is not possible to use static pressure leak detection when the fault is not serious). Compared with the general fluorine meter leak detection method, the biggest advantage of this method is that it does not damage the fluorine meter (low pressure meter) and the measurement is accurate and fast.
With the continuous development of science and technology, many advanced equipments for the detection and maintenance of automotive air conditioners are available. Nowadays, many automotive air conditioning refrigerant recovery charging devices also have air-conditioning system leak detection capabilities. However, for various reasons, this kind of equipment has not yet been popularized in many integrated maintenance companies. In these maintenance companies lacking professional equipment, the above-mentioned leak detection methods may be able to alleviate the urgent situation, but in the end it will be replaced by more professional and standardized testing equipment.

2. How to determine the location of the leak

(1) Pressurized bubble leak detection method: While using the nitrogen pressure leak detection method, use the aqueous detergent foam to smear the air conditioning system piping and the appearance of various components (we recommend using a sponge for smearing to maximize the amount of foam). Check for bubbles. The reason why it is recommended to use detergent is that it has a fine and long-lasting foam that is far superior to soapy water and other foaming solutions. When in use, the compressor head can be coated and covered. When the system pressure is 2.0~2.5 MPa, shake up and down and increase the frequency of shaking as much as possible to check whether there is any leakage at the pump head. The author has used this method to find too many such leaks. Such a leak detection method is simple, easy, and low cost, suitable for daily air conditioning system leak inspection.

(2) Fluorescence Tracer Leak Detection Method (Figure 5): The principle of using a fluorescent agent to emit yellow-green fluorescence under the leak detector lamp, the fluorescent agent is added to the air-conditioning system at a certain ratio, and the system is put into use after 2 hours of operation. Spectacles, exposed to the outside of the system with a leak detector, will show bright yellow fluorescence. This leak detection cost is high, but it is very professional and accurate. A very slight amount of leakage can be found. Nowadays, 4S shops generally adopt this method.

However, the fluorescence leak detection method has certain disadvantages: the fluorescence method must be filled with the fluorescent leak detection agent into the refrigerant of the system to be inspected, and the leakage lamp and the source thereof can only be detected after the co-dissolve operation for at least 2 hours. Leakage point, if the leakage is slower, it is suggested that the owner should use it for a period of time. When the air-conditioner shows a missing refrigerant again, it will return to the factory to detect the leakage point. If a leakage point is found, the air-conditioning system components must be disassembled and removed. Then the original leakage is added to the system. The fluorescers and refrigerants are also wasted part of the waste of materials will make serious. In addition, when using the fluorescence method for leak detection, it is difficult for the system circulation pressure to reach the operating pressure under real working conditions (high temperature and high pressure). According to the author's maintenance experience, sometimes the system leakage will only appear under higher pressure, so in the case of leak detection, these invisible leakage points are often missed.

(3) Electronic Leak Detector Leak Detection (Figure 6): Use a dedicated instrument probe to move around all possible leaks (not too fast). When the leak detection device gives an alarm, it means there is a leak. Due to the rapid volatilization of the refrigerant, this method is better for use in small spaces, such as evaporators. Air-conditioning fans recommend using low gear speeds. However, instrument probes can be affected by unfavorable factors such as moisture, oil, and sometimes false positives, so pay attention to the use of techniques.

As long as these three methods are applied in a cross-cutting, flexible, and timely manner, it is believed that the leak detection of the air-conditioning system will be changed once and for all time and effortlessly, and it will be simple and easy, thus bringing convenience to front-line maintenance personnel.

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