Patent Publication Number: US-2009229295-A1

Title: Leakage test in an air conditioner

Description:
The invention relates to a method for servicing an air conditioner, particularly an automobile air conditioner, in which a test gas is applied, at a defined pressure, to the cooling circuit of the air conditioner, which has been emptied of refrigerant, within the framework of a seal test, and changes in this pressure over a time interval are recorded and analyzed. 
     During servicing of automobile air conditioners, so-called air conditioner service devices are used. These allow extensively automated servicing, after they have been connected to the air conditioner. Servicing of the air conditioner always includes a seal test, since automobile air conditioners frequently develop leaks. Leakage of the cooling circuit allows refrigerant to escape, and this harms the environment, directly and indirectly—due to the increased energy consumption. 
     An important aspect in air conditioner service devices is the degree of automation of the processes. In an ideal case, these devices work completely automatically after they have been connected, allowing efficient workshop operation. With regard to searching for leaks, vacuum tests, pressure tests with nitrogen, and filling in UV leak search additives are used as part of automated folding processes. 
     In a vacuum test, a vacuum is produced in the cooling circuit of the automobile air conditioner, by means of a vacuum pump. Subsequently, it is observed whether or not the partial vacuum within the cooling circuit drops beyond a permissible measure, which indicates a leak, due to ambient air flowing in. 
     This method of seal testing is extremely imprecise. Only very large leaks are recognized. Localization of the leak is not possible without filling the system with an additional leak search medium—such as the UV search additive described below. 
     A better method for carrying out a seal test is a pressure test with nitrogen. Here, the air conditioner is not evacuated, but rather has nitrogen applied to it. Subsequently, changes in this pressure over a time interval are recorded and analyzed. If the pressure drops below a permissible measure, this indicates a leak, which then has to be further localized, in order to plug it up. 
     Leak search sprays that are sprayed onto the cooling circuit are used for localization. At leakage sites, the leak search spray develops bubbles, like in the case of a leaking bicycle tire tube that is immersed into a bucket of water. The disadvantage of a leak search using leak search sprays consists in that here again, only extremely large leaks can be made visible. While it is true that the air conditioner service device indicates the existence of a leak, localization takes place manually. If the leak site cannot be found with leak search spray, the nitrogen has to be drained from the system, and a more precise leak search method has to be used. For the workshop, this means a great time loss and thus a high cost expenditure. 
     For precise localization of a leak site, the leak search is conducted using UV leak search additives. For this purpose, a fluid that fluoresces under ultraviolet light is filled into the automobile air conditioner. Subsequently, the cooling circuit is illuminated with a UV lamp that makes the leak sites visible. A method for filling a UV leak search additive into the cooling circuit of an air conditioner is described in DE 10 2006 036 697 A1 of the same applicant. 
     The disadvantage of a leak search using UV leak search additives consists in that these additives must first be distributed in the air conditioner, in order to ensure that it actually reaches the leak. For this purpose, the air conditioner must be in operation for an extended period of time. Furthermore, the fluorescent agents are hazardous to the environment. 
    
    
     Proceeding from the state of the art as described above, and, in particular, from the method for a pressure test using nitrogen, the task of the present invention consists in indicating a method for a seal test that has a high degree of automation, can be carried out as rapidly as possible, and is less hazardous for the environment. 
     This task is accomplished in that a gas mixture of nitrogen and hydrogen is used as the test gas, and that the cooling circuit is searched with a hydrogen sensor after a pressure drop has been recorded. 
     The present method continues to use the proven method of an elevated pressure seal test using nitrogen. The observation of the pressure change over a time interval, after the nitrogen is filled in, can be completely automated. The basic idea of the present invention, however, consists in modifying the test gas that is adjusted, in such a manner that it is suitable, at the same time, for localization of a leak that might be detected. For this purpose, hydrogen is mixed in with the nitrogen, and this can be detected using a hydrogen sensor, with the required precision. 
     The particular advantage can be seen, first of all, in the time gain, since filling a leak search additive in separately, after a leak has been found, is eliminated. Furthermore, allowing the air conditioner to run to distribute the search additive in the cooling circuit is also eliminated, since this distribution is guaranteed by the excess pressure of the test gas mixture that is filled in. Finally, a gas mixture composed of nitrogen and hydrogen—a mixture of 95% N 2  and 5% H 2  is preferably proposed—is relatively non-hazardous, inexpensive, and environmentally neutral. The test gas can therefore be released directly into the environment after the seal test has taken place, something that must be avoided at all costs when using UV search additives. The light hydrogen rapidly penetrates through the smallest leaks, and can be easily detected with a sensor. Consequently, a proportion of 5% hydrogen in the test gas is sufficient, so that the risk of the hydrogen igniting is extremely low, and additionally is lowered by the nitrogen. 
     It should be made clear that the method according to the invention also cannot be automated completely, since localization of the leak must take place manually, using the hydrogen sensor. However, sealing of the leak takes place manually, in any case, so that searching the cooling circuit with the hydrogen sensor does not represent any significant additional effort. If the system does not have any leaks, the method remains completely automatic—aside from connecting the air conditioner service device. 
     Not only the refrigerant, but also refrigerating machine oil that is required for lubricating the compressor, circulates in the cooling circuit of an air conditioner. After the refrigerant has been drained, the refrigerating machine oil generally remains in the cooling circuit. However, it can happen that a partial amount of the refrigerating machine oil is entrained out of the cooling circuit when the test gas is drained, with the result that the required fill level is not reached. In order to avert damage to the compressor and prevent exit of the refrigerating machine oil, which is harmful to the environment, the invention proposes that entrained refrigerating machine oil be precipitated from the drained test gas, and that the amount of refrigerating machine oil that was precipitated be added to the cooling circuit again. Precipitation takes place in an oil precipitator, which must be accommodated in the air conditioner service device, in terms of construction. After the test gas has passed through the oil precipitator, it can be released into the environment. 
     It should be made clear that it is not the precipitated refrigerating machine oil itself, but only its amount, which is to be fed back into the cooling circuit. For example, in practice, it is possible to dispose of the entrained refrigerating machine oil and to introduce fresh refrigerating machine oil into the air conditioner. Just as well, however, the precipitated refrigerating machine oil can also be filled back in. Disposal of the precipitated agent is eliminated by means of this method of procedure. 
     If, however, fresh refrigerating machine oil is supposed to be filled in, it is necessary to determine the precipitated amount as refrigerating machine oil. Weighing is a possible method for this. 
     In the following, a method for servicing an air conditioner is described, which makes use not only of the seal test according to the invention, but also of the return of the refrigerating machine oil according to the invention. 
     The method is carried out using an air conditioner service device. A pressure bottle containing the test gas composed of 95% nitrogen and 5% hydrogen is connected with this device. The test gas is stored in the bottle under pressure, so that the required test pressure does not have to be produced on location. 
     The filling hoses of the air conditioner service device are then connected with the air conditioner, and the pressure regulator of the test gas bottle is set to 5 bar. The air conditioner service device now first draws the refrigerant out of the cooling circuit, and automatically fills the test gas into the air conditioner. Over a time interval, the air conditioner service device records the pressure prevailing in the system, and analyzes it. In this connection, it automatically checks whether the pressure is dropping below an impermissible measure. 
     If this is not the case, the test gas is drained by the air conditioner service device. In this connection, the refrigerating machine oil entrained by the test gas is precipitated and weighed. During the subsequent oil filling process, the corresponding amount is automatically introduced into the air conditioner again. 
     However, if the control technology registers a rapid drop in pressure, the air conditioner fails the pressure test. The air conditioner service device stops the actual servicing process, and requests the service technician to search the cooling circuit and locate the leak, using a separate hydrogen sensor that is structured as a handy, mobile test device having a long, flexible test snout. The hydrogen sensor is sufficiently sensitive so that even the smallest leaks can be found, without using an additional leak search medium. 
     After the service technician has located the leak, he confirms this on the air conditioner service device by pressing a key, and the test gas is drained from the air conditioner by way of a drain valve. 
     Here again, the refrigerating machine oil entrained by the test gas is precipitated and weighed, so that the corresponding amount can be filled in again afterwards. The air conditioner, which has now been emptied, can be repaired.