www . refrigerationandaircon . co . za RACA Journal I August 2023 41
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• For 134A , R600a and R290 used in domestic applications with pressed aluminium , evaporators between 600 and 800 kPa is recommended .
• For R134a systems and other refrigerants which have similar working pressures the recommended test pressure is 1 050 to 1 400 kPa .
• For R 22 systems and other refrigerants which have similar working pressures the recommended pressure is 1 750 to 2 100 kPa .
• For R410a , 3 800 kPa is recommended .
When pressurising the system , the pressure must be increased in stages with a comprehensive leak test between each stage and the pressure only increased when no leaks are found . The nameplate on some systems indicates the recommended test pressure ; in this case this is the pressure to be applied . After the test pressure has been reached the most suitable leak detection procedure can be applied .
THE OIL SPOT METHOD This is an observation of the system rather than an actual leak detection method .
Together with the refrigerant , oil is circulating through the system . If the refrigerant leaks out there is usually an amount of oil leaking out with it . As there is always air ( with dust ) flowing over the plant the areas where there is leakage will be oily and dusty . Thus , to find the leaks look for these spots .
THE SOAP BUBBLE METHOD This method is probably the simplest and safest method of leak testing and can even be used by inexperienced persons , because all the materials used are non-toxic and non-explosive . The disadvantage of the method is that small leaks are difficult to detect , and the testing can take a long time . Also , in some instances you cannot easily access the joints to be tested .
For this method , a strong water-soap solution is ‘ painted ’ on all areas suspected of leaking ; areas such as joints , gaskets , seals , fittings , and welds . Where there is a leak , the solution will cause bubbles . Specially made solutions are available from refrigeration suppliers .
There are some that feel that this method is not accurate enough to detect very small leaks but in general the method is cheap and easily applied . It may be advisable to use this method in conjunction with an electronic leak detector .
ELECTRONIC LEAK TESTING The electronic leak detector is the most sensitive of the commonly available leak testing instruments and is available for hydrocarbons . Note : It is important to ensure that the electronic tester is suitable for the type of refrigerant utilised by the system being tested .
Supplied by ACRA
Electronic leak detector
I often hear the complaint that these types of leak detection devices do not really work as they are too sensitive . Some older electronic detectors were so sensitive that they could not be used if there was refrigerant gas present in the general atmosphere around the plant . The more modern detectors have a button which , when pressed , cancels out the concentration in the general atmosphere and will only react when the sample contains more gas than the atmosphere . This is the preferred method for detecting all leaks and in particular very small leaks . A disadvantage is that fans can disperse leaking refrigerant making a leak hard to locate utilising this method alone .
ULTRAVIOLET LEAK DETECTION With the ultraviolet leak detection method , a small amount of fluorescent dye is added to the oil in the compressor and is typical to automotive systems . This method can be used in all systems where there is oil circulating through the system with the refrigerant . If a leak occurs anywhere in the system the refrigerant , together with the oil and the fluorescent dye , will leak out . Leak finding is done with an ultraviolet light . When this light is shone onto the plant the fluorescent dye will show up as a bright greenyellow or pink , fluorescent glow . Very small leaks can be found with this method .
Because it is so easy and fast , this method can be used as a routine method . If the plant is in a dark surrounding it does not even have to be switched off as it is easy to see the fluorescent glow in these circumstances . The dye can be added directly to the oil , or it can be added into the suction side of the compressor with the aid of
a special mist infuser . After the dye has been added the plant must be run for some time in order to give the dye a chance to leak out - if there is a leak .
Large leaks will become apparent in a matter of hours ; small leaks take much longer to locate . The fluorescent dye stays in the system until the oil is changed , even if all the refrigerant escapes or the system is evacuated .
Note : Some manufacturers do not guarantee compressors if dye is added . Having said that , most automotive manufacturers add dye to the air conditioning systems to facilitate leak detection .
ULTRASONIC LEAK TESTING Ultrasonic leak detectors operate on a completely different principle from all the other methods . This detector detects and
www . refrigerationandaircon . co . za RACA Journal I August 2023 41