The refrigeration circuit is closed; the refrigerant is not consumed, and if it has gone down it has leaked. A leak is both expensive and harmful: capacity falls, the compressor runs hot, consumption rises and greenhouse gas enters the atmosphere. A leak test is carried out in two situations: a newly installed or repaired circuit is tested with nitrogen before refrigerant is charged, and a running system is scanned at set intervals. The first proves tightness, the second catches leaks that develop over time. Even a small leak takes away a significant part of the charge by the end of the year.
The methods complement one another. An electronic detector can sense leaks of the order of 5 grams a year; the probe is moved slowly beneath the joints, because the refrigerant is heavier than air. Foam or soapy water pinpoints the location of the leak with bubbles at the suspect spot. An oil stain is mostly the first visible sign of a leak. Ultraviolet dye and a nitrogen–hydrogen tracer gas mixture are used for leaks that are hard to find. A vacuum that holds is not regarded as sufficient proof by itself. The sensor of the detector must be calibrated at regular intervals.
The mandatory frequency of checks depends on the CO₂ equivalent of the charge: at least once a year at 5 tonnes and above, every six months above 50 tonnes, every three months above 500 tonnes. The equivalent is the charge quantity multiplied by the GWP; a charge of 1.3 kg with R404A or 3.6 kg with R449A exceeds the 5 tonne threshold. The checks are carried out by a certified technician and recorded together with the date, the findings and the quantity of gas added. A leak that is found is repaired and checked again after the repair.
The places where leaks most often occur are well known: flare connections, service valves and Schrader cores, pressure switch capillary tubes, the brazed joints of vibrating pipes, compressor shaft seals, evaporator return bends. Adding gas without finding the leak does not solve the problem; the same gas is charged again a few months later. In zeotropic blends a large leak also upsets the composition. When working out the threshold for your own system you can use the GWP values in our refrigerant pressure–temperature chart. Using brazed joints instead of flare connections permanently reduces the risk of leaks.