A leak test is a vital operation after the installation or service of refrigeration equipment. An efficient leak test will prevent expensive call-backs and losses.
Shortage of refrigerant in a system results in reduced plant capacity and thus in longer running times of the equipment, which could prove costly to the customer over a prolonged period. It can also be the cause of a major breakdown of a compressor due to inadequate lubrication and cooling, as explained in Chapter 10.
A system must be operating with a full charge of refrigerant to enable a commissioning engineer to obtain the design conditions by the setting of various controls (see Chapter 16).
Dye systems
Some plants may be charged at the time of installation with a refrigerant which contains a coloured dye to provide a visual indication of leakage. Systems using refrigerant containing a dye must always be liquid charged. This is most important when adding refrigerant to a system after a considerable loss due to leakage.
The dye tends to separate from the refrigerant in the cylinder and is heavier than the liquid refrigerant. Therefore it is advisable to agitate the liquid when charging or adding refrigerant by placing the cylinder in a horizontal position and rocking it gently.
Refrigerant charging procedures are dealt with in Chapter 4.
Test pressures
During normal service operations a leak test does not entail a prior evacuation of the system unless the system is contaminated or the refrigerant has been completely discharged. It is essential however, that a minimum of 30 psig (pounds per square inch gauge) or 2 bar exists in the system when testing for leaks. If no leaks are found then the system should be tested again at operating pressures.
A pressure leak test is more satisfactory and will be dealt with later.