33
GB
equipment must be set at a percentage of the LFL of the refrigerant and must be calibrated
to the refrigerant used, and the appropriate percentage of gas (25% maximum) must be
confirmed. Leak detection fluids are suitable for use with most refrigerants, but detergents
containing chlorine must be avoided as the chlorine may react with the refrigerant and
corrode the copper pipework. All naked flames must be removed/extinguished if a leak is
suspected. If a refrigerant leak is found that requires brazing, all the refrigerant must be
recovered from the system or isolated (by means of shut-off valves) in a part of the system
not affected by the leak. Oxygen-free nitrogen (OFN) must then be passed through the
system both before and during the brazing process.
• Removal and evacuation
Conventional procedures must be used when accessing the refrigerant circuit for repairs
or any other purpose. However, it is important to ensure that best practice is followed as
flammability must be considered. The following procedure must be adhered to:
Remove the refrigerant;
Purge the circuit with inert gas;
Evacuate the circuit;
Purge again with inert gas;
Open the circuit by means of cutting or brazing.
The refrigerant charge must be recovered to the correct recovery cylinders. The system must
be flushed with OFN to render the unit safe. This process may need to be repeated several
times. Compressed air or oxygen must not be used for this task.
Flushing must be take place by breaking the vacuum in the system using OFN and
continuing to fill until the working pressure is achieved, then venting to the atmosphere, and
finally reducing the pressure to a vacuum pressure. This process must be repeated until there
is no refrigerant left in the system. When the final OFN charge is used, the system must be
vented to atmospheric pressure to enable work to take place. This operation is absolutely
vital if brazing operations are to take place on the pipework.
Ensure that the socket for the vacuum pump is not close to any ignition sources and that
ventilation is available.
• Charging procedures
Besides conventional charging procedures, the following requirements must be met. Ensure
that there is no contamination of different refrigerants when using charging equipment.
Hoses or lines must be as short as possible so as to minimise the amount of refrigerant inside
them. Cylinders must be kept upright.
Ensure that the refrigeration system is earthed prior to charging the system with refrigerant.
Label the system when charging is complete (unless it is already labelled).
Extreme care must be taken not to overfill the refrigeration system.
The system must be pressure-tested using OFN prior to recharging. The system must be
tested for leaks on completion of charging but prior to commissioning. A follow-up leak test
must be carried out prior to leaving the site.
• Decommissioning
Before carrying out this procedure, it is essential for the technician to be completely familiar
with the equipment and all its details. Ensuring that all refrigerants are recovered safely is
recommended good practice. Prior to the task being carried out, oil and refrigerant samples
must be taken in case analysis is required prior to reuse of reclaimed refrigerant. It is
essential to ensure that electricity is available before starting the task.
a) Familiarise yourself with the equipment and its operation.
b) Isolate the system electrically.
