Mitsubishi Electric City Multi PEFY-M20VMA-A Technical & Service Manual page 4

searching for or detection of refrigerant leaks.
A halide torch (or any other detector using a naked flame) shall not be
used.
(6) Leak Detection Methods
Electronic leak detectors may be used to detect refrigerant leaks but, in
the case of flammable refrigerants, the sensitivity may not be adequate,
or may need re-calibration. (Detection equipment shall be calibrated in a
refrigerant-free area.)
Ensure that the detector is not a potential source of ignition and is suitable
for the refrigerant used. Leak detection equipment shall be set at a per-
centage of the LFL of the refrigerant and shall be calibrated to the refrig-
erant employed, and the appropriate percentage of gas (25% maximum)
is confirmed.
Leak detection fluids are suitable for use with most refrigerants but the
use of detergents containing chlorine shall be avoided as the chlorine may
react with the refrigerant and corrode the copper pipe-work.
If a leak is suspected, all naked flames shall be removed/extinguished.
If a leakage of refrigerant is found which requires brazing, all of the refrig-
erant shall be recovered from the system, or isolated (by means of shut off
valves) in a part of the system remote from the leak. For appliances con-
taining flammable refrigerants, oxygen free nitrogen (OFN) shall then be
purged through the system both before and during the brazing process.
(7) Removal and Evacuation
When breaking into the refrigerant circuit to make repairs – or for any other
purpose conventional procedures shall be used. However, for flammable
refrigerants it is important that best practice is followed since flammability
is a consideration. The following procedure shall be adhered to:
• remove refrigerant
• purge the circuit with inert gas
• evacuate
• purge again with inert gas
• open the circuit by cutting or brazing.
The refrigerant charge shall be recovered into the correct recovery cylin-
ders. For appliances containing flammable refrigerants, the system shall
be "flushed" with OFN to render the unit safe. This process may need to
be repeated several times.
Compressed air or oxygen shall not be used for purging refrigerant systems.
For appliances containing flammable refrigerants, flushing shall be
achieved by breaking the vacuum in the system with OFN and continuing
to fill until the working pressure is achieved, then venting to atmosphere,
and finally pulling down to a vacuum. This process shall be repeated until
no refrigerant is within the system. When the final OFN charge is used,
the system shall be vented down to atmospheric pressure to enable work
to take place. This operation is absolutely vital if brazing operations on the
pipe-work are to take place.
Ensure that the outlet for the vacuum pump is not close to any ignition
sources and that ventilation is available.
(8) Charging Procedures
In addition to conventional charging procedures, the following require-
ments shall be followed:
• Ensure that contamination of different refrigerants does not occur
when using charging equipment. Hoses or lines shall be as short as
possible to minimize the amount of refrigerant contained in them.
• Cylinders shall be kept upright.
• Ensure that the refrigeration system is earthed prior to charging the
system with refrigerant.
• Label the system when charging is complete (if not already).
• Extreme care shall be taken not to overfill the refrigeration system.
Prior to recharging the system, it shall be pressure-tested with the appro-
priate purging gas. The system shall be leak-tested on completion of
charging but prior to commissioning. A follow up leak test shall be carried
out prior to leaving the site.
(9) Decommissioning
Before carrying out this procedure, it is essential that the technician is
completely familiar with the equipment and all its detail. It is recommend-
ed good practice that all refrigerants are recovered safely. Prior to the task
being carried out, an oil and refrigerant sample shall be taken in case
analysis is required prior to re-use of reclaimed refrigerant. It is essential
that electrical power is available before the task is commenced.
a) Become familiar with the equipment and its operation.
b) Isolate system electrically.
c) Before attempting the procedure, ensure that:
• mechanical handling equipment is available, if required, for handling
refrigerant cylinders;
• all personal protective equipment is available and being used correct-
ly;
• the recovery process is supervised at all times by a competent person;
• recovery equipment and cylinders conform to the appropriate stan-
dards.
d) Pump down refrigerant system, if possible.
e) If a vacuum is not possible, make a manifold so that refrigerant can be
removed from various parts of the system.
HWE19070
f) Make sure that cylinder is situated on the scales before recovery takes
place.
g) Start the recovery machine and operate in accordance with manufac-
turer's instructions.
h) Do not overfill cylinders. (No more than 80 % volume liquid charge).
i) Do not exceed the maximum working pressure of the cylinder, even
temporarily.
j) When the cylinders have been filled correctly and the process complet-
ed, make sure that the cylinders and the equipment are removed from
site promptly and all isolation valves on the equipment are closed off.
k) Recovered refrigerant shall not be charged into another refrigeration
system unless it has been cleaned and checked.
(10) Labelling
Equipment shall be labelled stating that it has been de-commissioned and
emptied of refrigerant. The label shall be dated and signed. For applianc-
es containing flammable refrigerants, ensure that there are labels on the
equipment stating the equipment contains flammable refrigerant.
(11) Recovery
When removing refrigerant from a system, either for servicing or decom-
missioning, it is recommended good practice that all refrigerants are re-
moved safely. When transferring refrigerant into cylinders, ensure that
only appropriate refrigerant recovery cylinders are employed. Ensure that
the correct number of cylinders for holding the total system charge are
available. All cylinders to be used are designated for the recovered refrig-
erant and labelled for that refrigerant (i.e. special cylinders for the recov-
ery of refrigerant). Cylinders shall be complete with pressure-relief valve
and associated shut-off valves in good working order. Empty recovery cyl-
inders are evacuated and, if possible, cooled before recovery occurs.
The recovery equipment shall be in good working order with a set of in-
structions concerning the equipment that is at hand and shall be suitable
for the recovery of all appropriate refrigerants including, when applicable,
flammable refrigerants. In addition, a set of calibrated weighing scales
shall be available and in good working order. Hoses shall be complete
with leak-free disconnect couplings and in good condition. Before using
the recovery machine, check that it is in satisfactory working order, has
been properly maintained and that any associated electrical components
are sealed to prevent ignition in the event of a refrigerant release. Consult
manufacturer if in doubt.
The recovered refrigerant shall be returned to the refrigerant supplier in
the correct recovery cylinder, and the relevant waste transfer note ar-
ranged. Do not mix refrigerants in recovery units and especially not in cyl-
inders. If compressors or compressor oils are to be removed, ensure that
they have been evacuated to an acceptable level to make certain that
flammable refrigerant does not remain within the lubricant. The evacua-
tion process shall be carried out prior to returning the compressor to the
suppliers. Only electric heating to the compressor body shall be employed
to accelerate this process. When oil is drained from a system, it shall be
carried out safely.
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