Mitsubishi Electric PUZ-WZ50VAA Service Manual page 9

The appliance shall be installed in accordance with national wiring regulations.
The terminal block cover panel of the outdoor unit must be firmly attached. If the cover panel is mounted incorrectly and
dust and moisture enter the unit, electric shock or fire may result.
(5) Detection of Flammable Refrigerants
Under no circumstances shall potential sources of ignition be used in the 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 equip-
ment shall be set at a percentage of the LFL of the refrigerant and shall be calibrated to the refrigerant 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 refrigerant shall be recovered from the system.
For appliances containing flammable refrigerants, oxygen free nitrogen (OFN) shall then be purged through the system
both before and during the brazing process.
(7) Removal and Evacuation of the R290 refrigerant
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 considera-
tion. The following procedure shall be adhered to:
• remove refrigerant
• purge the circuit with inert gas for 5 min
• evacuate down the refrigerant circuit to a pressure of 30 kPa absolute or lower
• purge again with inert gas for 5 min
• open the circuit by cutting, not by flame
Do not remove the parts from the unit by flame such as brazing and by tools such as a hacksaw or mechanical cutting
tools which can cause sparking.
The refrigerant charge shall be recovered into the correct recovery cylinders. For appliances containing flammable refrig-
erants, 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.
Be sure to use a vacuum pump and a recovery machine compliant with R290 that has been specially designed and test-
ed not to be an ignition source of itself. It is deeply better to use the recovery machine that comply with explosion-proof
standards such as ATEX and IECEx.
(8) Recovery
When removing refrigerant from a system, either for servicing or decommissioning, it is recommended good practice that
all refrigerants are removed 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 refrigerant and labelled for that refrigerant (i.e. spe-
cial cylinders for the recovery of refrigerant). Cylinders shall be complete with pressure-relief valve and associated shut-
off valves in good working order. Empty recovery cylinders are evacuated and, if possible, cooled before recovery
occurs.
The recovery equipment shall be in good working order with a set of instructions concerning the equipment that is at
hand and shall be suitable for the recovery of all appropriate refrigerants including, when applicable, flammable refriger-
ants. In addition, a set of calibrated weighing scales shall be available and in good working order. Hoses shall be com-
plete 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 arranged. Do not mix refrigerants in recovery units and especially not in cylinders. 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 evacuation 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 pro-
cess. When oil is drained from a system, it shall be carried out safely.
OCH816
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