Mitsubishi Electric CAHV-R450YA-HPB Service Manual page 22

[ I Read Before Servicing ]
8. Cabling
Check that cabling will not be subject to wear, corrosion, excessive pressure, vibration, sharp edges or any other adverse
environmental effects. The check shall also take into account the effects of aging or continual vibration from sources such
as compressors or fans.
9. Refrigerant leakage detection
The following leak detection methods are deemed acceptable for all refrigerant systems.
1) Electronic leak detectors may be used to detect refrigerant leaks but, in the case of slightly 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.
2) If a leak is suspected, all naked flames shall be removed/extinguished.
3) If a leakage of refrigerant is found which requires brazing, all of the refrigerant shall be recovered from the system, or isolated
(by means of shut off valves) in a part of the system remote from the leak. Because R454C is slightly flammable, oxygen free
nitrogen (OFN) shall be poured through the system both before and during the brazing process to purge R454C.
10. Refrigerant removal and vacuum drying for service
1) R454C is slightly flammable. Follow the procedures below to reduce the risk of R454C from catching fire:
1. Remove refrigerant;
2. Purge the circuit with inert gas;
3. Evacuate;
4. Purge again with inert gas;
5. Open the circuit by cutting or brazing.
2) The charged refrigerant shall be recovered into the recovery cylinders designated for use with R454C. For appliances containing
slightly 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.
3) Because R454C is slightly flammable, 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
pipework are to take place.
4) Ensure that the outlet for the vacuum pump is not close to any ignition sources and that ventilation is available.
11. Charging Procedures
1) In addition to conventional charging procedures, the following requirements 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.
2) Prior to recharging the system, it shall be pressure-tested with the appropriate 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.
12. Decommissioning
1) Before carrying out this procedure, it is essential that the technician is completely familiar with the equipment and all its detail.
It is recommended 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.
2) Become familiar with the equipment and its operation.
3) Isolate system electrically.
4) 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 correctly;
• the recovery process is supervised at all times by a competent person;
• recovery equipment and cylinders conform to the appropriate standards.
HWE22020
- 13 -
GB