New refrigerant in old pipes

With the high-pressure refrigerant R410A increasingly being used in new air-conditioning equipment, Daikin offers guidance on the use of pipework originally installed for R22 and R407C. If the piping passes pressure tests and is in good condition, it can be used as part of an R410A system. The old system must be pumped down to return its refrigerant to the redundant outdoor unit. Running the system for about 30 minutes in cooling mode will dissolve the mineral oil in the refrigerant and circulate it. The oil will then be discharged during pumping down, leaving about 1% (which is considered acceptable as a contaminant) and thereby effective cleaning the pipe. Since Daikin uses ether oil, rather than moisture-sensitive ester oil, in its compressors, there is no need for an auxiliary activated-carbon filter to be fitted to RZQ-B7 units to remove water. If pumping down is not carried out correctly, the large quantities of mineral oil in the refrigerant system will lead to contamination, causing corrosion of brass, SUS and iron — and thus damage to the expansion valve. Existing piping must also comply with vertical separation and horizontal pipe runs for the new equipment. Further, there must be no record of previous compressor failure, since any scale adhering to the inside of the pipe can be effectively removed by pumping down. On the basis that only 1% of the original mineral oil remains after pumping down, Daikin’s use of the latest electronic expansion valves ensures that the requirement for no corrosion of the needle components will be met throughout the expected product life of 13 years.
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