On Saturday, 30 June 2018 23:27:45 UTC+1, Cynic wrote:
I've been online reading up a bit about air conditioning after seeing a neighbour having it fitted. I notice some installation manuals stress the need for the pipework to be nitrogen purged and pressure tested then a full(ish) vacuum be drawn before introducing the refrigerant. Other sources don't seem to mention this. Is a small proportion of nitrogen in the system a serious defect and what would it's effect be during operation?

They usually purge it with refrigerant gas.
Frowned on now as it is not supposed to be released to the atmosphere.