It's been 6 years since my Sera blew cold air ... I was sure that updating it would be very expensive and most of the advice I found was leaning towards converting it to R134a. I finally got round to doing some deep research and after a few false starts I found Auto Climate Control in Swindon
The guy had never even seen a Sera but in about an hour he had tested it with Oxygen Free Nitrogen (OFN), vacuum tested it and charged it with RS-24. I though I was going to freeze to death on the way home - it's way colder than my Peugeot 206 which runs on R134a and recently serviced and recharged.
Cost: £116 inc VAT .................... Way chuffed!