As long as you use the air con all year round, the air con should perform well for a few years.
It's when the air con is not used during the winter then only used, say, during the summer that problems happen.
As well as air con gas, there is a small amount of oil put into the system to help lube the parts and keep the seals healthy. If the air con is not used regularly then these seals can become hard and so damage the sir con system.
£70 does seem alot of money. I know Kwik-Fit do it for less, I use a mobile service who for the same price, does the job on my driveway and will do a full vacuum and recharge. I think it's money well spent on a bi-annual service.Edited by: lawe