Peter graham

hi hope someone can advise me about my 2014 a3 sportback, my air con is blowing warm air constantly, I’ve been told it’s an A-T valve on the air con unit and the cost is £478 +vat for Audi to replace said valve ! Am no longer under warranty as it ran out in may 2018 but we have mentioned it to Audi when they serviced it in February also they were told in December we thought there was a problem with it , they said on checking it they couldn’t find any problem and as it was winter we didn’t need it anyway ,but come summer the problem reared up again and now it’s been found to be faulty ! 1 is the repair bill fairly priced 2 should we have to pay even out of warranty if we’ve told them in past . Your advice would be appreciated many thanks pete