Hyundai Motor India — elite i20 - ac not working right from second service

Address:

Chennai, Tamil Nadu, 600125

Purchased elite i20 asta when it was launched in 2014. Right from second service i have had ac issues.ac would dip when i go for long drives. Every service they will say its fixed but once again the same issues. Off late ac dips even for local drives after i drive for 5-10 mins. If i switch off and switch on ac it would work for 5 mins. Automatic sensor also does not function.
I have been servicing the car at hyundai service center - kattupakkam and they are not able to diagnose and fix it permanently. I left it once again last week and they said its fixed, within 3 days same issues.