Well A/C in some mehrans works fine but 90% of mehran got heating problem with A/C and almost no cooling in trafic jams on highway it will work ok for the front two passengers.
And Sirf gas bharni hai its not always only gas the problem is if A/C system was not functional for over 4 or 5 months there can be a lot of things that might needs to be changed like compressor bearing kharab ho sakta hai expansion valve us ka ilawa ac ke bottle i mean if some body says its only gas u can tell them to get it refilled for me.
Waisa bhi ajj kal GAS is around 1500 to 2000 Rs.
Mehran jo Factory fitten CNG hogi ek if u open its petrol cup tu waha per u will see a proper support for filling valve jo ka normal bahir wala nahi lagata.
Aur pipe ke fitting sey u can know.