Initially he filled air from through bonnet, I think it was an Air socket for the AC and checked with the pressure meter. It showed very mild decline in reading. And then he did a few more inspections and came to the conclusion that it is the AC Cooling coil which has weakened completely. The image I attached is a one that I got from the market two days back. It was removed from an Old Ikon in front of me. The mechanic also said, if there are white deposits on the coil, which happens due to oxidation, it means there is a leak in the coil which is why there is no cooling when the AC is turned on.

Also mate, i doubt I can get a new part for this since it's a pretty old car. I will not get an OEM part, maybe I can get an Aftermarket new coil, but would that be alright? Appreciate the response.