go to a very good A/C shop - one whose foreman is willing to share some reason with the A/C not cooling - NOT that "iss ko service ke zaroorat hai"
make him explain why its not cooling - if he does, he's good and for sure I'll do business with him. The regular asswipes will just try to shove chillies in your eyes.
The simple terms of my post is
start your A/C - and pop the bonnet, check your cooling fans of the radiator - they should be blowing at full speed - feel the thick (suction) line going into the compressor from the evaporator - it should be frosted or near frosted, the thinner line (liquid) should be slightly warm to touch or even no temperature difference to the atmosphere.
Get on your knees and check the condenser fins for blockage or see if they are entirely missing - in which case you are packed up for a new condenser (big kharcha)
if your lines are like what I mention and still have no cooling - your HVAC unit in the dashboard is malfunctioning - if the line temps are way out of spec - you have a thermal effeciency drop and need to have the system checked, cleaned, flushed and refilled