Hi Maneesh,
I have been enjoying the lovely cold air in my '94 LS400, set at 20c with an outside temperature reading in the 30s, it is cool

.
(Sorry, couldn't resist that!)
Anyway, regarding your problem - a couple of questions:
Has the air-con always worked in the past
How often do you use it? Does it get used in the winter?
Have you had it "re-gassed" before?
The reason I ask is that an air-con system is a sealed, high pressure system. They should be air tight, and should never need re-gassing unless you have a leak.
The trouble is these days, so many people re-charge air con systems without finding the fault first (small garages etc)
If the fault with your system turns out to be that it is "low on gas", try and find a reputable AC specialist that will not just fill it with gas so that it works for a few weeks/months. A competent place will diagnose the system properly, and repair the leak before re-charging. Will save you time, money and hassle in the long run
I hope it goes ok for you,
Will