Advice on Climate Control troubleshoot

[PeterA]

Air blasted out cold today ... Will consider it solved and if it returns bring it in to the dealer.

Absent of a service call, does anyone have any advice on how to tell if the A/C needs to be serviced. Finally warm around these parts and I've felt the air coming out of the vents has been less than cold, making the car feel like its not reaching the desired temperature setting. If its as simple as adding freon, is that something I can do myself?

Thanks very much,
Peter