If your house is not getting cold enough when your A/C is turned on, It is time for a good cleaning. There are a variety of factors that may cause your A/C to not cool your house. With that said, here is a diagnostic article that provides the most probable causes of your A/C's failure to cool your house, and from there you can read it and then, step by step, rule out each possible cause listed in the article:http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Home_Improvement_Zone_Cooling_Ventilation_Systems_Central_Air_Conditioning_Does_Not_Cool.htm
Of course, a low level of Freon/refrigerant may be the problem, but there may be other problem causes as well, as noted in the article---it may just be that debris is obstructing your AC as well. Read the article, and, actually, your best bet may be to take advantage--towards the END of the above-linked article--of the text-link for Free four (4) quotes from local AC contractors in your area, and "pick the brain"--seek the advice--of these local technicians who offer you a free quote to discern what could be the problem. Also, since you may need a Freon/refrigerant recharge, you'll ultimate need this AC contractor to do it for you, since federal law prohibits the selling of Freon/refrigerant to anyone other than licensed AC contractors/technicians.