If I recall correctly "Freon"was a trade name used by Dupont for thier line of AC refrigerants. While some people may be nitpicky about using the term generically, it doesn't bother me (also certified, federal and ASE).

I am not sure it would be critical to take it to a GM dealer either, the last time I checked GM didn't yet have a set of physics that was exclusive to them. Any reputable, shop should be able to quickly and effectively diagnose the problem.

The truth is that if you are not familiar with the workings of an automotive AC system it is a good idea to take it to somebody who is. They aren't that complicated or difficult to work on (as a matter of fact the best diagnostic tools you can have for AC work on attatched to the end of a good techs arms). , but can get expensive quick.

At best you are low on refirgerant, a quick and inexpensive recharge kit may get it blowing cold again, but probably not for long. There are two reasons for this, one is that if it is low, then it is leaking, refrigerant doesn't evaporate or lose effectiveness in a sealed system no matter how old it is or how many summers it has seen. Next is it is leaking refrigerant out, it is letting air in, air has moisture in it, which will cause problems, it only takes a few drops of water to cause major damage to your system. It can freeze up and cause a line to burst, and it can mix with lubricants and refrigerants forming a corrosive compound that will destroy your components. Besides if you are leaking it is polluting for no good reason, and wasting your money, why spend $50 on refirgerant when you can pay a tech $75 to fix a leak.

It is best to get AC problems fixed quickly, a $100 job can very quickly turn into a $1200 job if allowed to go on. plus just about any issue you might have will require you to open the system, which will require a couple of steps that are expensive for a DIY guy in his garage. You will need to purge the system into an approved collection vessel, or recycler, then you will need to run a strong vaccuum on the system once you have finished the work, a decent vacuum pump capable of this task starts at close to $300, and isn't something a DIY will use often. You will also need a good set of manifold gauges, they are going to run over $100, plus hoses, another $50 or so.

Of course you can fix your AC without pulling a vacuum first, but you will not know if you still have a leak until the new refrigerant has disappeared, plus you will have a system full of moisture laden air.