Some places claim to run diagnositics for like $29.99, I don't know what that involves, but they need to run a refrigerant identifier (makes sure no contaminated refrigerants are in the system), install high and low side pressure gauges and compare readings to stock data (this can sometimes tell you if you are low on charge or if you have a restriction somewhere in your system), and finally a good leak check should be in order. Shop around town, actually I recommend one place in town, even more knowledgable than the dealer I'd like to think...Polar Bear A/C...don't know how much they cost, but they do excellent work I hear.

I'd check for you, but you'd have to wait something like two months at the very least.