Dodge Repair: Dodge Durango A/C blows warm air, dodge durango, ac service

Question
I have a 2002 Durango and this summer when I tried to turn on the A/C, it would only blow warm air. When it's been sitting in the shade, or it's a mild day, or I run it on the Highway for a while, it does get a little cool, but barely. My untrained mind immediately thought i needed to recharge my A/C so I took it to the shop. They just told me that it was a switch in the dashboard that has gone bad and needed to be replaced (approx $400 for parts + $100 for labor).
Does this sound feasible? Does such a switch exist? is there anything that I can do to double check (since I'm not in Atlanta)?

Answer
ahh no the switch that they must be talking about would be for the blower motor or the ac on off deal that sitting in the shade would not have anything to do with it working or not. Have a shop do an ac service add dye and tell u how much freon was in the system b4 they added some in.