2010 GMC Terrain Air conditioning not working

I bought this car two years ago and the first time I went to use the
ac it didn't work. I took it in to a gmc dealer and they said it was out of freeon they fixed because it was on
warranty. Now two years later it is not working again. I called the dealer an the think it more than being out of freeon. They want to charge 100 dollars to just look at it.
It does have auto ac and heat.
do you have an idea what the problem could be.

Thanks